Hello everyone, I'm very new to the Jeep community. In fact, I'm 17 and have never even owned a car.

Yesterday, however, I was looking into buying a $600 '87 Cherokee that had a coolant issue. I went to look at it and after it ran for about 10 minutes the coolant bottle began to fill up and then coolant started erupting from around the cap. What I want to know is, apart from the leak, is this is a normal-behaving system (the complete filling of the bottle and the high pressure) or would I have a bigger problem than a cracked cap to worry about, such as a blown head gasket or something else?

Hope it's an easy fix, I want to buy this beauty and start fixin'er up!

 

Idk about the blown head or anything but it being an 87 you do have to replace the cooling system... anywhere from 100 to 300 for new,radiator with hoses ect

 

Yeah I've seen a lot on converting the system and that's one of the first things I'll do if I get the car. I'm aware that it's a pressurized system, but is what I'm dealing with just a simple leak in that system or is it's behavior abnormal and indicate something else?

 

Check the theromstat that might cause it.. hoses could be warn it could be lots of things.. you are only paying 600 for it so u get what u pay for

 

Any luck on it?

 

As said you might be able to fix it by putting a thermostat in it, or you may be looking at pulling a head off, so be careful. It might be worth finding a local mechanic to look at it, and see what's going on, then deciding to buy or not if you are not comfy with trying to diagnose this yourself yet.

 

Welcome

 

I apologize for not updating. I was ready to buy it and try some of the suggestions on this thread, but it had already been sold, and now I'm continuing my Cherokee hunt.

 

It's all good man good luck on the hunt tho

 

It is not.

Probably the most common cause of "drastic sudden boil-over" like that is really quite simple - a gas pocket forms behind the thermostat for some reason - typically due either to a prior overheat (find & correct the cause) or improper filling after service (air gets trapped behind the thermostat.)

If the thermostat is not "wet," it will not sense the coolant temperature and will not open.

There are two ways to purge air from the system:

- If the system is assembled and closed, jack up the rear axle until the engine is tilted forward (rear end highest.) Remove the coolant temperature sensor at the driver's side rear of the cylinder head (7/16" wrench, use a six-point so you don't accidentally round off the brass) and add coolant at the bottle, slowly, until you see it come out the hole where the sensor was. Replace the sensor (lubricate it with never-seez if you like, but PTFE is NOT recommended. It is a self-grounding sensor) tightening 1-2 flats past finger tight. Lower the vehicle, monitor coolant temperatures for the first few days of service.

- When replacing the thermostat (which you need to do anyhow, if it's been overheated. One overheat effectively wrecks the thermostat,) drill two 1/16" holes in the flange, 180* apart. Install the thermostat with one hole at 6:00 and the other at 12:00. The system will purge itself of air during operation, the bleed flow through the two holes will not cause any harm (I have done this on my 1987, my two 1989's, and my 1990. My 1988 doesn't like a thermostat, so I don't run one. Eliminating the thermostat should only be a measure of last resort!)

I prefer the second method whenever servicing the cooling system, since it requires no future intervention beyond monitoring the coolant level (which you should be doing anyhow.)

Most common cause for overheating is the thermal fan clutch, I find they're only good for 5-6 years before they want replacing. It's cheap enough and easy enough I just do it every five years - when I install the new one, I write the date on a fin with a Sharpie pen so I can read it easily as part of an inspection. There's usually a spare in a box on the shelf.