how to confirm a head gasket failure?

[fishingdan]

Hi,

I have been through all of the cooling system diagnostics and I'm down to, what I believe is now a head gasket failure. Can I confirm this with a simple compression test?

1991 4.3LX Mercruiser.

Thanks,
Dan

 

[bruceb58]

Re: how to confirm a head gasket failure?

Explain what you did with your cooling system diagnosis.

Also, what problems are you seeing?

 

[Haut Medoc]

Re: how to confirm a head gasket failure?

Hi,

I have been through all of the cooling system diagnostics and I'm down to, what I believe is now a head gasket failure. Can I confirm this with a simple compression test?

1991 4.3LX Mercruiser.

Thanks,
Dan

No, a compression test won't tell you anything.....
Is it a closed or standard system & what is the specific symptom/problem?......​

 

[fishingdan]

Re: how to confirm a head gasket failure?

Ok. Here is the story.

It is a raw water system.

Bought boat 2 years ago. A rebuilt engine was purchased and installed by the previous owner in 2000. The boat had a relatively low number of hours of usage from that time until I purchased it. Previously the boat was used 100% of the time in freshwater. I tend to use boats 80% in salt and 20% in sweet. Last year was 100% salt.

Last spring engine started to run warm per the boats engine temp gauge. Not knowing the history of the waterpump impleller, I replaced the water pump impeller. While performing that, I backflushed from the t-stat housing to insure water could flow easily from their, through the steering cooler and out the leg. No problem. A little sand came out. Put it back together, confirmed (visually) a good flow of water.

Boat still ran hot. At first only at higher speeds, but eventually it would climb at idle.

Again, not knowing the history of the manifold/elbows, I took them off to see what I could see. There were blockages in both (more port side than starboard). I replaced them.

The engine circulating pump is not leaking and I'm guessing that it is ok.

The t-stat was taken out and tested and it opens in the 140's if I remember.

The t-stat housing (checkball style), has no blockage and I confirmed water passing through as it should.

No water in the engine oil.

Per the merc troubleshooting guide, I seem to be getting to the point where the problem is narrowing down to other stuff. I don't remember exactly since I took a couple of months off during the winter, but I seem to recall that I'm getting down to head gaskets or some blockage in the block.

I'm just starting to think about this again and thus this post.

Thanks,
Dan

 

[bruceb58]

Re: how to confirm a head gasket failure?

I don't see how a head gasket failure should be causing your cooling problems. In a car, a blown head gasket would blow out your coolant but that won't happpen in a boat unless you have a closed cooling system.

 

[dpoff]

Re: how to confirm a head gasket failure?

Make sure to check the temp sender. Mine baffled me.

 

[zbnutcase]

Re: how to confirm a head gasket failure?

Could be exhaust manifold or riser issue. The cooling water flowing OUT of the engine is just as important as flow going in. And did you check the input side of the power steering cooler for blockage? And yes a head gasket can cause an open cooled engine to run hot as NO cooling system can deal with 1500deg combustion gases being forced into it. 'nutcase

 

[bruceb58]

Re: how to confirm a head gasket failure?

Could be exhaust manifold or riser issue. The cooling water flowing OUT of the engine is just as important as flow going in. And did you check the input side of the power steering cooler for blockage? And yes a head gasket can cause an open cooled engine to run hot as NO cooling system can deal with 1500deg combustion gases being forced into it. 'nutcase

He already said he replaced the manifolds/risers. I still disagree that the head gasket could cause a raw water engine to overheat. Think about it a second...how hot does a riser get and it is getting the same exact exhaust gasses!

If you want to confirm water flow, start the engine and take the hose off leading to the thermostat housing for a few seconds and verify your water flow. Do the same thing going into the manifolds.

Have you measured the thermostat housing with an IR gun?

How warm do the manifolds/risers get?

 

[fyrfightr]

Re: how to confirm a head gasket failure?

I would pull the engine water pump, just to be sure. I have seen automotive pumps used and the impeller completely rotted away....

 

[rodbolt]

Re: how to confirm a head gasket failure?

a leaking head gasket can and WILL cause a raw water cooled engine to overheat.
think about it, everytime it blows gasses into the cooling system its a big air bubble.
seen it been there done that.
however a leakdown test can easily pinpoint a leaking head gasket.
you may have to use some imagination blocking off the cooling water outlets and inlets,I use ballons and a rubber band,apply air and see if you can inflate a ballon by injecting air into each cylinder with the piston at TDC compression stroke.
on the riser ex gasses are inside the riser,cooling water flows in a jacket around the inner part of the riser and the gases and water are mixed downstream of the riser outlet.

 

[bruceb58]

Re: how to confirm a head gasket failure?

think about it, everytime it blows gasses into the cooling system its a big air bubble.

OK...I'll buy that!

 

[rodbolt]

Re: how to confirm a head gasket failure?

but typically your going to start noticing water marks or water droplets on the plugs.
burning water leaves tell tale marks on the electrode and porclen.
not hard to check but neither is knocking out a core plug and checking the block for sand.

 

[cr2k]

Re: how to confirm a head gasket failure?

We do our work here in central CA and the summers get hot. with an open cooling system we have seen the most nonsenscacal things cause overheating.

Things you never suspect even had anything to do with the cooling system.

A compression test is an easy free way to rule out the headgasket so why not?

 

[Aviator5]

Re: how to confirm a head gasket failure?

I had a 470 with blown head gasket. Neither compression nor leakdown test would confirm it. I could only see it when I pulled the head off. Motor would run up to 3/4 of the throttle with no visible or audible problems, only when I go WOT after a few minutes it starts pushing the coolant out of expansion tank.

 

[fishingdan]

Re: how to confirm a head gasket failure?

Thanks for the comments. I did gather some IR temps around the system and wrote them down, but I don't have them handy and will need to dig those up (taken in the fall).

I have been an outboard person for most of my life and I'm reminded why every time I look into the engine area. The bottom half of the engine is just so tough to get too in these I/O setups. My boat (Cobia Monte Carlo 193) has the after bench seat in front of the engine and a sunning platform over the engine (nothing unusual).

I would love to check the block for sand/crud, but that sounds like a bottom-of-the-engine adventure. I may end up pulling the bench seat to gain some access to the engine.

 

[cr2k]

Re: how to confirm a head gasket failure?

shouldn't take that long to remove the seat. Grab a power driver and go for it.

 

[Silvertip]

Re: how to confirm a head gasket failure?

A head gasket leak between cylinders can indeed cause an overheat. The compression stroke on the affected cylinders will have drastically increased combustion temperatures because that cylinder is filled with superheated gases from the adjacent cylinder. However, the diagnosis mentions warm on the temp gauge. How warm is warm and is the alarm sounding? Whether or not a compression test is of value depends on how serious the leak is - if there is one. But if you have the gauge, it costs you nothing to try. If the leak happens to be through a water passage into an adjacent cylinder that too can result in an overheat since water can pass into the cylinder turning it to steam on the way. Steam is at 212 degrees or warmer. A plug check can confirm that condition as they/it will look like brand new since they have been steam cleaned.

 

[fishingdan]

Re: how to confirm a head gasket failure?

Thanks for the feedback. I plan to pull the boat out, pull the cover and get at it again now that spring is near.

I do have a compression gauge and, like you said, it doesn't cost anything to give it a spin.

The last time I ran the engine, the dash temp gauge climbed past 185 and was still going up when I shut it down. I have my IR temp readings written down in the garage. I remember the temp readings being similar at some points, but I can't remember which cooling system component I was pointing at off hand. I didn't get anything done this weekend due my daughter's pre-season soccer tournament.

 

[sqbtr]

Re: how to confirm a head gasket failure?

I agree with checking the eng circ water pump, Blown gasket between cyls will also cause dropped cylinders and most probably backfires.

 

[fishingdan]

Re: how to confirm a head gasket failure?

I pulled the eng circ water pump today. Nothing unusual about it. The impeller looks to be in good shape, it spins freely without and resistance, noise from the bearing, and nothing is clogged.