Head Gasket question?

[calincoltsdad]

I know a head gasket can cause overheating in a car. But can one cause overheating in a marine engine even though there is no water in the crankcase. I have an enormous amount of steam coming from the oil fill cap almost like a steam engine it just boils out once its at operating temp. When I take the cap off the engine idles up an extra 100 rpm and lowers 100 rpm when I put it back on. What can be causing this? I plan on checking the compression Mon. Can exhaust be coming from a bad head gasket and pressurizing the cooling system by going into the coolant valleys? The engine is a 4.3L V6 yamaha. Raw pump is new, changed circulatory pump, I hope its the right one. The impeller looks different than the one that was on there, not sure if it is supposed to be a reverse flow or not. Had to get on that fits a 1966 chevy small block to match the one on the engine completely. Risers are clear, new therm. (140), both exhaust manifolds have small cracks on the bottom of them on the out side that have been patched with jb weld. I dont know what else to do to this engine.

 

[45Auto]

Re: Head Gasket question?

There definitely IS water in the crankcase of a marine engine. Only difference between a raw-water cooled marine engine and a car engine is that in a car engine the water is cooled by the radiator and recirculated, in a marine engine the water is pumped through the exhaust manifolds (mixed with exhaust gas to cool the exhaust) and replaced with new water from the lake (or ocean, etc).

Sounds like you might have found out why everyone on the forums recommends aginst buying a Yamaha I/O .......

 

[Don S]

Re: Head Gasket question?

There definitely IS water in the crankcase of a marine engine.

There shouldn't be.!!!!!!!!

There should be water in the cooling pasages of the block, but not in the crank case. Leakdown test and cooling system pressure test is the way to find what and where something is leaking. To answer your question, Yes, a head gasket can cause an overheat. But usually not the first choice on a raw water cooled engine.

 

[calincoltsdad]

Re: Head Gasket question?

OK i've been doing some research and found a cooling diagram on a mercruiser with the same engine. Lot less complex coolong system but same principle. I have 3 therm. housings. Top one has 2 hoses that go to the riser elbows, middle has ther. and has inlet from raw pump and outlet to circulatory pump. Bottom has 2 hoses on front to exhaust manifold and 2 on back to riser elbow bottom inlet. Riser has 2 elbows inlets for water. Mercs have 1. I dont think the water is exiting from the intake. If it does it is supposed to exit the intake and go up through the exhaust manifold and back to the therm. housing and out the top riser outlet when hot. My water is going in the lower riser outlet and coming down the exhaust manifold and into the intake. That's backwards if i'm thinking right. Should go up through the exhaust manifolds and then out. I will pull the hose off the circulatory pump and run the water hose in to see if I get water from the intake. If not the engine has new gaskets so I could have a coolant valley blocked off thats not supposed to be not letting it up to the intake. This crap make my head hurt. Anybody have any insight. I thought about selling and let someone else have this headache but i wouldnt feel right doing it.Click link to view cooling diagram.http://www.ishopmarine.com/ishop/jsp/AsplIsmCcatViewBase.jsp?&lvlCode=3&pCode=C0000191&path=YAM~A0000001~M0000017~C0000191&isFromCMS=false&hideAdd2CartButton=&isStandAlone=&is4CmsShop=&reqln=Unknown&reqem=Unknown&reqph=Unknown&reqFor=29&req4Browse=1&docId=&docName=&isForSupStore=true&cCatFilter=YAM&eCatSupFldr=supplier-110-050-YAM

 

[mkast]

Re: Head Gasket question?

This crap make my head hurt.

Get the Merxruiser maintenance manual for the engine.
It will show the coolant path.
Then you can stop guessing.
Do the cylinder leaksown test.

 

[45Auto]

Re: Head Gasket question?

Oops, was seeing "crankcase" and reading "block" .......

 

[calincoltsdad]

Re: Head Gasket question?

I've looked at the merc manual and seen how the coolant flow is. Mine is flowing backwards from the risers down. Do i have the wrong cir. pump?

 

[mkast]

Re: Head Gasket question?

Mine is flowing backwards from the risers down.

From the risers down to the water intake, or from the risers down to the propeller?
If your system "runs backward",where is the water intake?

 

[calincoltsdad]

Re: Head Gasket question?

I found out why i'm overheating. No water is coming out of the intake. Why I don't know, either the coolant valley in intake is blocked or circ. pump is pulling instead of pushing water through. Can you use a regular water pump off a chevy on these engines. I know the impleller are different but does a regular water pump push water into the block or pull it from the block?

 

[mkast]

Re: Head Gasket question?

What size engine is this?

 

[calincoltsdad]

Re: Head Gasket question?

4.3l V6

 

[Bifflefan]

Re: Head Gasket question?

Wel heres another thing to check. If your idle goes up when you take off the oil filler cap, then you may (probably) have an intake gasket leaking into the valley. It sucks all the pressure out when the cap is on then when you remove it you give it some more to breath. But on the up side it sounds as if all the other gaskets in the motor are in real good shape as they can hold a good vacum.

 

[calincoltsdad]

Re: Head Gasket question?

Cant figure out why i cant get water to circulate from the intake to the exhaust manifolds. Will any water pump from a sb chevy work? the blades are different i know.