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Over Heating

bad_habit

New member
"I have a 1987 5.7 Mercruiser

"I have a 1987 5.7 Mercruiser with 3300 hours. each year for the last 3 years it has started the season with an overheating problem at low rpms. I change the impeller and it runs fine.previous to this I usually changed the impeller every 3 years as a precaution. Has anyone ever done an acid flush in their motor and do you think this might help. The boat is used in fresh but I thought I might have some excess buildup of silt and rust.
Thanks, Rick"
 
I was told that the impeller s

I was told that the impeller should be changed every season.But depends on who you talk to.
 
"Richard
If she is fresh wate


"Richard
If she is fresh water cooled (closed cooling System) you may have a build up of crap inside your heat exchanger, that would be a good place to start.
Are you also sure you are getting a good seal on the water tube that runs from the top of the pump to the top box in your leg ? I have seen these loose enough water at low RPM to give heating problems. when the top seal is damaged.
As for changing impellers every season, opinions are divided, its been 3 seasons now with me but my boat is on a moring for 8 months of the year and then I regularly run and flush the engines when it is out of the water, my theory is the more you can keep the impellers moist the better.
Your climate or conditins may not allow you to do that though.
Regards
Peter"
 
"Thats a LOT of hours! Impress

"Thats a LOT of hours! Impressive! @ 12 gallons an hour and a weighted average of $2/gallon, you've spent ~$72,000 in gas. Mr Messner is a serious boater!"
 
"Richard:

Are you saying th


"Richard:

Are you saying that your engine is RAW water cooled (no heat exchg) and never been in salt water? If this is the case I would expect there is an accumulation of rust, scale and silt in the block, heads, manifolds and circulating pump.

Before pumping acid into the engine, with the engine cold and off, REMOVE the water inlet hose from the outdrive behind the engine to prevent back flushing debris into the outdrive. Then try flushing the exhaust mans. by removing the drain cocks, disconnecting the water hoses at the T'stat and inserting a garden hose nozzle into each one. Keep probing the drain cocks to keep the crud coming out with a good flow.

It is a little work but you can remove the block drain cocks and the front circulating pump and flush the block thru the front water holes. With the pump off, remove the T'stat housing and flush thru the intake manifold.

I had to also take the T'stat housing apart on my 87 4.3L to remove the scale and rust using a Dremel with coarse sanding drum. Passages were heavily scaled with rust to the point the T'stat was frozen in place. You could just remove the check valve ball assy T and soak it in muriatic acid to disolve the crud. You may need to dilute the acid by 33-50% with water. The same acid wash can be done to the exhaust mans. and risers.

Just DON'T put the acid into the block since it may affect the head and other gaskets. It may be OK to put a radiator flush into the block via the T'stat housing w/o removing the circulating pump and let it soak 5-10 minutes and then flush it out.

Guy"
 
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