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Intake gasket or cracked heads?


January 24, 2006
Reaction score
City, State
bremerton , WA
Year, Model & Trim Level
1991 LT
I am loosing coolant some where but not sure where. I replaced the pump, radiatior, thermostat, and hoses. There is no visible leak anywhere-not even a little coolant on the engine it self. When I first start up in the morning it has a rough idel and goes away after a few seconds and runs fine from there without a hint of trouble. So when the thing warms up i'm asuming the coolant stops leaking. But not 100% sure of that.

I know that the intake manifold gasket is a big problem area and so is the cracked cylinder heads. But what is more likely to cause coolant to be burned in the combustion chamber? The leaky gasket or the cracked heads? Should I plan on replacing the manifold gasket and go from there?

The Ex is a 91 XL with 180,000 highway miles on it. Always been taken care of and NEVER overheated.

Thanks for the replies!!

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Do a compression check on all cylinders, or a leakdown test. Also I would try having someone sit in the drivers seat and hit the gas a few times when the motor is cold but running and see what comes out of the exaust. Other than that check your radiator and hoses. If it has NEVER been overheated, I would look past the heads, only problems out of mine have been since it has been over heated, and BAD. Good luck!

Well if you are replacing fluid every few weeks or so then I would say look at your radiator. Mine would always leak down to a certain point and then stop at that level which was about a 3rd of the way down in the raqdiator. The plastic tanks on the side of the radiator sometimes leak where they join with the metal. My leak was so small, that I did'nt notice it until a realy hot day and I was checking my AC and noticed a tiny wet spot on the top of the radiator passenger side where the metal and plastic meet. Problem solver with a new one.

I have done a compression test and all the cylinders were around
180 +/-4 PSI. I have not done the leakdown test yet because the Compression test doesn't show any indications to trouble.

I don't think it's in the cooling system, as the radiator, pump, hoses, thermostat and even the heater core have been replaced. I have replaced all that as a preventative measure. good or bad, I didn't care. 180,000 miles and I just wanted to be carefull.

If I take the manifold off to replace the gasket will I be able to see IF it was leaking around the gasket? Or will the gasket be destroyedin the process?

Do the cylinder heads usually only crack if they have been over heated, or can they just crack from normal wear and tear?

Never say never. Just because parts are new doesnt mean they cant fail. The one time I saw a manifold gasket failure, the water was pouring out the back of the motor, but you should see some signgs of corosion if its leaking elsewhere. Changing that gasket is kind of a pain but doable in an afternoon. If the head was craked, chances are you would have milky oil, and a bubbling coolant catch tank and your exhaust would be steamy.

Also If your heads were cracked your compression in at least one cylinder would be considerably lower than the rest. If you are careful, you can remove the intake manifold gasket with out completely destroying it. I (i know it wasnt a good idea) reused one on one occasion. If I were you I would carefully inspect the entire cooling system, from cap to cap again. I would figure since work has been done it would mostlikely be in that area. Or you can try a can of radiator stop leak, and that might help too.

I don't know if this helps or not. Before I replaced all the external (to the engine) cooling components I had the same signs and symptoms as I have now(after replacement).

The only thing noticable is when I start her up in the morning the idle is a little rough. after a few seconds it clears right Up and no troubles at all while driving. Also I loose maybe a gallon of water every two months or so, nothing major.

I used a coade reader and the only code I had was for the MAF sensor. I cleaned that and re-ran the scan and no trouble code appeared.
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Josh, You recommended to check for signs of external leakage and there are none.

Is it possible for the gasket to only go bad towards the inside of the manifold and leak coolant into the comustion chamber.

In my head that would explain the rough cold startup in the morning. Then if it's a small leak it won't be as noticable when the engine warms up and operating at normal temp?
And that's why I'm loosing coolant mysteriously while having good compression numbers (not a cracked head)?

What do you guys think about my reasoning?

Well, that's possible. But as was said, I have seen many coolant leaks that were not gasket or manifold--they were leaking at the radiator, or the hoses, or both...and they were not noticed by the person. There were no whitish coolant deposits. The coolant was flying out the seams in the plastic/metal composite radiator tank, and not staying around. Also coolant would leak out the coolant hoses under certain specific conditions (cold day, warming up engine) and it was underneath the upper hose, and also thus was not noticed. Simply tightening the hose clamps (as tight as humanly possible) fixed that problem.

One question I have for you, that I might have missed in this thread: Are you seeing moisture on the underside of your oil filler cap?

Like I said, I did not notice mine until a hot day and just saw a tiny bit of steam leaking out of the seam. Try warming it up to operating temps on a hot day and maybe pour some water on the seams of the radiator and maybe you will see some bubbling or something.

Do a cooling system pressure test both cold and warm. Be careful when you relieve the pressure when it is hot. If it is a crack between the valves like I had it gets worse after it warms up. Look for not only a pressure loss but an increase also when you test it warm with the engine running. If you had access to a combustion vapor sniffer you could check it fast with the engine running and the probe near the radiator mouth. If you end up needing heads I have a new pair I will list for you.

It might be worth retorquing the intake bolts. I had some coolant burning, but couldnt figure out where, and retorquing the intake bolts pretty much stopped it. I believe they need to be torqued to 14-16 ft.lbs, but i would check on that. Theres an article on this somewhere, maybe TRS?

If it is infact leaking into combustion chamber, your plugs will tell you.

18 ft pounds on the Intake manifold hardware.

Don't forget the two Nuts that are hard to see. One that is very close to the Temp Sensor on the Front Passenger side and the other that is in the back drivers side. They are the most likely culprits since that is where the Water Jackets are closest to. Figures that they are the tough ones to get to.
The front one, you have to take the Upper hose off to get to. the hard pipe is directly over that nut.

Tony H said:
18 ft pounds on the Intake manifold hardware.

I tore in to it last night and got down to the fuel rail and stopped there. I thought i'd try tightening the bolts down on the lower intake manifold before replacing the gasket all together. The BOLTS were close to 18 ft-lbs, but the front and rear NUTS were more like finger tight.

Is this usually the problem? Do they just get loose over time or is it usually the gasket that goes bad?

Since I didn't feel like taking apart the fuel lines, i just re-torqued the fasteners to 18.5 ft-lbs for good measure. I fired it up and it seemed to run alot smoother.

I re-used the upper intake gasket as it looked ok.

I'll wait a week or two and keep checking the coolant level and see if i've fixed the problem or not.

Thanks alot for all the input!!!!


The gasket usually poops right there. That is where the water jackets are that come up from the engine to the intake. They weep a little and by the time you see it, it tore the gasket. I hope you have better luck ...I tightened them and it lasted a few months.
It gets pretty 'interesting' as you start unplugging all the Injectors and such. You do not have to unhook the Fuel lines from the rail, I lifted and rocked the whole mess up onto the Brake Booster. It stayed there long enough to clean the Gasket surfaces and get the lower manifold, and valve covers back on.