Thadeous

Greetings,

Recently purchased an 88' XJ. 4.0 Liter, 6 cyl with two fancy doors on it. This is my first jeep ever, and I fell in love with it the minute I saw it, even though it didn't run at the time (had been abandoned for almost 4 years). Myself and some friends have put a new Transmission in and I have spent hours working on the electrical.

So, on to the question. When I first got the Jeep in running condition, I would notice that the thermostat would shoot up to just shy of the red zone then drop back down to around 210. . .climb back up, then shoot back down. This cycle would repeat endlessly unless I was on the highway at speeds of around 70mph. Keep in mind climbing, dropping, elevation changes or temperature variance seems not to affect this either on the highway or not.

This being the case I replaced the thermostat (195 degree). Same symptoms. After reading these forums for a bit and reading the advice here--that seemed to indicate the closed system on the older Cherokee's suck--I replaced the existing radiator with brand new stock radiator for a 91' Cherokee.

Now the Jeep will heat up to nearly the start of the red zone after being started, then it will drop down to around 217-222, and stay there. No more cycling. However, the temperature seems warm to me as temperatures seem to be running around 60 to 70 degrees here at the time being.

The main fan is working, and it also has an accessory fan wired to the ignition (so it is basically always on). During the install of the new radiator the fan shroud shattered, so will have to get that replaced if any of you folks think that may be effecting the system.

Do any of the wise Jeep Yoda's have any thoughts on what I should do? My fan seems to be functioning fine, so I wouldn't think I am having issues with the clutch....

Hmmm.

Thanks.

VTJeep

Don't know much about Renix.. You sure dummy gauge is working properly? Might be worth double checking with temp gun.. Burp system?

Thadeous

I could attempt to burp the system. However, from what I have read, the cycling would be more pronounced in that situation--similar to what I was suffering BEFORE the radiator was changed.

You may be very well correct that the dummy gauge is not functioning properly. I may have to hit it with a gun and see. I appreciate the advice. If that checks out I wonder what my next step should be? Clutch Fan/Water Pump I would guess. . .

What would be the best place to hit for a solid temperature read?

Keep in mind I am new at this.

Pelican

I'm not sure what you read but you can never go wrong burping either the closed or open system and both systems absolutely must be without air pockets to function properly. A properly functioning open system ('91+) will self-burp over several heat/cool cycles provided that it is filled carefully to start with.

I assume you changed out the whole closed system to an open system when you installed the '91 radiator.

The shroud is important but I don't know if that will cause your symptoms.

highmileage

The hard fluctuations could be crud still in the system I might flush it a few more times. The temp should be @210ish some run cooler some a little hotter, but getting over 220 es no bueno. A bad head gasket or a cracked head can cause the same thing to happen,by letting hot exhaust gasses into the cooling system.

Thadeous

The last car I had with a bad head gasket caused a lot more heat than this thing is experiencing, it was not occasional, and never leveled off like this one does. Also, the coolant was fouled, which this coolant is not. Though should all else fail I will have to check on that.

@Pelican: I basically put in the new radiator, and linked the two hoses that led to the plastic tank (thus removing the tank). The cooling sytem seemed to only require 3/4 to 80% of a container of coolant. (4 quarts of a 5 quart jug).

@highmileage: Wouldn't I also be having some other nasty symptoms with a cracked head/gasket issue?

How should I go about burping the system?

Thadeous

Here is a stupid noob question I need to ask.

The mid point on temp gauge reads 210. The Max Point reads 260. So, I assume that means the third mark should be roughly 235 degrees? My assumption that the car is reading between 215 and 222 is based on the idea that having the needle rest about a third of the way between the 210 mark and the third mark (which I assume is roughly 235 degrees) on the heat gauge indicates it is running about that temp.

Radi

I think your math is correct. Halfway between 210 and 260 is 235. Get an infrared thermometer before you get too deep into it, you may be chasing a non-problem.

PNWjeeper

Point the infrared thermometer at the thermostat housing. The missing shroud could vary well be the weak link in the system. Dealership wants about $60+, junkyards (around here) wanted $50, best place I found was partsgeek for about $18 shipped. Let's see what else... Ah probably the best way to burp the system is to use the temp gauges hole. There is a link in my signature about renix sensor diagnosis it has the location of the temp sensor in it. Point the nose down (since air rises) its located at the back of the head on the drivers side (again link in signature has a picture)
I think that's all for now. Good luck.

Thadeous

Mini update of a sort:

Have not had the chance to get an IR thermometer at the thermostat housing at this point. However, due to the suggestion that I might be having head/head gasket issues I did some on the spot tests recommended to check for that.

I have no bubbles on the dipstick.
I am not bubbling through the radiator. (Or I should say that with the cap off I notice no distinctive bubbling. . .I do not have an overflow tank on the radiator either and it seems to never be boiling over--even when the temp supposedly reaches in the 230's)
I took a paper towel to my exhaust. Car does not currently have a cat or a muffler, and while fluid was being ejected by tailpipe (warming up on a cold morning) the fluid was clear in color and did not stain a paper towel.

Just wanted to get those basic checks out of the way just in case.

djb383

Mathematically, here's how the gauge breaks down and 241.25F starts the red zone. LOL

Thadeous

Used an IR gun to hit the thermostat housing, right where the hoses comes in. The highest reading I could get on the thing, while the gun was almost touching the housing was roughly 218. Meanwhile my thermostat was reading a happy 230 to 235 in the dash. I am not boiling over ever, so this can't be right. I would just chalk it up to a bad temp gauge, but the thing that keeps haunting me is the cycling up and down. . .especially right after the car starts.


Per our friends gauge, which breaks down about as I had assumed, then I am hitting roughly 240 after start up. It cools down to about 215 climbs back up, drops, climb back up, drops, then after a while seems to stabilize at around 220?

PNWjeeper

That could all be related to the faulty sensor, there's no way to be certain until its replaced that I know of. It is accurate...ish if when the gauge finally settles its the same temp as what you had on the IR gun. On rock auto a new sensor runs between $7-$65 averaging in the teens though.

djb383

Good coolant, properly mixed, with a correct and properly functioning rad cap won't boil 'til about 260F.

prerunner1982

With no overflow tank there is no where for it to boil over too. I would put the over flow tank back in the system. There should be a "nipple" up around the radiator cap that should have a small line leading to the over flow tank. When the heat rises and the pressure builds the rad cap will open allowing the coolant to escape into the over flow. The system will also pull coolant from the tank back into the system.

My gauge will sometimes do the show hot for a second and then settle back down trick, but it will settle at around 200*.

Also figuring the thermostat housing may be dissipating some of the heat the temp gauge may not be that far off.