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post #21 of 31 Old 09-27-2007
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Bill- I was just re-reading your post where you said that at 2250R's you were making 5.3K and at 3100 you were making 6.0K. For that large an increase in your RPM's you didn't gain much speed. This would indicate to me that you were trying to push the boat past it's hull speed which would definitely be working the engine hard(heat), regardless of what manufacturers recommendations are. Most likely you are overpropped a bit IMHO.
In my earlier reply I should have mentioned that I have an Autoprop, this automatically and continuously adjusts the pitch on the blades based on engine RPM and boat speed. We get the most bang (speed) for our buck (RPM) at between 22-2500 RPM and the engine is not working too hard but is still loaded up well. We can run it all the way up to 36-3700 for short periods, or run it continuously at 30-3200 but the increase in boat speed doesn't warrant it. 15 years on the engine, couple thousand hours and it's running just like when it was new (I hope saying that doesn't jinx it :-)) John

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post #22 of 31 Old 09-27-2007
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Question Another 3GM30F Question

I, too, have a 3GM30F - a 1992 that was rebuilt in 2005. I bought the boat this summer and there was zero hours on the engine since rebuild. She starts every time and runs well but I did not realize you shouldn't run the engine at low RPMs.. most of the time I am in no rush to get off the water (as you can imagine) so I will hand the tiller to a friend, and put the rpms around 1500 while I go about getting sails down and covers on.. I kind of enjoy a nice slow putter..

However, it sounds like I should not do this? It isn't used too much - maybe an hour or two a week, tops. I know that when I get up towards the 3k RPM range I get pronounced smoking (white) out the exhaust but I have never left it that high long enough to see if it clears up when the engine warms up.. likely this is just moisture/steam, or suggestion of more troubling problems?

Thanks in advance, sorry to hijack the thread.
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post #23 of 31 Old 09-27-2007
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Bitcoal,

I think you're okay -- you've only had the boat for a short while and can't have put many hours on that rebuilt engine yet. As a matter of fact, depending on how complete the re-build was, you're probably supposed to break it in a bit at lower revs.

But in the future rather than puttering along at 1500, go ahead and push the engine harder when you're using it. Something in the 2600-3100 range is probably about right for this engine. As far as I know, ALL the mechanics/experts agree this is better for the engine in the long run. You'll also get better charging from the alternator to your batteries.

Our philosophy is that if we have to motor, we may as well do it at flank speed -- get there sooner with a better charge to the batteries. But upon arrival, we do throttle back and cool the engine down for a few minutes before killing it completely. Usually the time it takes to drop anchor or secure the mooring pennant is about right.
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post #24 of 31 Old 09-28-2007 Thread Starter
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I have the PSS shaft seal, so no bind there. I will however replace the thermistat. I think that this is a great idea, low cost and so obviosly overlooked I will keep ya'll posted. But, do to work I'll not get out to the boat for a while.
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post #25 of 31 Old 09-28-2007
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My first post here - wonderful site! Have the same engine in my parent's 1992 Freedom 38 (since dad payed for engineering school, I've been designated "chief mechanic")

Lots of good suggestions so far, especially about underloading the engine. These little beasties are made to run & run hard. I've got a small diesel tractor that I often run at max rpm - in several hundred hours of use, it has never missed a beat.

A few added comments/suggestions:

1 - Proper antifreeze level? any evidence of leaks?

2 -Can you replicate the problem? We had an experience where we overheated for no apparent reason, we suspect that we had sucked some seaweed towards the strainer & when we shut her down, it dropped away. Problem self resolved. Make sure you have an actual overheat issue & you're not chasing your tail.

3 - I heartily recommend adding an actual temperature gauge if you don't already have one. We cruise at 2,9000 to 3,1000 RPM ~6 knots. Temp is the same as if we were running at 2,000 RPM. If we push her to max throttle 3,500 rpm (woods hole against the current for example) the temp will run up 10-20 degrees.

4 - regarding the "over prop" issue - what is the max RPM you can get the engine to turn under power? As others have mentioned, should be w/i 10% of 3,600 rpm. If you can't get to rated rpm, don't immediately blame the prop, we've had an issue with a bent shaft/strut (hung up on empty mooring next to ours during storm) "robbing" power.

Hope this helps.

Last edited by hazmat17; 09-28-2007 at 09:54 AM.
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post #26 of 31 Old 09-28-2007
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Hazmat,

Great first post! Between you, Melrna, Camaraderie, and others, this is turning into a great checklist for the Yamar 3GM30F.

Your point about replicating the overheat is a good one. Sometimes it is just anomolous. But it's probably good to run through the checklist anyway.
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post #27 of 31 Old 11-24-2007
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I have the 3gm30 and am getting black sooty smoke after 2400 rpm. new exaust elbow, filters, replaced injectors. adjusted the valves and still the same.
Compression test #1-500psi #2-400 and #3 is 410. was told that a new 3gm30 wont get over 460psi so either its something else or the gague is wrong. So if the gague is off it's about 8% off so that brings down my loest psi to the 360 ish range and I see a problem..

Question? Time for a rebuild? if so who? or can this be done with a book and a rebuild kit, or should I upbrade to the yanmar replacement what ever that is. Many thanks for the help
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post #28 of 31 Old 11-24-2007
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To address the overheating issue of the original poster, is it possible the water pump drive belt is slipping?

It would make sense that as the rpm's built up there would be more strain on the belt as the impeller moved more water. If the belt tension was a little light, it could slip while turning at higher rpm's and grip again with less strain.

I run my 3GM30F at 2800-3000 rpms. It starts to smoke a little after that and I'm nearing hull speed anyway.
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post #29 of 31 Old 11-28-2007
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With all the symptoms you have posted over the last month, you may very well be at that rebuild vs. new question. Unless you are an experienced diesel mechanic, I wouldn't recommend trying to rebuild it youself. When I had mine rebuilt this summer, the parts were about three times the labor cost, and did not include a new crank crank ($900) or connecting rods.

For the record a re-manufactured engine from Mack boring is about $5200 + freight & installation; I believe a new engine is north of $10,000. Any Yamnar dealer can give you a quote on both options.

If you want more detail contact me thru the IP homeport site

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post #30 of 31 Old 11-28-2007
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With the huge hassle of having to re-build the motor (I did it once, top end, on the Volvo MD17C), I would throttle it back to a constant rev where it did not overheat and leave it at that.
If you have reasonable starting, and mid-range power, I would not touch it. Throttle the older motor back until it is at ease with it, and stay there.
Although 86 % of full load sounds OK for a newer motor, I would not rev the old Volvo to more than 2000 rpm for any length of time. It will take flat out for a wee while, but I don't push it, and that is with the top end rebored and valves re-cut, and collant jackets de-scaled.
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