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can blown head gasket cause low/no oil pressure? 1999 7.4 L

stuffdogg

New member
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.
 
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Re: can blown head gasket cause low/no oil pressure?

Put a mechanical gauge in place of the sender to see what pressure you have. Also ask your friend what the h...l he did to your engine when it overheated; keep driving it? He may have run it hot and destroyed the bearings--no oil pressure now.
 
Re: can blown head gasket cause low/no oil pressure?

Friends don't let friends drive their boat or they won't be friends for long!

Do like Guy said. it's possible the oil Pressure sending unit fried when the block over heated. Also if the oil passage at the gasket was breached between the oil and water jacket would affect your oil pressure as well but not totally.
 
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Re: can blown head gasket cause low/no oil pressure?

The friend said nothing was out of the ordinary, they did not go far and boat was fine when they docked it. But you know how that goes.... Whatever! I don't think the sending unit went bad as it was working when I first got it started then when it warmed up and started running a little hot it read zero. when i get back over to the dock i plan on hooking up a manual pressure gadge to check it. I have read that the water mixed with the oil could thin it out to lower the oil pressure. also i noticed that the pressure rating for this engne at idle is 4psi. Seems logical to me that the water mixed with the oil could lower the pressure another few psi and Im sure that that gauge is not that sensitve and like 1-2psi might as well be 0 to that gauge. but what worries me is that it when i reved the engine up to 2000 rpm the pressure did not build, still 0. Ill go back over this week sometime to tinker with it again. im just hoping the combination of thin oil and oil leaking out of the head gasket is causing the low oil pressure. I just wish i could rule out worn bearings. :(
 
Re: can blown head gasket cause low/no oil pressure?

Engine bearings don't like water. Your friend probably was not paying any attention to the engine gauges while enjoying your boat. With all due respect, you can't blame your friend for the damage since he is not a serious boater.

I assume you have pumped out the old oil by now. Fix the water pump. Pressure test the block. If it holds pressure then pull the manifolds/risers and inspect them and the gaskets for damage, cracks and blockages. If you find the water injestion problem there then you may be able to salvage your engine. If all is well then you'll need to pull the heads.
 
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