So i ran my 99 Cherokee hot a couple of weeks ago. Had it towed home and flushed the radiator and put in a new thermostat. The radiator looked horrible though so I made note to change it asap. Saturday all of a sudden the heat gauge pegs out. I limp halfway home stopping to let it cool and get towed the rest of the way. Today i put in a new radiator, thermostat, serp belt, and upper and lower radiator hoses. I also put some of that blue devil stuff in in case I had any damage from the overheating. During the 50 minute idle with the blue devil and no thermostat in, it ran fine but as soon as I put the new thermostat in, it went right back to how it was acting Saturday. Runs fine for a few minutes then the heat shoots up. By the way...When it was overheating saturday before all of this work, it blew the anti freeze everywhere out of the resevoir tank. So... could it be my water pump? My oil is clear. Any input would be greatly appreciated.
Ned

 

I'll bet its the water pump. Getting ready to replace mine in my 99 also.

 

Rocky Road-
Wonder why it ran fine without the thermostat. Would that hide the fact that the water pump is bad?

 

Usually when water pumps start going, they leak first at the little bushing weep hole at the bottom.
when it leaks there it means the coolant is making it pass the bushing that should not be letting water out.

NOW: Rule of thumb. if it decides to overheat for no apparent reason. CHANGE THE THERMOSTAT.
If it blows a hose change the hose. if it gets hot again, CHANGE THE THERMOSTAT.
Don't go for the low temp ones. they hurt your engine.
go for the factory temperature recommendation. 195°F (90°C).
When filling up the engine, take your time. it holds approx 12qt of liquid. A lot of time 1 gal will fit and air will stop the rest from going in.

I hope that helps...

 

I don't think it's your water pump. What brand of stat did you use? So many are junk nowdays. It's also possible the new stat was airlocked.

I'm not familiar with Blue Devil (heard of it, but have no experience with it).

 

Missed the part about removing the thermostat. Did you drive around, get up to operating temp with the stat out? Get another thermostat and try, but if you are replacing the entire cooling system anyway, why leave a suspect pump in the mix? Preventive maintenance.
Pump sounds weak to me.

 

It was recommended to me to change the water pump when I changed the radiator. I had about 78k on it. I bought it with 64k and found that the head had been replaced. They did a shotty job of flushing the radiator. I changed it and the thermostat and it runs like new. Get the premade gasket AND use hi temp RTV. ALSO, don't get the cheap thermostat from Autozone, I learned that the head way.

 

I think its a bad thermostat or in upside down.

 

Start here

 

also, i went through all of this and it eneded up needing a fan clutch as well. i just went ahead and changed everything. thermostat, temp sensor, radiator, hoses, water pump, and fan clutch. eneded up costing me about $300 total, but well worth it since it satys just below 210 now.

 

What is Blue Devil? Don't put any crap in your cooling system that it wasn't designed for.

 

Thanks everyone. I'm gonna mess with it some more today and probably change the water pump. The thermostat is brand new and the spring side is in toward the engine. Could something be fouling the thermostat. I replaced it two weeks ago and again yesterday.

 

I'm pretty sure it's going to be your water pump. they are really easy to change and they aren't expensive. also, after you pull the water pump, flush your cooling system to get all of that blue devil crap out of there.

 

That does not mean it is good!

You can test it though.

In a pot of water, turn up the heat and see that it is opening and closing ..... measure water temp if possible.

If it does not open up, or it only opens up when the water begins to boil it is NO GOOD.

 

The only additive I put in my coolant is called Purple Ice and it's made by Royal Purple. It's kinda like Water Wetter in a way.