Car coolant question (need answer kind of fast)

I have a 2002 Jeep Grand Cherokee 4.7 HO that overheated whe idling. I just got some bad new from the shop, the coolant “foamed” and clogged the radiator and burned out the bearings in the waterpump. They asked me if I had put any additives in the coolant but I had not. They said they’d get back to me, but there only theory is the impeller in the water pump might have broken and caused the foaming. Any thoughts what may have caused the foaming?, I just don’t want to replace the parts and have it happen again and at this point the shop (a Jeep dealer) doesn’t seem confident in the root problem. And is the heater core likely bad now too?

While I’ve certainly come across clogged radiators, I’ve never heard of coolant “foaming” as being the cause. In the 10 years you’ve owned the vehicle, how often have you flushed the system and replaced the coolant?

Coolent was flushed and replaced two years ago with the heater core. I’m the third owner and the records I got were spotty so I’m not sure of it’s history

Maybe by foaming they mean cavitation?

Coolant cavitation can hapen when there’s too little ethyl glycol in the coolant (or straight water is used). The coolant boils localy near engine hot spots and bubbles form. Bubbles do not transfer heat well so the engine overheats. Also the pump cannot move efficiently bubbly coolant which makes the overheating problem worse.

foamy coolant in my experience is usually a sign of a blown head gasket or cracked head.

Straight water is actually a better coolant than 50/50 antifreeze. You can run straight water if you want. You’ll just need to add a “water wetter” (redline or RMI make a good ones) that lubricates the water pump. Just don’t forget to add antifreeze before winter comes. I run distilled water in my car ('87 Grand national) 7 months out of the year.

If you have oil in your coolant, it might cause it to foam. I would suspect a dealer would have easily diagnosed that though.

Do you know what type of coolant was added when the flush was done? Your Jeep should use a HOAT coolant, (Hybrid Organic Acid Technology).

There have been some problems reported with the similar OAT (Organic Acid Technology) coolants such as the DEX-COOL used in GM cars. These coolants should not be blended with regular glycol based typically green stuff.

But of course if the system has been flushed you can change to the green stuff without problems.

The other problem, and it may be the cause of yours, is that it is very important with these new coolants that all of the air is bled out of the system during a coolant change. It isn’t just a matter of draining, flushing, and pouring in new coolant. There are procedures for bleeding all the air out and they are important.

If a Jeep dealer did the flush then they probably did it right, if someone unfamiliar with HOAT/OAT coolants did it then they may not have been concerned about the air, or may have blended coolant types.

I’ve never heard of coolant foaming. I can’t make any sense of a claim that foaming coolant could clog a radiator, nor that a broken water pump impeller could cause foaming. I suspect they’re using the wrong word, and I wonder just what they mean.

If the radiator is indeed clogged, then it should be replaced. Rodding it out or recoring it doesn’t save much money, and leaves a radiator with old materials that may be deteriorating. If there’s some detectable gunk in the system that caused clogging, it may have affected the heater core. However, I’ve seen radiators clogged with the heater core doing fine, and heater cores clogged with the radiator doing fine, so there’s not necessarily any correlation there.

If the water pump bearings are faulty, the pump needs to be replaced. The old pump’s impeller can then easily be inspected.

The real question is why did it overheat. Faulty fan clutch? Thermostat? Water pump? Low coolant? I wouldn’t expect a clogged radiator to cause overheating at idle if it didn’t cause overheating running down the road. I suspect something’s been overlooked.

I got word back from the shop- this time they describe it as “gummy”, not foamy. Near as they can tell someone poured some stop-leaks in, either a shop when I wasn’t looking or a previous owner- I didn’t nor did I ever authorize anyone too- the original, since replaced heater core had leaked at some point when it was replaced. Head gasket and block are fine. Heater seemed weak last winter but I’ll deal with that later if it’s still a problem, hopefully a system flush fixed it.

Now that sounds more realistic/logical.