4.0L engine, 221,000 miles, is going through coolant to the tune of 1.5gal monthly. Suspect a head gasket or cracked head.

A forum seach on the topic reveals all sorts of telltale signs but this engine does not display any of the classic symptoms -no milky/cloudy oil or oil in the coolant - no smoke or odors from the exhaust, no leaks under the vehicle.

No rise in the temp. gauge until coolant nearly empty. Heck, it idles fine, runs smoothly and continues to get 18+ mpg at its advanced age.

How could it go through this much coolant without any evidence? If the head gasket were leaking wouldn't there be an accompanying pressurization of the cooling system?

 

Wow, with that kind of loss you'd think it would leave a trail. I was thinking with that kind of milage maybe you have a freeze plug leaking, maybe on the back of the block, but that should leave a puddle or trail or....something.

 

earlier 4.0 had intake manifold gasget leakage problems. They have updated the gasget. Look at the top of the transmission at the rear of the engine area for trails running down.

 

Thanks for the replies.

The original post obviously offended the Automotive Gods and I am now suffering their wrath. Within 24 hours after posting, the engine is now acting up.

Looking back, I had a very slight frontal vibration that I took to be from a cold front end differential that would resolve after warm up. That vibration has worsened and is now definitely associated with the engine(misfiring) as well as a pinging and knocking sound under slight acceleration. (Distinctly different from eroded plug wire ping/rattle.)

Curiously, there still is no smoke or odor from the tailpipe. These newest engine noises have me convinced there is a problem with the heads. I will check the intake status but all was dry the last time I checked the rear engine area. Given the volume of coolant being consummed and lack of leakage it has to be going out the tailpipe. I'll keep my fingers crossed that it may only be an intake manifold problem.

 

Sorry to hear that. It is sounding like a head. Have you looked at your plugs for any coolant?

 

stepman,
I changed them earlier this summer and did notice one (#5, center) had small amount of fluffy deposit on it I did not see on the others. I wasn't sure what to attribute it to at the time, but in hindsight perhaps that was an early indicator. I'll be tearing it down shortly and take another look at those plugs for confirmation.

 

I hate when that happens. I think you had an idea where this was going all along, you just didn't want to go there.

 

Update:
Took Homer's suggestion to check the lower intake manifold bolts. There was no obvious leakage at the rear and rechecking #5 sparkplug revealed all well there, no deposits which surprised me, given how poorly the engine was running.

None of the manifold bolts appeared to be obviously loose but I retorqued them to be sure. Two days of driving now finds the engine running normally again with no stumble or mis-firing as previously. It is too early to tell whether or not this cured the coolant loss. I'll keep my fingers crossed it has.

 

Just something to think about, but my truck was loosing coolant somewhere. Ended up leaking out the water pump, it would wait about half an hour after shuting off the motor then start leaking. I still can not figure out why it would wait, other than it didn't like me at the time. It may not be the case for you but, just something to think of. Good luck.