boiling over

[THRASHER]

i have an 87 with the 4.0/aw4. it will idle for about 20min or drive for about 5 at low speeds before it boils over out the overflow and blows the cap off of it, I have...

wired the fan to a relay, its always on if ignition is on

drained the radiator and ran water through till it was clear, no sign of rust
filled with straight water now till i can figure this out

pulled out the t-stat

new cap on the overflow bottle

any ideas on what else to check? the temp on the passenger side of the radiator is around 270 when this happens and the driver side will be around 160, water drains out of the overflow while running then comes back in real fast if engine is shut off.

 

[5-90]

Sounds like you're in decent working order. What flush did you use, before you checked for loose rust? There could be rust in the system that isn't loose.

I'd also highly suggest adding Water Wetter - the stuff does work.

Is it also fairly safe to assume your lower (suction) hose isn't collapsing? Does it have the "spring" in it? Something else to check.

And, how's your fan clutch? You don't mention it, and it's a significant contributor to radiator airflow. If it's shot (3-4 years old, tops,) think about changing it. When you do, take a marker and write the date on it - it's a good habit to get into, and it saves you talking to yourself wondering when you changed it last (I do that with most of my maintenance parts...)

5-90

 

[Johnny V]

And, how's your fan clutch?......If it's shot (3-4 years old, tops,) think about changing it. 5-90

Geez my '89 has it's original fan clutch. Stays under 210 even in 90 degree weather. Not sure if I should touch it!?

Anyway regarding the boiling over...had that problem last year after replacing all hoses and water pump in my '89. Turned out there was air in the system. Do a search on how to purge the cooling system...but basically have the jeep's rear up in the air a little, either jack it up or place the rear tires on the curb. Fill the bottle halfway and with the engine off open the temperature sensor slightly until air and coolant will flow...then close. The temp sensor is on the top rear of the block, drivers side. Start the engine and heat up to temp. The coolant bottle will look like a tea pot ready to explode but that's ok. You might need to do this a few times...let engine cool each time.

 

[RockyCodeHead]

My '87 has been boiling over badly since I bought it.

I picked it up in December. It's my first Jeep, but not my first truck. My last one was a '69 IH 1200D 4x4 with a 304 and T-18/NP-205... Enough about that one, I miss it a lot!

Anyhow, I went up and ran Switzerland Trail in Feb. Had about 4' of snow, packed well, air temp was about 34 deg. F. The truck boiled over twice driving up, though it was fine on the trail.

Since then I haven't been able to drive up the highway to Idaho Springs (about 18 miles) without overheating and just running the trail the truck overheats. (In fact I spent better than two hours in a hotel parking lot just last week after it boiled over and left me stuck. I spent the time dismantling the truck to try to determine the issue.)

I have flushed the cooling system, added water-wetter, hard wired the fan, replaced the thermostat, removed the A/C condensor and more. All seemingly to no avail. Then ... BAM! ... It hit me. I have been driving around with my Trans switched to "Power". Since I flipped it to "Comfort" it hasn't boiled over once!

I don't know what the switch does, but it sure seems to kill my cooling system!

Hope this helps in some way!

 

[5-90]

He's pulled the thermostat entirely, which obviates entrapped air (and, when he puts it back in, I've posted NUMEROUS times on drilling the thermostat - hint, hint...)

I had an auto instructor try to tell me that fan clutches are "lifetime" parts, but I've not personally known one to last more than five years in normal use, in the last 30 years or so. XJ's, since they run rather hotter and at lower speeds, would wear them out rather quicker - I change mine every three years, whether I need to or not (but I usually do.)

Anyhow, if you search for my posts on the subject, I tell you how to drill the thermostat flange to make the RENIX cooling system "self-purging" - which works, because I do it on all my rigs (all RENIX, by the by. All five of them...)

5-90

 

[Johnny V]

>pulled out the t-stat

Missed the one! Bummer!

Yep saw your post on drilling two holes in the thermostat last week...excellent!

>it will idle for about 20min or drive for about 5 at low speeds before it boils over out the overflow and blows the cap off of it

If you drive at highway speeds what happens? Does it overheat? If not then 5-90 is right on with a bad fan clutch.

If it over heats at highway speeds then the radiator is probably bad.

 

[5-90]

Knew I forgot something - according to the Jeep techs at the local, the OEM RENIX radiator is good for 150-180Kmiles. Replacement is indicated at that point.

They don't use OEMR either - most of the guys I talked to admitted to using my favourite - Modine. Damn things last forever if you flush them every alternate year...

5-90

 

[Johnny V]

> according to the Jeep techs at the local, the OEM RENIX radiator is good for 150-180Kmiles.

That's about right...mine didn't leak, it just stopped cooling after 160,000 miles. Replaced with a Modine.

 

[5-90]

> according to the Jeep techs at the local, the OEM RENIX radiator is good for 150-180Kmiles.

That's about right...mine didn't leak, it just stopped cooling after 160,000 miles. Replaced with a Modine.

Yep - that's what it does. I've been through it FOUR times!

5-90