What causes vehicles to run hot?

[daveleau]

Hi everybody!

I have an 87 Jeep XJ (Cherokee) and it is running hot. It just started 3-4 days ago and it gets hot driving the 2.5 miles to work. I know of one issue where there is a plastic bottle that acts as the reservoir for the coolant. This is under pressure and can crack. When it leaks, the engine runs hot b/c the coolant is not under pressure and will not circulate. Other than this, what could cause a vehicle to run hot?

The gauge never went above 100C until last week and it was very stable temp-wise.

Thanks
Dave

[SPEEDO]

Water Pump or Thermostat would be my guess.

[Knothead]

Hi, Dave, I think you're right, you'll need to get that bottle handled.

Speedo's suggestions are good, try wiggling the fan...does it wiggle? Water pump. (Of course, if it's THAT bad, you'll likely see a puddle underneath. Sooooo....)

Where you're at, climate-wise, you really don't need a thermostat. Out here, we rarely get temps below 50, so we just take them puppies out and make weapons out of 'em.

[pickel]

Knot.. You ALWAYS need a thermostat !!! Coolant will go through the system too quickly and not get the system to operating temperature. I use a 160 in the summer and a 185 in the winter in my Big Block and a 195 in the imports for the computer control. Dave check the fan clutch and water pump first. the reservior bottle isn't under pressure, only when use turn off the motor and temp builds up and open the rad. cap to releive the pressure in the engine. When it cools down the mixture is sucked back into the engine til full.( if there enough liquid in the bottle) Probably need a flush and fill and a new thermostat. I'd do that first. Get a backflow kit from an auto parts store and some Zerox quick flush , some new antifreeze and follow the directions.

[Gomer]

Let it get up to temperature... if the upper hose is not hot I'd suspect the thermostat.

Explain the issue with the overflow for me a little better. Pickel has explained its function well, but I don't understand the problem you are having with it.

[daveleau]

Hi guys. Thanks for the help thusfar.

The fan is rock solid. No wiggling. There is no puddle of water. Would this rule out the water pump?

The system seemed to be running hot on Thursday, but when I revved the engine, the temp needle went down to normal. If I let it idle, it'd get hot. Yesterday, I had other things on my mind on my way home and I forgot to monitor it. By the time I got home, the Jeep didn't smell too good and it was bubbling and girgling.

[daveleau]

As for the bottle, the guy I bought the Jeep from said he'd had temp problems before but getting the new bottle fixed it. He said the Jeep 4.0L engine had a strange cooling system and that bottle is under pressure. When it is cracked, it won't cool correctly.

I can't find any reference to this in my Haynes manual or my Chiltons CD.

[pickel]

Sounds like a blown head gasket !!!!! Been there , done that a few times. Check to see if there is water in theoil or steam coimng out of the exhaust pipe...
Do you have to add coolant regularly ?????

[daveleau]

No steam coming out of the exhaust. How would I check to see if there's water in the oil?

I haven't had to add coolant since I got it a whole 6 weeks ago. I've taken it on one long (4 hour) trip and the rest has been on short trips.

[Chuckiechan]

Sounds like a clogged radiator.

Call a shop and see if it can be cleaned and repaired (rodded out). If so, do that.

Water in the oil? Pull the dipstick and if you see a brown creme floating on or mixed in the oil, you likely have a blown head gasket. Pull the spark plugs and look for heavy deposits on them. Clean or replace them.

Thermostat, yes you need it. Take it out and boil it and see if it opens at about 180 degrees. Or just replace it. $5.00 ?

If the coolant tank is cracked, go to U-Pull it and replace it. It is supposed to hold coolant overflow that gets sucked back in.