Odd radiator problem

Okay, I posted a few days ago looking for a good source for a radiator. I got a few replies and those of you who helped out, thank you. I am going to replace it, but I have a question just to help me obatin a better understanding of cooling systems.

Here's the problem:

I have a coolant leak. I'm not quite sure of exactly where it is coming from, but the puddle is forming underneath the front bumper on the passenger side. Here's the oddity however...it only appears when the vehicle is turned off after reaching operating temperature. If I leave it sit and idle for a period of time (5-10 minutes, whatever), there is no sign of leakage. When I shut it down, 30 seconds later, the waterworks start. I can't understand why the vehicle would be leaking when pressure is released from the system, but not when the system is hot and pressurized. Any ideas, anyone?

I sincerely hope someone can clue me in as to what the hell is going on in there.

Thanks a bunch!

David

What year, engine, etc...?

Check your overflow bottle (see if it's full). How's the level in the radiator? You might have a bad cap that's allowing the pressure to escape and permit fluid to flow into the bottle.

Oops...I can't believe I forgot that...

2000 XJ Sport 4.0, 4wd, auto.

The coolant bottle is almost always empty.

David

Was thinking waterpump, but it's location is more center. I'd follow the hoses and ensure that they're all tightened up. Just did this on mine. Had a few that were loose and seaped a bit. Tightened everything up, and all was fine. Going through the hoses as well, may help you find which one is leaking if it is just one of the hoses.

your system stays pressurized as long as there is heat in the system.. the flow stops with the engine, but the pressure remains for quite a while. you really have to get under it with a flashlight and really get up in there following it. maybe its a slow enough leak that the airflow of the engine running dries/slatters/spreads it around enough not to follow the same trail as when it is not running? another option .. and a much safer one.. get ahold of a coolant system pressure tester.. it is a small hand pump with a guage attached to a fitting that will go where your radiator cap does.. crank it up and look for leaks on a cool/cold engine is ALOT more comfortable. and safer. pull off your fan shroud and electric fan and even your grill.. look at every posible corner of the rad and all the connections.. could be a crack somewhere that is temp sensitive and leaks when the material expands but not as likely as a simple loose hose clamp or cracked radiator tank..

i would check the hose that runs to your overflow bottle also your radiator cap.

i had a simuler problem with my 99 sport turend out there was a small pin hole on the passenger side that only leaked every now and than it slowly got worse and worse. when i replaced it the ac cooler we slightly bent in to the radiator and rubbing

Mine leaks in that same area, when i tore apart the front of my truck today for a different reason, I noticed that it was leaking from the draincock, which is on the bottom passenger side of the radiator. I simply tightend it and so far i havent noticed leaking. But its only been half a day.

Other than checking to see if your hoses are tight and secure to the radiator, i would say that it might be leaking where the plastic side covers meet the metal. They have been known to leak there on wranglers. I dont know about cherokees tho. you will have to look that up.

I appreciate the help guys. Being in flight school doesn't afford me a lot of time to take care of stuff like this, and now I at least have a direction to go in. Saves me from wasting any time. You guys rock, and I'll get back when i figure something out.

David

Also if you have the splash guard under there, that rubber sheet thing, the leak can be coming from almost anywhere. When my pump went a couple of weeks ago the symptom was coolant under the vehicle, where it was depended on what kind of level I was parked at. It was not until I opened the hood and really got down to it that I found it was coming out the weep hole in the pumps nose.
Also when you first shut the engine off the temp climbs about another 40* for a few minutes as the engine is still hot and there is no cooling circulation going on so keep that in mind.

An old shade tree mechanics trick for tracking down intermittent leaks. Get a spray bottle like used for Windex and the sort. Mix up a little water and put some corn starch in the water. Spray all the area and let it dry. It will be white. When the leak happens, it will either change the color or wash it off, so you can track it.