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Confused about which oil weight to use

15K views 37 replies 9 participants last post by  Rusty123 
#1 ·
The shop manual for my Yanmar 2QM15 specifies either 10 or 20 straight weight oil, depending upon outside temps. I realize that when the manual was written, modern multi-weight oil didn't exist, but my understanding is that because the engine was designed to operate with 10 or 20 weight oil when at operating temperatures, I should use a multi-weight oil with a similar operating temperature weight (something like 5W20, for example).

Problem is that the readily available diesel oil doesn't seem to be available in this low viscosity. For example, Rotella T, which many recommend, comes in 15W40 and 10W30, both of which would seem to be too thick.

To add to my confusion, since this is a raw water cooled engine, it operates much cooler than a fresh water cooled engine, making the use of too thick of an oil even more of a problem.

What am I missing in this equation?
 
#5 · (Edited)
The main difference is in the cold start... which in most pleasure craft will not be all that cold.

I've used Rotella T 15w40 in EVERY engine I've owned for the past 35 years. I get 250,000 miles out of every vehicle. But 97% of my miles are low rpm, seldom over 3000 and never over 3500. Even on the lawn mower I do not run wide open... 80% is my max. Once warmed up its in the 15 to 20 wt zone. 40 is at cold temps at whatever the standard temp is. They are all almost grease at below 0, but I highly doubt you'll be sailing at 20 below. Start and let it warm up before working as is proper for any engine and I expect you'd be fine. This doesn't work for some of the modern high rpm automotive engines though. They are a different animal.

Most of the marine sail applications on general use are likely low rpm high load... exactly what the Rotella 15w40 was designed for. It will keep a Mack 350 semi engine going at 100% for a million miles before a rebuild. Been there did that.

Now there is another potential issue though... that of detergent vs non-detergent oils. On many old engines pre 1950 or so that ran non-detergent is the shellac and gum that is actually doing the ring sealing. Switching to a detergent oil and they can start burning alot more oil. Its doubtful your in this category though.
 
#6 ·
I recently switched to Shell Rotella 15W-40 in my Yanmar 2GM and it is now easier to start when cold. The recommended straight 30-weight oil seemed too thick for winter and loaded up the starter more (as you would expect). This engine is also raw-water cooled and never gets very hot. To flush out the old 30-weight completely I did an oil change after about three hours on the Rotella and now do it twice a year, regardless of hours run (my engine does big hours by pleasure boat standards).
It is said that any damage to an engine happens in the few seconds after starting, before the oil gets to all the bearings etc, so lightweight has to be a good thing. Even though the manufacturers always want you to use their own expensive 'home' brand oil, I have run a fairly cheap locally-produced 15W-60 semi-synthetic diesel-engine oil in air-cooled dry-clutch motorcycles for many years with no issues.

With oil, you will get dozens of different opinions, sometimes clouded by a commercial interest. Mine is that any oil these days has to be reasonably good to make it to market and I would place more importance on twice-yearly oil changes than any particular brand. Shell Rotella is as good as any, but if I couldn't get it I would buy whatever grade and brand suited the engine. My other belief is that there is nothing wrong with mineral oil in a marine application, and in fact, full synthetic is probably a waste of money (ducks for cover.....).

If it is recommended to use straight 30 in your gearbox, stay with that. Unless it uses something else, like hydraulic fluid, of course!
 
#8 ·
I have used the 15W40 MotorCraft from WalMart. I hope you all don't blow a gasket at the oil I use. My motor hasn't yet. But, the specs read that it exceeds standardized oil
at that SAE. Does anyone have any experience with these matters that should advise me otherwise? I have a Island Packet 32. A 3GMD yanmar (20 HP) was put in, in place of
the previous, fresh water, coolant (24 HP). Does anyone know if this is too small of an engine for a 22,000 IP that is 32 feet long? thanks. New to Sailing.
 
#9 · (Edited)
As long as the Motorcraft has the right rating, it's a Ford product and probably ok. You might want to shy away from the generic Walmart brand although they are probably all ok in reality. I'd be a bit leery about an off brand's QC and would worry that what it says on the can might not be what is actually inside. Could be a REAL expensive error to save a couple of bucks. I use Pennzoil in my cars and trucks. My last Subaru was still running fine at 365,000 miles when I traded it. Changing oil religiously in cars or boats, diesels or gassers is the key to long engine life. With Yanmar, it's 100 hours which comes around pretty fast. I never go cruising without at least 3 oil changes and filters on board.

The old CD rating is listed for Yanmar diesels. It's not really available anymore but the HEAVY DUTY DIESEL C ratings are what you need to look for.http://www.api.org/certifications/engineoil/categories/upload/motor_oil_guide_2010_120210.pdf Light automotive diesel oil won't cut it.

That's a perfect engine for your boat.
 
#10 ·
Thanks Smurphny,
Last week, I ran the motor in idle, in neutral for about 25 minutes, it had plenty of water flow in exhaust, Then, I thought it might be getting too hot,
So I reved it to 2500 for 15 seconds, then lowered RPM to idle in 5 seconds,
and shut it down. For some reason, the motor was very HOT, and it froze for about 2 hours. Since, I did not know it froze, I tried to start it after about 20 minutes after I shut it down, and It blew the starter aluminum cast shroud over the gear teeth into two pieces. Luckily, since this happened once before,
I had bought two, to have a spare, and replaced it. No aluminum cast pieces went into the flywheel cavities. But, does anyone know why it got so hot,
while running in idle?
 
#13 · (Edited)
Overheating to the point of seizing up is really bad. It's likely the cylinder walls have been scored already. You can't do this too many times until the engine is toast. If it will turn over again: 1. Change the oil and put in some Rotella straight 30 weight. Look at the old oil to see if it's milky which will mean water is getting into the oil somehow. This could cause the overheating. 2. Drain the anti freeze. (I would take the end cap off the heat exchanger to see if something is clogging it) If it's a standard raw water cooled engine ignore this. 3. Replace the thermostat or just take it out until you are sure you're getting coolant circulation. 4. Refill and start again but don't let it get that hot again.

Personally, I'd probably be pulling the head off after two seizings to check for cylinder damage before taking a chance running it again. This would also let you look at the water jackets to see if they are full of silt or something. The fact that water is running through the exhaust manifold doesn't necessarily mean enough water is running through the block.
 
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#11 ·
Posted a similar thread on "Bob is the Oil Guy". Amazing how varied the responses have been.

One correction to my original post: Here is what the manual actually calls for:

<50F: 10 or 20 weight
50F - 60F: 20 weight
60F - 95F: 30 or 40 weight
>95F: 50 weight

Based on my research, and forum responses that seem well reasoned, I need an oil with an hot viscosity of 40 or 50, and a cold viscosity as low as possible (for ease of starting and initial start flow). Something like 15w40 in conventional, or 5w40 in synthetic. Pretty much confirms what most people recommend.
 
#17 · (Edited)
Back to the original topic.... I've been using Shell Rotella 15w40 for 35 years in all my diesel and most of my gas engines (old school low rev type). Only in the very coldest part of winter do I use a 10w30 but then the temps are low enough that its rather hard to sail in unless its an ice boat.

Its my understanding from a local ag and desiel repair outfit that in recent years there have been changes to Rotella T and it may not be as good as it used to be... Something about the Chinese (imagine that!) now manufacturing, but I haven't been able to verify that as yet. He will not use it anymore and is a Dodge Cummin fanatic, but works on any diesel. Like me he swore by it for years. I haven't changed out from it yet and trust me I will if needed.

Good luck on your cooling issue.

Dave
 
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#12 ·
DixeyJulie, to have an engine seize through overheating once is bad, twice is terrible!

You say you have water flow through the exhaust, so the raw water side seems OK. However, what is the thermostat like? You could remove it and try running without it. However, if your engine has a sealed (freshwater) system which is being cooled via a heat exchanger, there could be a problem in that side of the system. Low coolant level, an air lock, circulating pump shot. An air lock? Sometimes happens after the coolant has been changed.

I doubt the wrong grade of oil could cause overheating like you describe. If there was a lack of oil pressure due to a blockage, failed lube pump, low oil level or foaming you should get an alarm or red light warning in time to shut down.

When you do shut down make sure you let it idle for a few minutes first. Although Yanmar recommend running the engine up to high RPM if it has not been working very hard, they still expect that after having done that, the operator will bring it back to idle for a few minutes to stabilise temperatures.
 
#14 · (Edited)
(edit: I replied from the original post on your over heat on page 1, didn't see the previous replies until just now. I repeated a couple things, but also added a couple. No matter what you need to get to the bottom of this before using this engine again... if its still usable.)

Ouch!

Cooling circulatory issue. Raw water cooled? or Freshwater cooled?

If raw water cooled, I'm not sure, but I believe there is a thermostat that provides coolant flow to the cylinder water jacket... it bypasses what it doesn't need to the exhaust (so you'd still see flow even though its not being circulated through the engine). I'd bet that thermostat stuck closed, or failed to open enough for whatever reason. Line blockage post the thermostat is also a candidate as severe corrosion in the water jacket itself that can break free and plug the flow downstream so it prevents circulation.

If freshwater cooled... the raw water outflow from the heat exchanger does the exhuast cooling so it would still show in the exhuast. In this case, circulation was prevented in the freshwater side of the system (water pump, inoperative thermostat, pinched of or blocked line (blocked is unlikely though in the freshwater side of the system, but a pinched line due to fatigue is still possible). Its also possible in this case the the heat exchanger is tired... but unlikely.

Does your system include a temp gauge? Worth their weight in gold! Also some systems have a high temp shut down built it... if yours does...it must have failed too.

Obviously I am not looking at your engine... but from your description, its what it sounds like a thermostat failure or blockage to me or at least a good possibility of it.

Even though you replaced the starter... seizing likely scored the cylinder walls... while it may still run... it will start taking oil and have a reduction in power. Time for a rebuild or at least a refresh honing and new rings on the piston.

Good luck, Dave
 
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#15 ·
Thanks again, it sounds like I need to check the water thermostat.
The starter had broken once before (About 6 months ago) due to, trying to get the motor started with ether. I had been having some problems with starting and a mechanic got it started with ether once. Well, somehow, it was too much, and cracked the starting casing. on that starting effort. (Now, don't laugh too loudly at my ignorance). I am just learning diesels, for the first time.
So, that was the reason the starting cracked. The motor has run fine, (for some reason I cannot explain, and started on first turn of the key ever since; except for the recent episode of getting hot, at idle. (The motor did, once, have the warning heat alarm sound off a month ago), when my wife got confused on which way the thru haul raw water intake valved turned. She turned it off, and thought she had turned it on). So now, I have drawn a picture beside the thru haul valve for the raw water for ON and OFF positions. But, on this occasion, the warning heat sensor alarm did not sound off. I am wondering if a plastic bag might have been sucked to the the outside of the raw water intake. But, now, it could be the thermostat needs checked. I have since, ran the motor for over 20 hours, with over 15 different starts, up and down the ICW in Florida, travelled over 70 miles, and have not had the least bit of motor problem. But, I was glad to have ordered the extra starter (since I switched it out, in 20 minutes and was going again), without needing to call for a tow.
Is it much work to pull the head? I have never done it. And I guess the pattern of re-tightening the headbolts and the torque is in the manual? Right? And, what does scarring look like on the cylinders? Are there any pics on youtube that show a scarred cylinder. Wouldn't I have to pull off the block in order to replace the rings? Does a compression test simply tell me if the rings are shot? It still starts easily now on the first turn of the key.
Is that a good indicator of good compression? The rating of the 3GMD is 20 HP at 3400. The RPM goes to 3600, when running at full throttle. And I move at 7.3 knots. Haul speed is 7. Thanks so much!
 
#16 ·
If it's running ok now maybe you dodged a bullet. Keep a close watch on oil consumption. Diesels will always need a top-off every 20 hours or so but any more than that and you should suspect some significant cylinder scoring. The next time you're not out cruising, maybe pull the head and check it out. Scoring looks like thin lines in the walls. The engine will still run with some scoring but you should see a lot of smoke if it's in need of immediate repair. As mentioned by dem above, you might want to re-ring and hone the cylinder walls. A danger is that the pistons and rings may have been damaged which can result in catastrophic failure and trashing the engine entirely. Also, the bearings may have overheated and become out of round slightly but this is probably not true unless you really baked it.

Gasket sets and rings for these are not terribly expensive. I recently re-ringed my 3GM30F for around $400, including a complete gasket set with a lot of extra gaskets that may be useful in the future. Before I bought this boat, the new engine had sat for 6 years. The rings never seated correctly. I was able to pull the pan right in the boat. If you can get the pan off with engine in place, it's not a difficult job. You can mount a mirror in the bilge so you can see what you're doing. Mark all the rod caps (they are probably numbered already), make sure you put them back in the same direction they came out so the oil weep holes are in the right direction. When in doubt, label it. Taking pictures before you take stuff apart with a dig. camera is also often helpful. The objective is to have no leftover parts.:) A ball-end hone is recommended but I like an old style stone hone. Both are fairly cheap. You will also need a ridge reamer if there are a lot of hours on the engine.

If you need a ridge reamer then you ought to check as to whether you need oversized rings. Also check all the journals to see if you need new bearings. I would only leave the old bearings if the engine has very few hours on it and the old plastigage as ok.

To do this kind of work you really need the shop manual for this engine as well. All that said, if you have never done this kind of work and don't feel confident about doing it, it would probably be better to yank the engine and bring it to a shop.
 
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#19 ·
Without a thermostat sometimes (depending flow characteristics) the flow can be too much and prevent full operating temp...

I supposed it could be possible that the stay time around the cylinder could be too short... too short to absorb enough heat.... but I really don't know... I think it might rare though or maybe impossible for a design to be that way and actually get real hot.

Is yours raw water cooled or freshwater cooler (i.e using a heat exchanger)? It would help in determining the culpret if we knew. (forgive me if you already stated that somewhere, but I haven't seen it if you did)
 
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#20 · (Edited)
That makes one wonder why someone took the thermostat out. Possible overheating before? Taking the thermostat out causes the engine to run too cool, making it run less efficiently. I've heard that the valves can be affected because of too big a temp differential between too cool a casting and the hot valves. I would suspect some sort of clogging of the water jackets either by rust or silt that has accumulated. https://www.google.com/search?q=rust+clogged+cylinder+block&client=firefox-beta&hs=Ls7&rls=org.mozilla:en-US:eek:fficial&source=lnms&tbm=isch&sa=X&ei=7Jj9UbmoG7S24APv2IDgDw&ved=0CAkQ_AUoAQ&biw=1280&bih=564#facrc=_&imgdii=_&imgrc=LGC9_46s4ID-sM%3A%3BGiLHAdOvMgo9hM%3Bhttp%253A%252F%252Fwww.seatonsmarine.com%252F0_0_0_0_383_254_csupload_1365365.jpg%253Fu%253D616639612%3Bhttp%253A%252F%252Fwww.seatonsmarine.com%252FWinterize.html%3B383%3B254Maybe if you can remove block drains or the engine zinc or find a freeze out plug, you can fish around with a coat hanger or fish tape to see if the water jackets are clogged. It's possible that clogging is causing hot spots so that even though water is flowing out the exhaust, it is not circulating around the cylinders.
 
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#21 ·
What about the ratings? SE, CE, CD, BS,/. MIL SPEC etc. I can hardly find an oil that has the correct spec any more for the Perkins 4108. I think the modern Oil is fine, just wondered about these?
 
#23 ·
I will removed the anode above the transmission and water flowed out freely there, I did not find any impediments inside, but, I did not do any scratching inside with a clotheshanger, I will do that and see what I can find out. I will also locate the freeze plugs and check those areas. Where is the second anode location? I do not see another one in the 3GMD diagrams. Also, the 3GMD runs on the raw water from the thruhaul valve. No radiator.
Thanks!
 
#24 · (Edited)
In the manual for my 3GM30, I believe there is a water flow graphic. Maybe you can look at the one for your engine, look at the path of the water to see where there may be some clogging. The head gasket area would be my guess. Is it possible that someone put a head gasket on upside down or reversed in the past and blocked some ports? If you could isolate the head and put a LITTLE flow through it with a hose, maybe it would tell you if it was blocked. Be careful putting pressure with a hose as it can ruin the head gasket seal and get water in the cylinders. It's usually not recommended to do that but if you're going to pull the head off anyway, maybe you can try it. How many hours are on this motor? How long has it had salt water running through it? Cast iron becomes crystallized by salt water after many years and at some point actually becomes porous, especially if the engine is not flushed between uses with fresh water. Your engine is probably not old enough for that but it's something to consider. http://www.oldmarineengine.com/technical/corrosion_1.html

By the way, your 3600 RPM is quite high if you're running at that RPM continually. Most of these reach hull speed at around 2800 so revving up any higher is pushing the limit.
 
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#25 · (Edited)
I second the high rev comment. 3600 is pushing it. Actually on most long stroke engines its starting into the "screaming" definition. You may be a little underpropped too, but just pull the throttle back off 100% to the 85 or 90% level... you engine will love you for it. 100% of capacity work on any design is hard on em.

Its not quite screaming on many of the more modern designs with square or under-square designs in light duty applications... which could be why it may not have triggered a mental alarm to you. But its definitely pushing the upper end limits on long stroke old school designs.
 
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#26 ·
Thanks to both of you for your comments. I have read that I should run at the top RPM to blow out carbon, once in a while for about 15 minutes. So that is when I hit the 7.3 knots at 3600. I do usually run at 2900 and am doing about 6 knots then. I do not notice any smoke of any color coming out at that speed. So, I am wondering if I should get a mechanic to tear it down to inspect the cylinders, and hone them, and to replace the rings, -since it seems to run fine most of the time. I want to take a trip to the Bahamas, and I certainly do not want to go there with the idea that I might have a motor that is ready to die on me. How many hours labor does it take normally to tear it down, hone it, replace the rings, and re-assemble...do you know? THanks!
 
#27 ·
Since the engine is not blowing a lot of smoke, your problem is the unexplained overheating. I would investigate all the possible causes before spending many thousands to have the engine removed and rebuilt. The old saying, "If it ain't broke, don't fix it," may apply here. These engines are tough little buggers. Are you absolutely sure it's not just a bad impeller, a blocked sea strainer? Is the pump the right pump? Is the bronze in good condition or maybe worn beyond limits? The water you're seeing coming out of the exhaust may not be adequate. Is there an air leak into the system? Check all the hoses and clamps. Is there an anti-siphon loop letting in air? Look for not-so-obvious small things before jumping. If you can't find the problem and you are not comfortable removing the head yourself, maybe paying a good mechanic for a few hours to further investigate the overheating would be a good first step before spending a lot of money. That missing thermostat is a big clue. It's likely that this is not a new problem.
 
#28 · (Edited)
Good day DixieJulie

Once you eliminate the simple things as mentioned above there is something to think about...

Since it is raw water cooled and salt water.... its a bad combination for any cast iron or cast steel (doubtful) engine cooling system. Even with freshwater flushes it still builds, just slower.

Not trying to alarm you and I do not know how old or how many hours are on you engine... but if its older there is a good chance of rust scale buildup inside the head's cooling passages as well as the cylinder walls cooling jacket. This restricts the flow gradually over time and they start running warmer... when it gets past the point that the thermostat can compensate by flow increases they will start to over heat. The fact someone removed the thermostat to try and increase flow may be an indicator it maybe reached and exceeded this point. In extreme conditions actually eat through the cast iron in the head into the combustion chamber or the outside. I have an old VP MD7A... that was raw water salt water cooled out of FL... When I dissembled it, you wouldn't believe what those cooling passages looked like... 30% flow at best.

But you said it was an intermittent overheat? Could be you haven't quite reach the junk point, but it could be an indicator of scale breaking loose and causing a downstream temporary blockage. If it were I experiencing this shortly before a long sail... I believe I'd be pulling the head and seriously inspecting all the cooling system, but I am mechanical and have been inside a lot of engines in my time. Usually a head pull is not all that hard or costly and you can determine many things on its condition (including the valves and cylinders).

If you do or have it done... any linage you open... replace with new... on principle. Some shops will do that by default... some not. Make sure they do. Cheap insurance.

If its only the head... a replacement head will solve part of the problem. The cylinder jacket is a bit harder and would require a total dis-assembly and cook out... and then pressure tested. That gets into major money as its a total rebuild. The problem long term is raw water cooling.

The boat I just purchased last fall is raw water cooled. Since I am swapping engines anyway I will convert to freshwater cooling and a heat exchanger just on principle. If you plan to do all salt water sails I would seriously consider this... especially if you rebuild or replace your current engine.

Before leaving on a long sail away from normal service availability... its good this happened in a way, as you can address it now.

Dave
 
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#29 ·
Drifting off subject a little, but to revive the old debate about whether to convert a raw water engine to fresh cooling is worth the money.
Personally, I don't believe it is. Raw water cooling is simple and cheap. The key to long engine life is frequent use and flushing with fresh water prior to any lay-up. If you are not using the engine frequently, a fresh water flush every time you shut down would be a good thing to consider. Because they don't run as hot as fresh water cooled engines, they may wear a little faster, but hey, just how many hours are we talking about over, say, a 15 year life?

Fresh water cooled engines still have salt water coming in to the heat exchanger and being discharged via the exhaust, so corrosion will occur in those components anyway. Heat exchangers usually have zincs to replace, just like those in the block of the salty engines. Heat exchanger tubes get salt-encrusted and weed in them, just like their salty mates. The difference in engine life might be 15 years for the salt (which I achieved with a Yanmar 2GM and it was still going strong when I sold it) and 20 years for fresh. Plus more hoses and another pump to deal with, and possible heat exchanger replacement at the 10-15 year mark anyway, so would the additional cost of purchase and maintenance be fully recovered in that time span? About break evens whichever choice you make, I guess.

Sure, if buying a new engine, I would consider fresh water cooling if I thought that I would be keeping the boat for more than 15 years. My current 2GM is now 6 years old and there is at least another year in the original exhaust elbow - thanks to continuous summer use and end of season fresh water flushing.
 
#30 · (Edited)
Good day avicola...

Part of that discussion would obviously be how old the boat/engine when one got it. Since I am a poor man... any boat or engine I get is about 20 or 30 years old. If one buys new and trade off every few years then its a moot point. I am not in the category, although the concept of disposable everything just always seemed so wasteful to me.

On the two engines prior to this latest one they were raw cooled in salt water... pretty much killed the engine's cast where as all the main mechanicals were totally rebuildable, refreshable, or simply just fine. I guess killing a block or a head casting simply because one can afford it just goes against my grain I guess. Cost effectiveness is minor up to a point. See, I'm from the school that proper and complete maintenance and non abuse will let an engine more or less be able to keep running almost indefinitely. It's likely I'll get 400k on my 3/4 ton V8 and better than a million on my cummins... before their first rebuild. marine is no different... take care of them and they will take care of you. Yea, manufactures and their service departments hate people like me.

The 1975 S30 Farymann antique I recently purchased is raw water cooled but was in the fresh water of the great lakes most of the last 20 years... cooling passages are in good condition... compared to 30 year old ones that came out of FL or the Chesapeake, its a diamond.

As one who restored and showed true antique engines for quite a few years... and take what many would see as just a hunk of rust and have it running inside a week or two (depending on if it was complete and you have to know what to look for), engines from the 70s and 80s are very modern in comparison to the teens and 20s. It just seems disrespectful to any engine that way by letting them just rot from the inside so to speak by killing the casting with salt water. Someday they will be 90 or 100 years old too. My oldest show engine is a runnable 1907, yes a 105 year old Callie Perfection 2 cyl inboard marine. I get a special smile bringing a 80 or 90 year old engine back to life, running for the first time after maybe 60 or 70 years of neglect.

I haven't priced heat exchangers and an extra pump yet.... maybe I won't convert if its too expensive. But then I am not sailing (yet) in saltwater only the Great Lakes. It will be converted before I do saltwater however, on my principles. The heat exchanger is disposable, the engine is not in my mind. You all are welcome to do as you like... its a semi-free country. Its just my opinion.

Dave
 
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