485 37L Losing Coolant amp Overheating After Rebuilt

"Just returned to the lake wit

"Just returned to the lake with a resleeved 485 motor. Motor ran quite well before the tear down, but lost oil due to blow by on the bad sleeve.

I rebuilt this motor at a local marine shop & carefully followed the shop procedures.

The engine runs great, has lots of power, but overheats quickly. The closed coolant reservoir looses approx 1/3-1/2 gallon of water per MINUTE. Where the @#$# is all this coolant going..? No obvious leaks in the plumbing. Oil looks clean out of the dipstick and clean in the filter. Freshwater impeller is new, and traced the flow out of the voltage regulator, through the heat exchanger and out the exhaust.

Can anyone verify my guesses..?

1) Cracked heat exchanger is allowing coolant to pass through the seawater section and out the exhaust.

2) Frost plugs were removed during the sleeving & cleaning operation, and i somehow missed this.. (no obvious leaks on the exterior engine)

3) Somehow all this coolant is slipping by the head gasket and being burned, but i don't smell any burnt coolant in the exhaust, and the butt dyno says it feels like theres decent power, although no compressor check yet..

Again, this isn't an exaggeration - the reservoir is empty after a quick test drive to the middle of the lake and back. Coolant stays in the plastic reservior - its always full, but appears to be lower than where i would assume it would be located.

Any ideas?"

"Ideas:

Sounds like #3 - a

"Ideas:

Sounds like #3 - a head gasket problem. Water doesnt always leak into the oil gallery or oil into the water. Did you take a close look at deck height after resleaving to see if the block/head surface was true?

If you are fresh water cooled, there is a litmos test strip to test for coolant in the exhaust. Used on cars.

By firtue of the volume of coolant you are loosing, it should be easy to find. Try pressure testing the cooling system to a few pounds with the engine off and see if the loss continuess. If the water was going into the cylinders, there will be water in the bottom of your oil pan.

You could always get a big tank of water and constantly pump water into the motor as you cruise"

"The sleeving operation was do

"The sleeving operation was done by a well known engine shop in the area, and the desk surface was tested for warping before replacing the head.

So correct me if i'm wrong - if i pressure test the cooling system for 14 psi, i should see one of four things:

1) Pressure escaping through the valve cover vent and through the oil dipstick if water is entering the oil passages. Also a large amount of water in the engine oil.

2) Pressure escaping through the spark plug holes or intake / exhaust manifolds, coolant entering the combustion chamber. Will plugs show symptoms of water / coolant being burned?

3) Coolant being forced through the seawater exit line leaving the heat exchanger.

4) A miraculous giant hole in a hose that i have somehow missed..

Although this wouldn't work for a slow leak, i would imagine at this volume it should be readily apparent where the coolant is going.

The engine overheats even when the reservoir isnt completely empty - could both symptoms point to different problems..?"

"By chance did you let anythin

"By chance did you let anything freeze over the winter? (I do not know your location) Are you sure that all the hoses were returned to the proper place? The exhuast manifold could have a problem.(crack inside,bad / mis-aligned gasket) If the hoses were not put back in the correct place,the exhuast manifold could have over heated when you first ran the engine and then received cold coolant when the thermostat opened and cracked. This is what I feel the problem could be. A cracked exhuast manifold.If your model runs the coolant and not the sea water through the exhuast manifold. It's not hard to place a coolant hose in the incorrect place. If you can,run it on a hose and see if there is any sign of coolant in the exhuast. Add some type of dye if need be. Are you building more pressure than normal in the coolant system? If you went by the book on the machine work I have to think you would have checked the deck of the block and the head. Plus if it runs as well as you say I doubt there is a head to block sealing problem. If the exhuast manifold is leaking,it could pass that much coolant very easy. This is hard to trace since you can not see all of the inside area of the manifold. Again if this was ok before it should be now but who knows? It is a freaken boat after all and strange things happen. Since there is nothing in the oil this is just about the only way for that much coolant to get out. It's the only place that the coolant can enter the exhuast system if nothing else is cracked or broken in the engine or heat exchanger.
I'd check the coolant hose routing since it is heating as well and make sure the thermostat is working. I assume you set the timing with a timing light. To much advance timing could make it run hot.

Hope this is of some help and that you find the cause."

I'll do some further inves

I'll do some further investigation this weekend and report back with results. Hopefully this will help someone else with the same symptoms.

-Check cylinder compression and leak-down. Check plugs for symptoms of burning coolant.
-Check exhaust stream and seawater portion of the exchanger for traces of coolant.
-Recheck oil for traces of water / coolant in the pan and filters.
-Pressurise the cooling system and check for leaks.
-Recheck timing and verify proper settings.

"Don't know your exact set

"Don't know your exact set-up, but can you locate an adapter to use a garden hose to pressure the system? This was how we found one on a friend's boat. (Bad freeze plug on the back of the block)"

"Questions
1, Did you replac

"Questions
1, Did you replace the exhaust manifold?
2. Did you replace the riser?
3. Does it leak out on the hose in the yard?

Checks
1. fill res at rest and let set overnight. Next day pull # 3 and 4 plug and crank engine. Look for coolant. If so replace manifold gasket at least best to replace manifold and riser.
2. Top off res. With engine cold an the house hose, diconnect the water exit line from the side of the riser and splice a hose over the side. run engine for no more than ONE minute (don't want to burn exhaust hoses) check for coolant coming out the exhaust. Catch some of the raw water coming out the spliced hose and check for coolant. This will isolate the two systems and allow you to troubleshoot better."

"The manifold and riser are th

"The manifold and riser are the originals. I hadn't touched the coolant levels in the three years i owned the boat, and there were never any problems with the cooling system. But stranger things have happened...

The boat is currently on the lift, so i'll have to raise it out and run a hose to the dock. But your checks make sense - I'll do both this weekend."

"Back with results:

Cylinde

"Back with results:

Cylinder compression: 120, 125, 125, 90

On second look there were traces of water in the engine oil, enough to give the oil a milky white appearance.

Removed the exhaust riser and manifold. The exhaust manifold has a crack running vertically in the metal seperating the #4 cylinder exhaust passage from the #1-3 passages. However, the portion seperating the coolant passage from the exhaust passage appears to be ok, but i'll look into this further.

Removed engine head and head gasket. The gasket between the #3 and #4 cylinders appeared to have the gasket material burnt off. The gasket is a thin layer of metal covered by some type of gasket material. (Would a full metal gasket form a better seal...? ). The gasket material is burned and leads a path to the water jacket, but its not an obvious failure.

Any further checks with the head and manifolds removed from the engine?"