studmuffin

Hey guys well thanks in advance first of all.
Well i got some overheating issues, i thought i had fixed it because a valve broke, then my hose that comes out of the coolant resovoir started leaking, i also replaced the thermostat, but i noticed that my friends 95 xj has a radiator cap on top of his radiator but my 88 does not? so thats why im asking if that normal or is the another inlet where the water goes cuz i dont think the coolant in my resovoir is circulating, dont think its the pump since the band has not seized. anyone have a clue where this cap might be?

XJ Stryker

You have a Closed cooling system which is all that was available for a XJ in 88. You just fill it from the over pressure bottle.

PingPong

I am in the middle of doing the conversion from the closed system to the open one. So far no Issues, just a PITA figuring out how to mount the heater control valve from the donor vehicle.

studmuffin

oh ok, and where is that located, is it the resovoir located in the back where you put the coolant.

5-90

You'll find it at the rear of the engine bay, on the passenger side.

Typical longevity for those bottles is somewhere around ten years (on a good one,) you can source a new bottle and cap from Morris 4x4 Center without too much trouble. My advice is to get one now so you have it when you need it.

There's no "intrinsic flaw" in the closed system, just a few things to bear in mind:
1) Life of the pressure bottle, as stated previously.
2) Radiator service life (OEM) runs somewhere around 150-180Kmiles. Aftermarket replacements can run indefinitely, properly cared for. I tend to use Modine or Performance Radiator (I can get them locally for jobber,) but reports from the field on CSF radiators are also uniformly excellent - and Dirk at DPG Offroad sponsors an awful lot of boards like this, so Google him.
3) Air pockets can become trapped behind the thermostat. Easy enough - when you replace the thermostat, drill two 1/16" to 1/8" holes in the flange, 180* apart, and install with the holes at 12:00 and 6:00. The upper hole passes air from behind the thermostat, the lower hole passes coolant to displace the air - the system purges itself. Problem solved.

studmuffin

oh wow that third step is pretty good, ima look into that. so on the pressure bottle if there is leak on the hose from it? thats what is causing it to overheat since its not sealed. fixing that leak you think it will do the job?

what do you guys think bout running without a thermostat, so it will never overheat, lol good or bad

warrpath4x4

Check the FAQ for cooling.

What I did in my 87 is install a 92 thermostat housing, and where the sensor would go, you install a drain ****. Still drill the hole in the thermostat flange to release air. With this setup you can point the front of your jeep uphill and burp your system (might take a couple times). Other wise you will have to remove the sensor at the back of your intake to release the air. If you don't get the air out, it will overheat and blow a headgasket or worse.

Onto your question about removing the thermostat all together. You still run the chance of overheating even without one. The function of your thermostat is to restrict the flow of coolant that your water pump is pushing so it can flow at the right pace through your radiator. If your coolant is flowing too fast, its not cooling off in the radiator.

studmuffin

oh ok i get you, ithought it would be better without the thermostat cuz of the free flow, its jus it would take longer to get the hot air which i dont mind at all since its texas. but dont want that to happen with what you said. hmmmmmm? so what do you suggest for me to do, i jus dont thhink the coolant is circulating that its supposed too.

5-90

Coolant doesn't really change the boiling point of the water - it does depress the freezing point, and it gives useful additives (surfactants, lubricants, anti-foam, ...)

Water boils at 212*F. The XJ likes to run about 210*F. For each 1psig of pressure on the water, the boiling point is increased by 3*F - and the RENIX cap is rated for something like 13psig. 13x3 = 39, 212 + 39 = 251. Therefore, steam should not begin to form pockets until 251*F - if everything is in proper working order.

A leak means the system won't hold pressure anymore - and you're running an operating temperature right under the boiling point, so you're going to get steam pockets forming in rather short order. PROBLEM!

As far as the "no thermostat" goes, the main idea behind the thermostat is to allow the engine to reach operating temperature, and to act as a flow restrictor to keep coolant from going through the radiator too fast - which gives time for it to reject heat into the atmosphere. If you run without a thermostat, you may not actually get up to operating temperature, which typically ends up harming fuel economy at the very least.

In thirty years, I have seen precisely three vehicles that benefitted from not having a thermostat installed, and they would actually overheat if one was in place - even after a full cooling system clean and refit! They were:
1980 Honda Accord, 1800c/c CVCC engine.
1985 Chevvy Cavalier, 173ci V6-60 engine.
1988 Jeep Cherokee, 242ci I6 engine.

I have yet to figure out why they were that way. I personally owned all three of these vehicles, and it was me personally that did the cooling system flush and refit - I just can't figure it out. I still have the XJ - it's a damned fine truck, it just doesn't like having a thermostat. I have no idea why, but every time I tried to install one, it would overheat within fifteen minutes. I tried installing a restrictor plate instead, and it overheated inside of thirty minutes. I leave the thermostat housing empty, and it runs at a rock solid 190*F (which is more in line with where I want to run anyhow, and hasn't caused any trouble - with either fuel economy or exhaust emissions,) so I honestly don't know what to say. I, for one, am fully baffled.

studmuffin

haha well buddy mine is a 1988 cherokee 242 inline, haha, so you think mine might jus work without it, cuz i wanna drive mine already so im probably jus gonna take it off, worked for you so it must work for me since its the exact same model and motor right?

5-90

Not necessarily - I've had five RENIX XJ's with the 242ci I6, and the 88 is the only one that didn't like having the thermostat. One of the 1990's I had had already been converted to the later "open" cooling system, and it ran the warmest of the five (I was seriously considering converting it back.)

I knew of three Cavaliers with the V6 engine, that were within 5,000 of the sequential part of my VIN, but they all ran just fine normally. I was the odd one.

I still don't know what caused it, but it was real, it was odd, and it was definitely one-off. Don't assume that just because you've got the same year/model/engine that it's your problem - this is rare enough to border on being unique.

I got your PM, and already answered that as well.