I'm trying to diagnose a mysterious loss of coolant (as well as poor gas mileage), and I was wondering if this is a normal occurrence.

After shutting off my engine the overflow tank bubbles for several seconds as the coolant level rises. Is this normal?

My plan is to have the oil analyzed by blackstone labs to check for coolant, since I have the 0331 head, but because I recently changed the oil they said it would be too early to tell anything, so I just have to wait for now.

 

I have the same problem but only in certain condition coolant is starting to spill over. Checkout my post , maybe there is something useful

https://www.cherokeeforum.com/f2/hel...0/#post1201803

 

Thanks a lot for the info. Mine never even comes close to spilling over. It only bubbles for 10 or 15 seconds a rises a few inches.

 

What year is your xj?

 

When you turn off your engine coolant isn't circulating or cooling anymore and the temp rises and coolant expands. Tis normal and the reason why you aren't supposed to fill the overflow all the way.

 

It's a 2000.

I thought this might be normal, but I wanted to check and see if anyone else might be having the same issue. I'm hoping there is a leak in the cooling system somewhere, because the only other candidate is a bad head gasket or (more likely) a cracked head

 

It might also be worth noting that since I got the truck in January I've gotten terrible mileage, about 11 mpg city, with a stock setup. Everything is in great condition except for the coolant loss and poor mileage. Could these two issues be related?

 

If it runs good and strong I'd say your ok. Take off the rad cap and start it and look for bubbles. It could also be the weep hole in the water pump. Sometimes they leak slow enough that you don't notice. If the gasket is blown ya you'll get bad mileage but it will run like crap too. A lot of times its due to a clogged cat or bad o2. Google vacuum diagnoses. That coupled with a compression test will tell you everything you need to know.

 

Thanks a lot for the tips Slick. I replaced the 2 upstream O2's but haven't noticed a difference since installation. I also did the water pump about 3k miles ago so I hope that isn't the issue. My guess is that the coolant is leaking in a spot that causes it to evaporate immediately, so I'm not able to trace it. Might give the cooling system pressure test a go as well.

 

Good idea. Pressure test may reveal something you havent seen. I had multiple little issues with mine that would cause it to overheat basically randomly. I had a crack in my resivor (take in mind I have a ****ty closed cooling sytem) which caused air to get in the lines. I had a small slit on both the upper and lower rad hoses. And my fluid was dirty as poo.