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Engine overheating and coolant is gone

D

deco_stop

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"I have a situation with one o

"I have a situation with one of my engines and can't seem to figure out the problem. I have a feeling my worst fears are going to be answered in this post so here it goes. The engine is a Mercruiser 3.7LX (1989) sterndrive with Alpha One outboard. The inboard is GM, and 180hp. I have been having an overheating problem which started out kind of slow and got progressively worse. Basically the engine started to overheat after about 5-10 minutes at 3000 rpm and 20 knots. I replaced the water pump and impellers and it still overheated. Then I was told it was the exhaust manifold, so I replaced that but still it ran hot and the coolant would just seem to disappear and no remnants of coolant in the bildge. I did have what looked like water in the oil (milky) but then after a day when the engine cooled the oil looked fine. Then I was told it was the heat exchanger, which I just replaced...and again it overheated after only running 5 minutes at 15 knots. Again the coolant resevoir seems to be dry, and water in the oil. Now I am told it is probably a cracked head or block or if I am lucky it may be the head gasket. Any help would be greatly appreciated, because my next choice is to make this boat the next artificial reef in the Florida Keys.
angry.gif
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"Walt;
If the coolant is disa

"Walt;
If the coolant is disappearing without a trace, that's not a good thing.
You have replaced the heat exchanger so that's not it. If your manifold is closed coolant cooled, it could have a leak to the exhaust and your coolant is disappearing that way.
Oops, just re-read your post and I see you have replaced that also. Scratch that idea.

About the only other place it can be going is into the combustion chambers thru a head or block crack, or into the oil through a gasket leak or block crack.
You should run a compression check and see how the cylinders look.
If you find one or more low, you could run a cylinder pressure check to see if you have a leak into the coolant from a cylinder.
You may get lucky and just have to replace a head gasket.
Do you run antifreeze in the coolant, and if so, have you noticed any whitish smoke? That would indicate coolant burning.
Good luck,
Rod"
 
"Walter
You have to be carefu

"Walter
You have to be carefull sometimes that you dont end up replacing an engine just because you have a set of crook points.

Thats an exageration of course but it sounds like you have just been replacing things using guess work and that is about the most expensive way to repair a problem you can possibly get.

If an engine is a closed cooling system type you can think of it like a car engine, if your car was overheating and loosing coolant with no signs of leakage you would expect it to be a head gasket or similar problem.

Same with your marine engine, now most repair shops would carry a test kit for testing for combustion gasses in the cooling system, it is a very quick and very accurate test and I am sure someone could have tested it for you for under 20 bucks.

Now getting that done first would have saved you a heap of money.

I guess what I am saying to you is that sometimes it is worth paying a reputable repairer for the correct diagnosis first before you start throwing your hard earned at a problem.

Cheers
Peter C"
 
"Believe me when I tell you th

"Believe me when I tell you that I do not want to spend a boat load of money (sorry for the pun)on unneeded parts, but I have spoke to a couple of marine mechanics that have actually told me to replace what I have replaced thus far. Each one thought they knew the problem but it did not help as we see here. We did do a pressure check on the coolant system and it proved no leaks, then we did a compression check with the results for each cylinder as 150,150,120,120. I was told that is ok. Once again I am not sure. Not sure if I mentioned that if I fill the coolant resevoir, the resevoir is empty after a day or so. For the test I used straight water, then after replacing the parts I ran a 50/50 mix and immediately took it in the water to test it and as mentioned earlier after 5-10 mins the temp read close to 220 so I immediately shut it down. Is it time to pay the $65-$100 an hour for diagnosis or should I remove the head and hope I detect the problem myself? Thanks again to all of you for your help."
 
"That is what I am hoping for.

"That is what I am hoping for. As Rod asked earlier, there is no whitish smoke coming out anywhere and the engine runs great up until a load is put on it. Is there a test that I can perform other than compression that will point me in the direction of a head gasket?"
 
Walter
It may not hurt to put

Walter
It may not hurt to put a bit of cooling system sealer in to see if it stops your problem.
Bert
 
"Walter
Get the cooling syste

"Walter
Get the cooling system checked for signs of combustion gasses as I suggested in my first post.

It will confirm wether or not you are getting combustion gasses into the coolant which will tell you if you have a headgasket or head problem.

You could probably buy the test kit yourself at a reputable spare parts supplier.

They are very easy to use, you simply run your engine, add the chemical to the test unit and suck up some air from the header tank of your cooling system.

If you are getting combustion material into the cooling system the blue chemical will turn a yellow/green colour.

A pressure test is not always accurate when trying to determin an issue with a head gasket.

Over the years I have used these kits to probably diagnose hundreds of blown headgaskets.

Cheers
Peter C"
 
Thanks Peter. I will definatel

Thanks Peter. I will definately take your advice and get the cooling system check done. Hopefully that will point me in the right direction to finally put this problem to bed. Thanks again for all the help.
 
"Peter;
That's an excelle

"Peter;
That's an excellent suggestion and well worth remembering.
My daughter's turbo 3.0 liter I-6 Supra had similar symptoms about a year ago, and you could actually smell slight traces of combustion gases in the coolant overflow tank. Supras are famous for blown head gasket anytime over 100,000 kms, so we pulled the head, and sure enough.
Simple enough fix in the end, and like always; there is no problem that a liberal application of cash can't solve.
Thanks again for your suggestion regarding the test kit. That is a good one for future reference.
Rod"
 
"That's awesome. I had no

"That's awesome. I had no idea there was such a test kit for testing head gaskets. I am going to purchase one immediately and give it a shot, and maybe I will be closer to the cause and get my beloved boat back in the water. Thanks again and I will post back with good news. (fingers
crossed)Then the next pints on me!!"
 
Thats what we are here for.

Thats what we are here for.

Good Luck with it

I will look you up for a dive and a beer if I am ever in Florida
 
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