Why is the jeep still overheating?

Question

I have a 1990 jeep cherokee and it is still overheating after i have replaced the water pump, radiator, and thermostat, the coolant also boils over and leaks out of the overflow tank, i know its not the radiator cap because the jeep doesnt come with one. ive done everything i can. i dont know whayt else to do so please help. thank you

Answer 1

I'm surprised your new radiator does not have a cap. Anyway, have you replaced the radiator fan switch? When the coolant temperature rises it tells the fan switch to kick on the cooling fan. Also, does you vehicle get hotter during idle or at stop lights? If so, it's your fan clutch. Good Luck.

Answer 2

Overhaeting can be caused by a variety of things. Since you've already replaced the radiator and thermostat, we can eliminate those items. The water pump won't usually matter unless it was badly rusted and corroded inside or if your belt is very loose and slipping.

A blown head gasket can cause overheating as you've described. To check for that you need to do a cooling system pressure check. Any qualified mechanic will have a cooling system pressure tester. It's applied to the radiator while cold in place of the radiator cap and pressured to around 15 PSI. After 30 minutes, the system should lose no pressure - if it does and there is no leak, then it's a bad head gasket. A bad head gasket will also usually result in small amounts of motor oil in the coolant which will float to the top.

Another elusive source for a leak can be the heater core. The coolant will produce a sweet smell inside the car and when the defroster is turned on full warm & you will notice fogging on the inside of the windshield.

The first easiest thing to check is the radiator cap. Jeep Cherokees do have them. It should be located on a tube placed in-line with the upper radiator hose near the battery. Click the second link below for a picture of one... A cap is pretty cheap and easy to replace, it's also an essential part of the cooling system as it will open at a specific pressure, allowing coolant to flow into your reservoir tank and later allow coolant to flow back into the radiator once the engine cools down. Cap springs get old, fatigue and fail to hold sufficient pressure to prevent boiling all the time. I would check that first.

Airflow through the radiator is also critical. Your Jeep's radiator should be completely free of bugs, leaves and other debris that could block airflow. Your fan shroud should be in place for maximum efficiency and your cooling fan should come on when the engine gets warm or when the A/C is switched on. Electric fans fail all the time and when they go, your engine will overheat when the vehicle is stopped.

If all of these things check out, you may also have rust and scale blockage inside the engine. If at some point your coolant appeared rusty, this is a possibility. Prestone and others make a cooling system flush solution which will help disolve this and may help.

Last and more remotely are that there is an engine problem causing the overheating. This can be bad ignition timing, lean fuel mixture, plugged catalytic converter, low oil level, or other mechanical problem. I would explore these options last if the Jeep is otherwise running well.

Good luck and I hope you get it resolved soon.

Answer 3

You should tell people if the Jeep overheats all the time or just at idle. On the highway at 50 mph is it still overheating? If so that would mean that you don't need to focus on the electric auxiliary fan. But... did you do the fan clutch (someone else mentioned) when you changed the water pump? Many people with the older XJ's switched to an aftermarket Electric fan and got rid of that stupid clutch/fan setup. I would recommend that if you plan on keeping it a few more years. Pay a shop $75 to get a compression check done on your engine and a pressure test of the cooling system.

Answer 4

It could be a bad head gasket.Check you oil for any traces of a milky white substance on the dipstick or in the oil itself.If it;s there the head gasket is blown and the cylinder head has to come off to replace it.If there is no milky traces then it's time to have the entire cooling system "power flushed" as you may have a blockage somewhere in the cooling system and only "power flushing" with it's chemicals can remove it.

Answer 5

If you opt to change the head gasket, first take a look at the water paths in the head. If they look plugged, then some idiot has used a stop/leak. Second, since you have the head off, route it to a machine shop. Chances are pretty good that it is cracked and/or warped.

Answer 6

i have the same jeep in the same year and had the same problem. i came out of autozone and coolant was allover the place.the right place to be. bought new coolant and went home and put on a new clutch fan its been good for about 1800 miles.. hope this helps have a good new years

Answer 7

think about a radiator or heater middle it truly is often plugged. once you've the a/c on, you'll run a larger temp. also, if the fan grab is going undesirable it received't spin quick sufficient to ideal cool the engine. you may want to also favor to envision the grill and note if the radiator is complete of grass clippings, insects, etc (i.e.) which will block the airflow by the radiator.

Answer 8

Well you may want to make sure none of the water hoses are callapsing and preventing water flow. And start checking out sensors. You may have had one go bad. Is your fan turning on? Is your thermastat opening. Take it out and throw it in a pan of boiling water and see if it opens. Then take it out and see if it closes. Hope you figure it out.

Answer 9

Sounds like cylinder compression is in your cooling system.Do a compression check & I'll bet'cha find low cyl. psi.Has it over heated enuff to damage a head or if yer lucky, just the head gasket ?

Answer 10

Check for a blockage also if your timing is too close to TDC.