Ok so I have an overheating problem that I can't seem to figure out.

First a little info on the jeep in question. 89 cherokee limited, 4.0, 240k
I have replaced the fan clutch, waterpump, thermostat, and headgasket.

Now for the problem, it get up to operating temp (200 - 210) within 10 min, then it will cool back down (assuming when the thermostat opens, then back to 210. At a stop it will heatup but once I start driving again it will cool right back down, driving at an idle it will heatup. Everytime I incress the rpms the temp will drop back to a good operating temp.

I am currently looking at replacing the radiator. I want to upgrade to a 2 or 3 row and would like some input on brands. I do not plan on changing the system setup, but maybe open to it, if it makes the system more stable.

I have another 89 cheokee, 4.0 that I will also be working on as it is starting to show signs of heating problems also.

Both are dailly drivers on the central coast of california, niether see much offroad time. But cannot says for sure what the po's have done.

 

I bought one of these:
http://www.championradiators.com/
for a different vehicle. All aluminum three-row, the workmanship is excellent. Very happy with it. I'm sure it's Chinese made, but they're on their game with these.

What brand thermostat did you use? Some are known to have issues in the 4.0.

 

Replace the radiator. Excellent time to update to the open system. If not, use 83501426AC stat from dealer and 703-1396 cap from Napa.

 

think the stat was a duralast from autozone.... i know but it was the only thing I could get at the time.

As far as the upgrade to the open system what parts would I need. Still toying with the idea of the open system as the plastic bottle in the closed system just seems like a design problem

 

If the temp goes up than back down after a bit, your thermostat is working.
upgrading radiator is a good idea.

The closed loop system is a little problematic but when it works, it works great as there is more water circulating in the engine.
The problem with it is air in the system. the only way to fill it up properly, is to disconnect the upper radiator hose and fill from there then re connect and top up the bottle to the top of the little plastic piece inside, warm up engine and re-fill as necessary. After your first drive that was long enough to bring it up to running temperature, check the level again.

go play

 

You can buy a radiator with a filler neck on it that also has a place for your fan switch. I don't know the number off hand. Then fit an averflow bottle.

The REnix cooling system works well when it works. The issue now is that the bottles that are available are absolute crap, as are the caps that come with them. I still use this system on 3 of my Jeeps, but with the 703-1396 cap. That cap is more secure on the threads, even of a chinese bottle. The bottles only seem to last a year or two before they crack. Lifetime warranty but I don't like that crap.

 

Explanation regarding "more water circulating in the engine" please.

 

Simple. in newer systems with an oveflow thank, the fluid inside the tank does not "circulate". All its for is a place for the water to go when it warms up and expands. the only fluid actually used for cooling is whats in the rad, the engine and the heater core and also the lines.

the old type, the tank is part of the circuit, when the fluid expands, even the expanded fluids is still being used for cooling. therefore, you can say that about 1 more liter/quart of fluid is part of the actualing cooling at all time.
This system is succesfully used on many many marine applications. in my oppinion, it is better. just a real pain in the but to fill properly to make it work properly.

 

Don't flame me guys, but I have NEVER burped/bled or anything a Renix Jeep since we got them in new at the dealership in 1987.

 

I interpreted the statement as there is more coolant inside the engine block/head (.......the motor).

Not sure what u mean by "newer systems".....closed vs open are just 2 different bottle types....1 bottle is pressurized, closed to the atmosphere and the other bottle is not pressurized and open to the atmosphere. Yes, earlier XJs used a closed system and later XJs used a open system but neither cools better than the other and both types of coolant bottles are being used, even today in all kinds of different vehicles. Coolant circulates (flows in/out of both bottle types), in a little different fashion of course, but nothing to effect/improve cooling performance of one system vs the other. Both are coolant expansion/recovery bottles.....one pressurized, one not.

 

U mean to tell me that the Renix service manual didn't have cooling system "burping" instructions in big bold type saying elevate the rear of the vehicle higher than the front AND remove the temp gauge sending unit in the back of the head before filling the cooling system? Really? LOL

 

It may. But I've never done it, nor did my techs at the dealership from 87 til 92.

Actually, under refilling instructions in the 1990 engine manual, there is NO MENTION of doing any more than filling the bottle to the top of the post that's inside.

 

Check this out from the FSM

This system does not have a radiator pressure cap. Instead the pressure cap is mounted on the coolant pressure bottle. System coolant flows directly through a fully pressurized Hot-Type expansion bottle. Coolant flows through the pressure bottle at all times during engine operation whether the engine is cold or at normal operating temperatures.

Larger coolant volume caused by thermal expansion during engine operation is absorbed by the expansion chamber in the bottle. Air trapped in the system is purged through the pressure cap vent valve during maximum coolant expansion..

 

Well I'll be switched.......guess the Renix FSM needs to be re-written in order to coincide with the jack-up the rear/remove the sending unit burp method.(facetious)

 

Suppose so. Why let facts get in the way of conjecture and old wives' tales?