Hi all,

I have a 98 4.0L that is losing engine coolant, but it is not leaking. Over the past eight weeks the coolant in the overflow tank has slowly gone down, and is now gone. I'm thinking lower intake manifold gasket, but did a compression test this morning to make sure it isn't a head gasket.

Before starting it this morning, I did pull the plugs just see how they looked. The first one out was wet, the rest dry. The compression test showed the cylinder that had the wet plug had lower compression, about 15 pounds lower ( it was 140 the rest about 155). So now I'm wondering if I have a blown head gasket, any opinions on this?

If it is the head gasket, wouldn't I have to replace the lower intake manifold gasket anyway?

Thanks in advance

 

Check out this thread...

https://www.ford-trucks.com/forums/s...d.php?t=232373

 

I had seen and read that thread previously. That is what made me think it was the lower intake gasket. I should have included in the original post that the truck has been pressure tested, and passed, when it starts after sitting it will stumble a bit then run fine. There are 95K on the motor.

I was already to tear into it and replace the gasket this weekend, when I decided I should check the compression, and the one cylinder being lower than the others by 15 lbs makes me wonder if there could be a leak in the head gasket? I would like to avoid doing this twice.

 

Your symptoms sound almost identical to what I had with my 4.0L. Mine also passed several cooling system pressure tests that I performed on it, and showed no leak down at all when I tested the compression in each cylinder. That’s why I leaned more toward it being an intake gasket problem. Except for the reduced compression in cylinder # 4 (along the same lines as what you have), the cylinders overall seemed to test out OK, and I wasn’t getting any white smoke out the exhaust, no overheating issues whatsoever, none of the usual signs of a blown head gasket. It was pointed out to me that often times coolant leaking into a cylinder over time will have the tendency to “cleanse” the cylinder of carbon, hence lowering it’s compression, as measured against the other cylinders.

If you suspect more than an intake gasket problem, than I would be more inclined to think it is a cracked head, as opposed to a head gasket, based on all the info that I have come across on the subject. So if you go for it and replace the head gaskets, make sure you have the heads professionally tested while you have them off.

FWIW, a few weeks ago I had the opportunity to do another compression test on my 4.0L, and the # 4 cylinder still shows somewhat less compression than all the rest. But here it is 6 months later and my 4.0L is running fine.

Which cylinder is giving you problems?

 

Thanks for your post.

I believe the cylinder with the lower compression is #4 (front of engine drivers side). Given what you said in your post I'm more inclined to belive that it is just the lower intake gasket not the head gasket. I don't have any problems with white smoke or overheating.

So I think I will replace the lower intake gasket and see if that solves it, if not then I will have to look at replacing the head gaskets, and having the heads inspected. Hopefully that doesn't happen.

Thanks again for your info. I have printed out your PDF file on replace the lower intake gasket, that will be a big help.