can bad head gasket cause low/no oil pressure?

[stuffdogg]

ok so we have a cruiser with a 7.4 454 mercruiser (1999). we let a friend borrow it to go fishing. The next time we went to use it, it was hard for the starter to turn it over, checked the oil... no signs of water in the oil. I've flooded many engines to know it was hydo locked. so i opened the throttle wide open and after a few spins it started up and i thought we were in the clear. oil pressure looked good so let it idol a few minutes and noticed the temp was getting higher than usual and a warning alarm went off near 200 deg so I shut it off and let it cool a bit. It would fire right back up and run smooth I then noticed that it had lost all oil pressure. so i killed the engine and checked oil again. this time found milky oil. So i figure it is a blown head gasket due to an overheat because I think the impeller went bad. Ive worked on many head gaskets but Ive never had a head gasket problem where i have lost ALL oil pressure. So is it possible that all my loss of oil pressure is due to major head gasket leaks or do I have a bigger problem such as bad bearings??? Thanks for any advice.

 

[Philster]

Re: can bad head gasket cause low/no oil pressure?

Here's my take.

If a head gasket leaks, it shouldn't get so much water in the combustion chamber(s) that a huge amount gets by the rings making the the oil milky. BUT...It can do that. It IS a possibility.... it just has to go on a while and/or be really bad and/or be working with some other issue.

Milky (watery) oil is going to be thin....and I'd expect it to drop the oil pressure like a stone. It can squeeze past things.... and that means low pressure. heck.. it will be lower than 2psi... which is essentially zero to a gauge.

Do you boat in salt water? Corrosion is lightning fast w/ leaks into the engine.

If water gets into the combustion chamber, the tiniest am't of corrosion can let things get past the rings.... into the oil... where the oil gets thinned out and now you lose pressure (lubrication) and water continues to wreak havoc on the combustion chamber....


How about your manifolds and risers?? They are the leading suspects any time a fair am't of water gets into the engine. And they are good for a few years in salt/brackish water. In very clean fresh water, they can last over a decade (easily).

This discussion must consider them.

 

[stuffdogg]

Re: can bad head gasket cause low/no oil pressure?

thanks for the reply. makes sense about the oil thinning from the water contamination.

I only boat in freash water lake. Im a car engine guy and new to marine engines. Are the manifolds and risers water cooled in this engine?? can they go bad from an overheat or can they cause an overheating situation??? Im going to try and tackle this repair myself but i need to be able to diagnose all possible problems. Thanks for leading me in the right direction. as of now im thinking impeller, head gaskets, machine the heads. I guess i do need to do a compression ck.