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Discussion Starter · #1 ·
Greetings - This is my first post, though I read this forum quite a bit. I know this issue has been addressed elsewhere here, but I haven't quite found what I seek, I guess.

I have a 1980 Sabre 28 w/which I bump around MidCoast Maine. It has a raw water cooled Volvo Md 7/A . I bought it 4 years ago and it has been relatively hassle-free. I love it. Anyway, the waterflow out the exhaust isn't what it should be. Additionally, the Temp Gauge will jump up if I run it full throttle too long, but quickly settles to normal when I ease it back. From a usage standpoint, this really hasn't been much of a problem, I just don't run full, or close to full throttle often and I've managed. My buddy is a marine Engineer and he says it could run that way for the next 10 years w/out issue provided I keep an eye on it.

Anyway - I Winter and Service the boat at a nearby Shipyard that I like thus far. They have told me that these engines essentially rot (rust) from the inside out and outright engine failure is inevitable, but measures can be taken to prolong it's life. I guess I agree, I'm not mechanical but am sloooowly learning a bit via this engine. Below is an email from the yard, I'd be most appreciative if some of the mechanically inclined folks here could share your thoughts. Thanks much - Chris (I've changed the names to protect the innocent)


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On the engine, I met with Joe, our diesel mechanic on the engine. Last year we did the following to help with the cooling situation.
1. We removed the elbow and cleaned it. It was in pretty good shape.

2. We removed the thermostat and its housing. The housing was filled with rust and sediment which we cleaned.

3. We replaced the thermostat.

Joe and I discussed trying a radiator cleaner (ex: Rydlyme) on the engine. He recommends against it. Loose sediment dislodged by the harsh cleaner may cause clogging down the line.
He recommends a thorough flushing it with fresh water and then running non-tox antifreeze through it. This is leaves the engine clean and protected for the winter. Remember that this is an old saltwater cooled engine. It’s life-expectancy is limited. There is nothing we can do to reverse that, but the right measures might slow down its internal deterioration.
On the exhaust manifold, if we can free up the bolds to remove it, it might benefit from an acid bath. BUT, as with any rusted bolt, you run the risk of snapping it off. If one were to break in the wrong place, we might have to remove the engine to repair it. I’ll have Joe look at it and see what he thinks.
Guess that’s it. Mike
 

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Discussion Starter · #3 ·
Hmmm, Good question. I guess I'm having a hard time remembering at the moment. I think it generally holds pretty steady, whatever the temp may be at the moment, and moves closer to the red w/increased throttle. Running time doesn't seem to impact it, it will stay at decent temps for long periods of time provided I don't over-throttle.
 

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If the thermostat is working, the wee needle will rock back and forth. It climbs slowly, then the thermostat opens and it drops quickly. As long as it does not STAY in the red it is not a problem.

If it is not wobbling, then the thermostat is not closing. It must be opening, otherwise the motor would fry.

Take it out and put it in an old pan with water and take it slowly up to boiling point. You should see it opening. In an emergency, cut the centre mechanism out of the thermostat and just leave the big hole down the middle. You have to put what's left back in there again as the outer rim is rubberised and it forms the seal. You will cool then, unless the fluid ENTRY ports are blocked or restricted. That problem is easy to fix when you take the exhaust manifold off.
 

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I see nothing wrong with their email.

They just replaced the t stat right? So why not run the engine to see if it is now working OK. that is the easy thing to do.

I have one of these engines (and a spare!). I had a similar problem, engine would run fine then spike temperature. Took a long time to sort out. I short I was getting an intermittent air leak on the suction side of the water pump.

Water comes from the strainer, through the transmission, to the water pump. The fitting on the engine side of the water pump was causing my problems, an improper fitting. They used silicone instead of a copper compression washer.

Also the fittings to the water pump, and exhaust Mansfield, and thermostat are a weird slip in type.

I have taken off the exhaust manifold on both engines with no problems. I have talked to others who have done the same, all without issue. If you do take the exhaust off tend to the fuel return line banjo fitting while there. Replace or modify so that you can replace the hose without removing the manifold again.

These raw water cooled engines run around 130°F, but mine seems to be running cool nowadays. Go figure.

Good luck.
 

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I agree with your quite astute friend .. with the exception of using so-called non-toxic anti-freeze.
The issue is that so-called 'non-toxic' antifreeze usually has NO anti-rust compounds. Without anti-rust compounds, especially during winter layup, the protective 'black rust' that forms in a cast iron engine block and exhaust manifold will slowly turn back to destructive 'red rust'. These castings are all 'stratified' (like an onion) ... a phenomenon when the castings cool when theyre made. What will happen is that the red rust will penetrate these thin stratification layers and produce 'very destructive' red rust 'platelets' (slab-rust) .. which can easily migrate and block or partly block the cooling system, .... especially in the exhaust manifold. This slab rust if it progresses will penetrate the internal walls of an exhaust manifold eventually causing pin hole leaks between the 'gas side' and the 'water side' ... and then water will wind up inside the combustion chamber.

Descaling of an engine is quite important, especially in a raw water cooled engine; AND, especially in a raw water cooled engine whose thermostat allows full water flow at engine temperatures at greater than 155°F. When sea water (and to a lesser degree - even fresh raw water cooled) is heated much above 155° the carbonates that are dissolve in the water will 'drop out' and rapidly form 'boiler scale' on the internals of the cooling circuit (and in the injection elbow).
With a raw water cooled engine, Id recommend 'descaling' with a commercial boiler descaler such as RydLyme (RYDLYME Marine: The Ultimate Biodegradable Marine Descaler! | RydLyme Marine) followed by running the engine at nearly 'full speed under load' for several HOURS to reform the important and protective 'black rust' (ferrous oxide). This recommendation includes periodic 'descaling' of the 'raw water side' of engines with 'heat exchangers'.

First step in this process before 'descaling' is to verify the volumetric flow of the cooling water .... look at your engine specs. Look for water flow output at a listed rpm --- will be approx. "2-3 gallons per minute at a 'x' rpm". Take a bucket and stop watch to the exhaust outlet, run the engine at that spec. rpm, and verify the RATE in gallons per minute of cooling water output.
If not up to spec. .... find the problem and fix it. (this includes removal of slab-rust from inside the exhaust manifold (followed by pressure hold test to verify NO pinholes). Once cleaned and descaled reevaluate the output volumetric flow and record for future reference.

DO NOT use muriatic or hydrochloric acid, etc. to descale a cast iron engine ... use ONLY 'inhibited' boiler descaling compounds. Why dissolve 'good metal' inside the engine??????
DO NOT ever ever, drain and leave 'dry' a cast iron engine for long term storage .... causes massive internal 'slab-rust' formation .... always use an antifreeze WITH rust inhibitors!!!!!!!!!! when laying-up a marine engine.

Again - LAST procedure after descaling or before haulout/layup: RUN HELL out of the engine to 'heat soak' it at operating temperature for several HOURS .... to reform the needed and protective 'black rust' in all those internal water passages.
With a raw water cooled engine its probably best to temporarily switch the usual 150 degree thermostat for a 180° thermostat for the 'RUN HELL' out it to better heat-soak the engine procedure to reform the internal 'protective' black rust.

Marine engines hardly ever 'wear out'; the usual 'end of service' life is 99% of the time .... internal ROT and Corrosion. Keep the internal protective BLACK RUST intact and you'll have a long lasting marine engine.

hope this helps. ;-)
 

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Discussion Starter · #7 ·
Wow. Thank you guys. I appreciate the thoughtful responses and the time taken for each. I will absorb as best I can and apply. I should have been clearer: that email was last Season's (2013), and the waterflow/temp problem I described persisted this past Season (2014). If you have additional thoughts I'm all ears! Thanks again! Chris
 

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Well I hope 30 is OK as I have one of the same vintage.

Mine runs cool, about 130F. I'm told that is normal as it is salt water cooled and they use a lower temp thermostat.

I can piss more water than this thing puts out, and I've an aging prostrate.

I had my exhaust manifold off and was able to clean it up pretty well just using mechanical means. If you do take it off look at the fuel hose connection to your fuel pump, you may want to change it so that you can take the hose off without removing the exhaust manifold, I could not.

Come to think of it, I've heard a lot of advice that these things rot from the inside out. May well be true. I don't know I've actually ever heard someone say "Mine rusted out."

Other than exhaust elbows, but that isn't unique to this engine.
 
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