Weird Engine Overheating Problem ...

[bobconnie]

Just for Giggles, ck the thermostat in water on the stove, put in a pot and cover with water,heat the water and see if it OPENS before the water boils, ive had Many defective thermostats over the years, also the cking of the tubestack is where I would go after cking the thermostat. it's been the 2 most trouble prone spots in the cooling systems Ive had or worked on over the yrs just my 2 cents Bob and Connie

[Seahunter]

Originally Posted by sneuman

It's an Isuzu Pisces. A marinized forklift engine - 4cyl, 55hp.

This is the similar engine to the Hans? Is the heat exchanger marked with the word "Pisces"? If so, you can access the tubestack by removing the 8 bolts from the front of the heat exchanger.

[sneuman]

I should say the heat exchanger was rebuilt recently. I also cleaned out the mixing elbow a few years ago.

[delmarrey]

Originally Posted by Seahunter

Mixing valve or exhaust elbow or riser all Googlable

Tube stack or heat exchanger tube stack or heat exchanger also Googlable.

[/B]If raw water has been sitting in the lower end of the heat exchanger there's no doubt corrosion. Corrosion leads to failure and leaks.

Must have different terms on the East Islands. Been repairing/replacing cores/elements most my life. Stack tubes were in the boilers. And a valve would open and close. I would think an exhaust elbow would be called an injector nozzle, if anything. But one learns somp'n new everyday. That's why I asked.

[Arch Stanton]

One of my local San Juan 28 sailors had an overheating issue that vexed him for several outings. It turned out to be a coolant hose caving in when it got too much vacuum.

[cal40john]

Originally Posted by donradcliffe

Please confirm that you meant mixing elbow when you said mixing valve--the OP's problem is with his engine, not his shower.

I think mixing valve = thermostat after some googling and guessing.

John

[cal40john]

Originally Posted by Seahunter

I also stated, exhaust elbow and riser; but yes "mixing elbow" can be thrown into the mix. However, I doubt if this is the problem. The more I think of his description makes me think that his tubestack has failed. It's probably plugged up so bad that raw water can hardly pass. The only water exhausted is from the bypass to the riser and is pumped overboard (making it appear as if water is getting through the heat exchanger), while the engine over heats, the coolant pressure rises, squirting out pinholes in the lower tubestack and out the exhaust. This would account for the coolant loss, as well as the overheat. One could pinch off the bypass to riser hose with a pair of vice grips and see if any raw water is making it through the tubestack. You'd have to be quick so as not to damage the exhaust system with overheated gases.

How common is a bypass on the raw water side of a freshwater cooled engine? Mine doesn't have one nor do the engines of my friend's boats, but that is probably a sample size of <10 that I've looked at in enough detail to notice.

John

[delmarrey]

Originally Posted by sneuman

I should say the heat exchanger was rebuilt recently.

Now that you've mentioned that, there could be a possibility that fresh water is passing by the new H.E. core seals.

Did this problem start after the rebuild?

Originally Posted by Seahunter

One could pinch off the bypass to riser hose with a pair of vice grips and see if any raw water is making it through the tubestack.

Not sure how one could do that w/o having a clear exhaust hose or dumping water in the boat.

[hpeer]

I had a weird problem on my little Volvo MD4A.

It would run fine for hours and days. Then suddenly overheat. Raw water cooled but that may not matter to the solution.

This went on for four years. Drove me nutz and nearly ruined my sailing fun.

An old grizzled salt finally came to the rescue.

I had a fitting that required a copper compression washer. It was in the line from the transmission to the engine. When they rebuilt the engine they omitted the copper washer and used silicone instead.

Normally it would work fine, but once in a while it would develop an air leak and stop pumping. Then self heal. Then fail again.

I didn't even know I didn't have the right thing since I had not seen it put together correctly and I'm a novice on much of this (but gaining experience daily.)

Replacing the copper washer was all it took.

Insidious to be sure.

I would go back over all my fittings to assure that all is according to Hoyle.

Almost every issue I have had with the engine can be traced back to the rebuild and them taking some short cut. Maddening.

I once had a boss who would always say ..... "If there is a new problem find out the last place someone worked and go see what they messed up."

Good advice.

[sneuman]

Originally Posted by delmarrey

Now that you've mentioned that, there could be a possibility that fresh water is passing by the new H.E. core seals.

Did this problem start after the rebuild?



Not sure how one could do that w/o having a clear exhaust hose or dumping water in the boat.

No, the overheating problem was why I had the heat exchanger worked on.