Universal Diesel M25X overheating

[glassdad]

We went out on Saturday for an easy afternoon sail. I started the engine and let it warm up at idle. I backed out of the slip into the channel and the engine temp started rising. At idle it will run warm. I increased RPMs to pick up speed and cool the engine. Instead of dropping, down the temp continued to rise. The exhaust was still spitting water out although I thought it was a little light. I but the engine in idle for a moment, then reved it up again. The temp continued to rise up to the 180 range. as I turned around and went back to the slip, the exhaust stopped spitting water.

I got in to the slip and let the engine cool for a short while. The cooling water was full. I figured it was the salt water impeller. I opened the pump and water flowed in without any restriction. The impeller was in good shape, no nicks or tears. I cranked the engine and the impeller turned.

I checked the oil and it read low. The next day I went down to change the oil and checked the level first. It read full but it was dirty. I changed the oil and filter and started the engine. It runs fine. The water spits out the exhaust and the temp is fine.

What could have caused the overheat?

Any help is appreciated.

[eherlihy]

I suspect that something is blocking the raw water intake. Maybe not completely, but something is in there.

Close the seacock, then open your raw water strainer. Clean out any junk. Leaving the strainer open, open the seacock. does water flow out as you would expect, or is there less than you would have thought?. If less, then the problem is the line to the strainer, the seacock, or the through hull (you don't have a strainer on the outside of the through hull - do you?). If water flows well, clean up the spill, then check the line from the strainer to the pump, and the pump itself.

Because you seem to say that at one point water flow stopped completely, I do not suspect your heat exchanger.

[eherlihy]

And for those of you who don't know why many people dislike external sea strainers;

Take a look here:external_strainers

[glassdad]

Eherlihy: Thanks for the input. When I opened the salt water pump, water flowed in fairly freely. I don't have a strainer in the line, only an external strainer. I think I must have had a blockage there. I will ask my dive service to clean it well.

Thanks

[celenoglu]

The output end of salt water can also cause similiar problems. some debris from salt water intake or exhaust might cause blockages.

[LakeSuperiorGeezer]

Originally Posted by glassdad

...I checked the oil and it read low. The next day I went down to change the oil and checked the level first. It read full but it was dirty...

What color was the oil? If it was gray maybe with some brown in it, it could be water in the oil. That would explain the level being low and the next day high, water getting into the crankcase. Also, over heating is a symptom of exhaust gas getting into the cooling system. Go to your local auto parts store and get the tester for carbon dioxide gas in the cooling system. If so it could be a warped head or a corroded head gasket. It could also be a crack in the head. A crack in the block is unusual unless it is an old flat head (L head) engine.

[glassdad]

The oil was black. No brown or gray. It was a little overdue for changing. I try to change it ar 50 hours. It was about 70 hours.