Best way to check for a blown head gasket

I recently replaced the water pump on my 92. (4.0 L) I noticed today that the coolant expansion tank had about 1" less coolant in it from when I filled it.

Could be just normal but a friend says - Guaranteed blown head gasket.

I started it up and he says he could smell coolant.

The oil doesn't look like "chocolate milk." I've had other cars with blown head gaskets that have that foamy, chocolaty look - don't know if that's completely applicable here.

I'm going to really watch the coolant level, but otherwise what else should I look for? Is there test?

TIA

Pull the plugs & see if one doesn't look right.

Leakdown test. A compression test will show you that you don't have a seal, while a leakdown test will help you figure out where. You apply air pressure to the cylinder, and if gages show leakage more than 10% you start listening at various places to see where the compression leak is happening (watch the coolant for bubbles, listen at the exhaust and intake, pull the oil cap and listen, ...)

That's the way I found my blown head gasket. Pressurized the cylinders to change the valve stem seals. And got bubbling in the coolant overflow bottle when putting air in cylinders 3 and 4.

Never thought of pressurizing the cylinders, good thinking.

I would say that no leak is acceptable, but if I'm only leaking a small amount am I doing damage?

Pulling the head is out of my league at this moment. How long should it take a mechanic / how much should this cost me?

Should the head be planed or does the gasket just get replaced?

river6822 said:

Never thought of pressurizing the cylinders, good thinking.

I would say that no leak is acceptable, but if I'm only leaking a small amount am I doing damage?

Pulling the head is out of my league at this moment. How long should it take a mechanic / how much should this cost me?

Should the head be planed or does the gasket just get replaced?

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A small leak will eventually turn into a bigger leak. I stopped driving my 91 as soon as I saw a little water in the oil. The head gasket was pretty easy to replace but I have been wrenching for a while.
The mechanic you take it to will check for warpage after he removes the head. There probably won't be any warping if it hasn't overheated.
Now that I think about it, have you checked your heater core? They are notorious for going out (my 98 is leaking) and will just spill out the bottom tube onto the ground.

river6822 said:

Pulling the head is out of my league at this moment. How long should it take a mechanic / how much should this cost me? Should the head be planed or does the gasket just get replaced?

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I wouldn't get ahead of yourself here.... If it were mine, I would first at least run a compression test (compression gaugess are pretty reasonable to buy, cheaper yet to rent) and see if that shows anything. Monitor coolant level in the reservoir closely. If you continue to use coolant and compression testing doesn't show anything, consider a leakdown test.

I'm going to put some cardboard under it tonight and see if there's anything leaking as well. I think one of my frie has a compession tester, otherwise I think the local PA rents stuff

river6822 said:

Never thought of pressurizing the cylinders, good thinking.

I would say that no leak is acceptable, but if I'm only leaking a small amount am I doing damage?

Pulling the head is out of my league at this moment. How long should it take a mechanic / how much should this cost me?

Should the head be planed or does the gasket just get replaced?

Click to expand...

Bear in mind you're sealing an iron ring - with a gap! - against an iron cylinder wall. And, you're not testing for leaks in the "intended state" of the system - in motion and under great heat. Throw in that valves are a steel/iron seal as well.

A small leakdown (due to the operating clearances between the ring and piston, the end gap of the ring, and the like) is acceptable, and there's no way around it - even "gapless" rings (the two-piece Total Seal units come to mind) have a static leakage of something like 1-2%. This "acceptable leak" will, in any case, decrease once the rings get hot and expand (which is why a certain end gap specification is required. If you don't have enough end gap, you get "ring wedge" - where the ring butts against itself and ends up wrecking other parts or just breaking into bits.)

So a small static leak is acceptable - a large static leak is something you should isolate fairly quickly. You may hear a bit of escaping air when you pressurise the cylinder and listen at the oil filler cap - this is normal. If there's a lot, you have a ring problem. You could also have a head gasket blown between the cylinder and the oil drainback on the pax side of the engine.

If you hear air rushing at the throttle body, the intake valve is not sealing properly.

At the muffler? Exhaust valve sealing.

See bubbles in the coolant? Head gasket blown between the cylinder and the water jacket.

Also be sure to listen to the cylinders to either side - air going into one cylinder and coming out the next one means you've got a head gasket blown between cylinders.

Hey 5-90 is this test done with each cylinder in top dead center? So test a cylinder, turn motor, test next cylinder in the firing order, etc. I've never done it myself but it makes sense.

The resivoir could just be low because as the system self-burps itself of air, it will draw in more coolant until it is entirely full of coolant and no more air can be burped...

Sounds pretty normal especially for replacing a water pump where the block becomes almost entirely empty of coolant!

I think your friend is a little too quick to jump the gun and scream "Headgasket!"

ALSO; as I walk through the parking lot where I attend college, I can smell "coolant" quite frequently passing by vehicles. I attribute this to open-cooling systems with a resivoir that isn't pressurized (like your Jeep) where the smell of the coolant is able to circulate with the air, etc...and besides, I'm sure when you replaced that waterpump you had coolant dumping, and didn't clean every inch of the motor and such where it spilled! That would be causing him to smell coolant too!

88xjlover said:

Hey 5-90 is this test done with each cylinder in top dead center? So test a cylinder, turn motor, test next cylinder in the firing order, etc. I've never done it myself but it makes sense.

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TDC, both valves closed.

I thought you pressurized it at BDC??

Course the one time I did try to pressurize a cylinder the motor kept turning over with any air pressure, I took it as a good sign and got drunk to celibrate having a perfectly good motor

Id say iot is just burping the system. I have near 100 miles since my rebuild and It's still burping it out.

take it to a shop and have them do a pressure test or dye test. they will then know where its coming from. it may cost your $20 to find out where its coming from but its well worth passing it bye then it is to not fixing it at all. very well worth it.

river6822 said:

I recently replaced the water pump on my 92. (4.0 L) I noticed today that the coolant expansion tank had about 1" less coolant in it from when I filled it.

Could be just normal but a friend says - Guaranteed blown head gasket.

I started it up and he says he could smell coolant.

The oil doesn't look like "chocolate milk." I've had other cars with blown head gaskets that have that foamy, chocolaty look - don't know if that's completely applicable here.

I'm going to really watch the coolant level, but otherwise what else should I look for? Is there test?

TIA

Click to expand...

Coolant in the oil, oil in the coolant, smell of coolant in the exhaust.... Don't wanna play Captain Obvious here, but seeing as how you just replaced the water pump, it would leave one to believe that you could have a leak somewhere. I replaced the water pump on my '94 and had a leak on the lower hose that would only show up when pressure was about max in the rad. How's the temps? Slight possibility you didn't burp it completely and it needed a bit more?

in2fords said:

I thought you pressurized it at BDC??

Course the one time I did try to pressurize a cylinder the motor kept turning over with any air pressure, I took it as a good sign and got drunk to celibrate having a perfectly good motor

Id say iot is just burping the system. I have near 100 miles since my rebuild and It's still burping it out.

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As I learned it, it's TDC with both valves shut. BDC usually has one or both valves open, so that's not much help - you need a compression seal to make sure you're not leaking overmuch.

Thanks for all the great input.

My cardboard test didn't work out w/ just one rock, so I'm trying 2 tonight. hopefully it won't blow away again

It hasn't lost anymore coolant, but I've only driven it about 15 miles.

Sorry to dredge up this old thread. I didn't want to start a new one and couldn't find an answer from searching even though I'm sure its been covered.

Is there any special way to rotate your crank? And when you rotate the crank, how do you know when the cylinder in question in at top dead center?