Running hot - Resolved

[81cherokee laredo]

I've been working on getting the cherokee back on the road. The latest problem I'm runing into is she's getting up to the high end of the green band on the coolant guage. I've driven to work a couple of times with her, symptoms are: Doesn't get hot in morning, about middle of green band. In the afternoon, when it warms up is when i have the problems, usually about 10-15min into the drive home. When it gets to the point where im really worried about over heating, I'll pull over and put her in park, pop the hood and let it idle. About 10-15min of idling brings the temp back down to the middle of green band. So my thoughts were old coolant might be causing problem, maybe pump was failing to circulate enough at highway speed. So I drained fluid, changed out the pump, thermostat(170 degree) all new hoses added new 50/50 pre mixed fluid. Problem still remains, if not getting hotter quicker (probably due to lower temp on T-stat). My next step is to change the fan clutch and radiater cap,(I know a little bass ackward) should have changed first, but coolant was pretty nasty. The question is, am i missing anything here, have i overlooked any thing? should i get rid of the clutch fan?

[Billygoat]

I bet the fan clutch is shot - get a good thermal one

[Mark Wilde]

Yep, get a new, good quality fan clutch. Other than that, green is still...well, green. These things seem to vary on indicated temperature from rig to rig so much that it's impossible to compare one to the other. I had an 85, bone stock, that in summer it would sit happily in the middle of the guage. I would tell you, as long as you're not approaching the red, you are not overheating.

The 401 I put into my 90, on the other hand...is a complete thread on overheating by itself...

[travisrda]

you sould also get a manual oil and temp guage that way you know exactly what you are dealing with (those stock guages are quite often wrong) do you have a fan shroud? that might help a bit if you don't already have one.

[81cherokee laredo]

Thanks for the inputs guys, sounds like im going to go ahead and get a new thermal clutch for the fan and try that next. I trust my guages for the most part, she is getting hot and creeping to close to the red for my liking. whats this mystical fan shroud thingy, I havent had a problem without one in the past.

[Woodchomper]

A fan shroud would definitely help your cooling problems. Also, do a search for Hayden 2797 if you want to put in heavy duty clutch fan.

[81cherokee laredo]

I agree a fan shroud would definatly help out, but finding one is quite a challenge. I've owned the cherokee for over a decade and have never had a shroud on it, it never got above the half way point on the guage in the past. Thanks for the tip on the HD clutch

[joe]

How long as it been lifted? Running hot start after the lift? Fan shrouds are good at speed. The turbulence created by the front axle really disturbs the air behind the radiator and eng bay. The shroud is there so the fan pulls air directly from the front and through the radiator, with no shroud the fan will pull air from the sides w/o pulling it through the rad. The turbulence created by the axle gets worse on a lifted rig. On a stock rig those little rubber air dams you see under the front isn't there to help keep the front end planted at 100 mph it's there to help reduce turbulence. the higher it off the pavement the less functional it is. On a 30 year old rig with a poor maint history( w/o frequent coolant flush/changes) you prolly have other cooling issues too(rad, clutch, pump etc) but a shroud is a good thing to put back on if you run on the freeway.

[Tornado230]

Have the radiator checked for flow at a good shop.
It might be time for a new one.

[81cherokee laredo]

You bring up alot of good ponts Joe, I would run a shroud if i had one, and the problem didn't start till after the lift and tires. Tornado230 thats going to be my next step if the clutch doesnt fix problem

[Blacksmith01]

At highway speeds the fan shouldn't have to pull anything through the rad. If it works good enough to cool it down while in park or slow driving then you have something else going on.

[joe]

At highway speeds the fan shouldn't have to pull anything through the rad. If it works good enough to cool it down while in park or slow driving then you have something else going on.

You'd think so but it's just the opposite in reality. the more RPM's the hotter the motor runs and airflow "through" the rad is more important. Standing still in calm air idling the fan pulls easily from the front drawing enough air through the rad. Not so at speed. With turbulence in the eng bay the fan pulls from the easiest source.(the sides). Your theory works for air scoops, open windows etc but the radiator is a serious restriction to airflow. Just cause air is hitting it at a greater velocity doesn't mean it's passing "through" the radiator. It's the fans job to pull it through. The greater engine heat of running at higher RPMs isn't compensated for by the air hitting the radiator harder or faster. If that were true you wouldn't need a radiator with cooling coils or a fan just a metal tank bolted to the front of the car. It needs more air "through" the radiator. Ok not a great explanation but best I can do. I'm done, it's your engine y'all do what'cha want.

[svining]

You've already replaced your Water pump...But

If you look around you can find a High performance Water Pump, for about the same money as a conventional pump. I had read a few threads on cooling issues and when I needed a pump I got one from Advanced Aut....with discounts it was the same as a conventional pump.

Like I said its too late now after you replaced the pump...as nobody is made of money.

You'd think so but it's just the opposite in reality. the more RPM's the hotter the motor runs and airflow "through" the rad is more important. Standing still in calm air idling the fan pulls easily from the front drawing enough air through the rad. Not so at speed. With turbulence in the eng bay the fan pulls from the easiest source.(the sides). Your theory works for air scoops, open windows etc but the radiator is a serious restriction to airflow. Just cause air is hitting it at a greater velocity doesn't mean it's passing "through" the radiator. It's the fans job to pull it through. The greater engine heat of running at higher RPMs isn't compensated for by the air hitting the radiator harder or faster. If that were true you wouldn't need a radiator with cooling coils or a fan just a metal tank bolted to the front of the car. It needs more air "through" the radiator. Ok not a great explanation but best I can do. I'm done, it's your engine y'all do what'cha want.

[jpcoutts]

I agree with Joe, the extra turbulence created by the lift have a big impact on air flow. Additionally, everything in your system has aged and become a little less efficient over time. This is particularly true if the coolant hasn't been changed regularly. Shrouds can be found, try posting in the "wanted" section if you can't find one elsewhere. Somebody may even post here with one for you.

[FSJunkie]

Lower radiator hose could be collapseing with from the suction of the water pump if the cap isn't holding high enough pressure.

• Replace your radiator cap
• Rev the engine up in the driveway and watch for a collapseing hose.
• Fan clutch, thermal type with the spring in front.
• Fan shroud