need some help with running hot

[Mudderoy]

IR Temp gauge is aces! $85 for a Fluke off of Amazon.

 

[Ecomike]

if it only happens on the freeway it is probably your clutch fan, google how to test cause i dont remember it is either supposed to be hard to spin when hot or easy. you should be able to find the info i think it is even in the chiltons. and i got 20 bucks that says thats your problem.

I'll take that $20. He already said he has a new HD ZJ (Grand Cherokee) clutch on it. And you have it backwards, a dead clutch makes you overheat at idle, not at highway speeds.

 

[Ecomike]

Harbour Freight has 2 IR testers that run from $10 to $30 on sale.

Don't go over 50% antifreeze, you want at least 50% DI water in the mix.

Have you replaced the radiator cap? Or tried an 18 lb cap yet?

There are better radiators out there. I am upgrading my 2 row, 4 year old aluminum to a 3 row all copper/brass CSF radiator for the same problem you are having.

Is this a renix, colsed cooling system, or a newer open cooling system?

Have you checked the head on that new 98-99? engine to see if it has the notorius 0330 head that is known for cracking? If not I would look into that possibilty next. There is a casting number on the head, passenger side IIRC. If it is the 0330 (IRRC it was the 0330 heads), count on it being cracked, and that being your problem.

I take it you have the E fan running off the 98-99 PCM controls which turns the fan on at 210-220 F at the T-stat housing, based on the T-state temperature sensor reading that the PCM monitors, where as Renix used a thermal switch in the radiator to turn it on at 180 F at the radiator coolant return side. Is this correct?

I have heard of exhaust leaks blowing on the tranny, overheating the tranny fluid, which overheated the radiator coolant. I would check for exhaust leaks anywhere near the engine & Tranny.

I would be curious to know if yours over heats in park, at 2500 rpm? versus highways runs at 2500 rpm? (that eliminates the transmission from the equation, but also adds the fan clutch versus highway wind cooling).

You need to check your AC high pressure side, and make sure you don't have too much refrigerant, thus elevating your AC pressure, condenser temps and engine load. While your ac may be adding to the problem, it is not the entire problem at this point.

You need to get a "block tester" kit, rental (free rent, just pay a deposit and buy the fluid, about $7 for the fluid) to check the coolant for exhaust gases. Autozone, Advanced Auto and O'Reileys have them in there tool rental areas. They also have a rentable radiator pressure tester and cap tester tool kit that is invaluable for isolating this sort of problem.

Get a cheap, IR temp gauge, and follow Winterbeater and Muderoys lead on testing the thermostat sensor and dash gauge to make sure you have an overheating problem, and not a gauge sensor problem. Consider a full time on toggle switch for the e-fan to buy you some buffer.

Is the AC system all Renix hardware with R-12, All R-134a hardware from the newer donor, 98-99 vintage, or is it an R-12 condenser attached to a newer R-134a compressor set up? If it is R-12 condenser with the rest R-134a, then that is adding to the problem and you may need to upgrade the AC condenser (something I doing this week) to 97-98 parallel flow condenser. But find and fix the other problem first.

 

[winterbeater]

Minor revision: The notorious "0331" head. Look for milky residue on oil filler cap. I get the other head numbers scrambled, but not the one on my 2000.

 

[ehall]

did you put the thermostat facing the right way? spring side goes in the engine

 

[Ecomike]

Minor revision: The notorious "0331" head. Look for milky residue on oil filler cap. I get the other head numbers scrambled, but not the one on my 2000.

Thanks for the correction. I was thinking it was 2000, but close enough since he was not sure of the year when he posted 98-99?

ehall, from the sound of it, he did. If the thermostat was in backwards, his problems would be much worse, IMHO.

I forgot to mention getting an anolog multi meter and testing the O2 sensor output to see what those numbers show. If it is running lean, or rich?

Also the IR gauge can be used to check the exhaust for poor flow, hot spots at the Cat converter.

 

[chrslefty]

The head is a 0630 ,I'm still running all renix electronics ,sensor in the rad and two on the t-stat housing .
It is a open cooling system .
The ac compressor is a conversion ,orignal to the jeep as far as I know .
Ill have to try the high rpms n the drive way test .
I don't have a ir gun ,that ll be on the list of things to get .
T-stat is deffinatly in the right way .
Ill cheack the voltage on the 02 sensor .
Thanks for all of your help so far.

 

[Ecomike]

The head is a 0630 ,I'm still running all renix electronics ,sensor in the rad and two on the t-stat housing .
It is a open cooling system .
The ac compressor is a conversion ,orignal to the jeep as far as I know .
Ill have to try the high rpms n the drive way test .
I don't have a ir gun ,that ll be on the list of things to get .
T-stat is deffinatly in the right way .
Ill cheack the voltage on the 02 sensor .
Thanks for all of your help so far.

So what is turning on your Efan? A stock Renix control system should turn it on at 185 F at the radiator outlet (if it is all Renix), which is about 210-215 F at the T-stat housing on a properly working system.

Mine turns on at 185 F and off at 165 F, temps read at the radiator outlet side with an IR gauge. That correlates to about 210 on and 195 off at the T-stat housing, or about a 30 F increase as the coolant travels through the engine.

 

[old_man]

Make sure the system is burped correctly. The easiest method is to unscrew the temp sender on the back of the head slightly, until fluid comes out.

An inaccurate temp sender/gauge would be my second bet.

I have my rig wired so that I can manually override the E fan and it helps, even on the highway.

If you aren't blowing coolant, I wouldn't get too worried. If it really was running hot, you would be venting out the overflow.

Running lean can cause high speed over heat. If you have done a spark plug reading and they weren't white you probably aren't running lean, but for a last check to make sure things are fine, I would take the vehicle to a mechanic that has a dyno with a tail pipe sniffer. Have him run the speed up and put it under a load while checking your mixture.

 

[chrslefty]

Ill post up some pics in a few so u can see exactly what I have going on that might help.
I can not burp the system using the sensor port in the back of the head beacouse its blocked of . Which is the reason that the sensor is now in the t-stat housing , I did drill holes in the t-stat to help with that tho.
I went with the rad that I have specificaly for the reason that it has the switch housing in the stock location ,same as a renix ,but also had a filler neack to alow me to have a open conversion .
So I might look at getting a aftermarket gauge to make sure I'm getting acurait readings .the coolant has never actual boiled over of came out of the over flow tank .
It was my understanding that the switch came on at 220 and off at 210 for the renix . Gess I was way off on that .

 

[themud]

just out of curoisity try really sweating it out and turn on the heat and see if the temps drop on both the freeway and idling... If the temps drop on the free way that means your radiator is plugged a bit.. the other thing is completely drain the whole thing and fill it with 3/4 gallon of antifreeze no more and the rest with distilled water and see if that helps... I have a 95 and the sensor on the tstat cover controls the fans and the one on the back of the head is you temp guage on the dash you might just have a problem combining the new with the old stuff.. your best bet is to get an IR gun and do some random testing mine said it was hot and the gun showed that it never got over 215 at any time and that was sitting and idling with the hood open and the a/c on during the summer... I would also check your cat at when I trashed mine it severly overheated just trying to get on the freeway...

 

[jdougn]

My '98 4.0 was overheating at highway speeds but not at idle or lower speeds. We found the cat to be partially blocked.
dn

 

[Ecomike]

Ill post up some pics in a few so u can see exactly what I have going on that might help.
I can not burp the system using the sensor port in the back of the head beacouse its blocked of . Which is the reason that the sensor is now in the t-stat housing , I did drill holes in the t-stat to help with that tho.
I went with the rad that I have specificaly for the reason that it has the switch housing in the stock location ,same as a renix ,but also had a filler neack to alow me to have a open conversion .
So I might look at getting a aftermarket gauge to make sure I'm getting acurait readings .the coolant has never actual boiled over of came out of the over flow tank .
It was my understanding that the switch came on at 220 and off at 210 for the renix . Gess I was way off on that .

The Renix switch has about 20 to 23 F on/off differential (at least mine does, and did when new). Keep in mind the stock location was the cold side of the radiator, and there is a good 30 to 35 F differential from the cold side of the radiator to the hottest part of the engine coolant, at the T-Stat housing. So a switch temp depends on location.

The 220 on, 210 off range is typical of the HO engines, where the computer runs the Efan based of T-Stat temp sensor readings. I don't like running that high on a DD. I like to run 180 to 200 peak.

 

[Jeep450r]

turn off the A/C

 

[chrslefty]

ha ha!! Says the guy from northern Cali . sure bud why don't u come down here and ride around with me and id be more than happy to .

OK picture time .
so this is what i have going on maybe it will help .please excuse the rats nest . i still need to shorten some wires and replace some loom .
here's the sensor on the rad its kinda hard to see . Ur looking down from the drivers side by the air box .

this is the t-stat housing .it has the block and gage sensors .

pass side. you can see the the hoses for the heater core . it goes straight trough.

drivers side overview .

the new tranny cooler .

im gonna get a aftermarket gage hopefully tomarrow and see what that says .
and yes i like zipties ,and i know i need a new hose i have 1 just need the $ to get the system recharged .

 

[scragglepoo]

Just curious how is the serpentine belt tension?
faster you go the more you slip...

 

[chrslefty]

i went with the twist method on that 1 . i don't have the $ for the tool to check tension .
i guess ill give a little up date tho.
so i went for a drive .and of course it started to get hot ,like a hair from the red. so i turned off the ac .and once it cooled down to just past the 210 mark and traffic was moving i turned the ac back on and it got to about the 3/4 mark .and stayed there tell i had gotten were i was going .
well when i was ready to leave i was checking all of the fluid levels and i noticed that the bubble the was on my low pressure line (ac) was no longer in existence . so i drove home sans a/c . didn't over heat didn't budge past the 210 mark. well it was a cool night so i figured that was making it easier on the cooling system .
yesterday was on the freeway 100 + outside temps and kinda humid for phx .was driving along the freeway at 65-70mph unfortunately no a/c and the temp never got past the 210 mark .
so I'm looking for a new compressor .i all ready have a new hose and ill see what happens after that .
no i don't have the temp gage yet . I'm thinking that the stock one cant be off by that much and i don't understand how to do the test with the resistor's .
is there a link for a newer style a/c compressor ?

 

[ehall]

It's really important to have confidence in your gauge, but not too good to have false confidence. The way I calibrated was to get a buddy with a scanner to read my computer temp, while I swapped in replacement sensors and senders until I could get the computer and gauge to agree. I ended up reusing a Standard sensor that was about 5 degrees warmer than my old stock unit, but went through two Standard senders and an old stock sender, until I finally found a cheapo Autozone Duralast/Wells sender that was almost exactly the same as the sensor. Now I know that when the gauge shows 190 cruising down the highway and 220 at a long red light in the summer, it is telling me the truth.

One other thing with the sender in the tstat housing is that the temperature fluctuations can be really extreme as the tstat opens and closes. The tstat isn't an on-off switch, but instead opens and closes as temperature rises and falls and might not fully open until over 210. Sometimes you see this with temp creep up to 220, rapidly fall to 180 as the tstat reaches fully open position, and then start slowly rising again.

 

[chrslefty]

unfortunaly i cant read the temp from te puter .its a renix .i dont see extream temp flux unless i just came off the freeway and im sitting at a light ,and the aux fan kicks in and cools it down .

 

[Ecomike]

It's really important to have confidence in your gauge, but not too good to have false confidence. The way I calibrated was to get a buddy with a scanner to read my computer temp, while I swapped in replacement sensors and senders until I could get the computer and gauge to agree. I ended up reusing a Standard sensor that was about 5 degrees warmer than my old stock unit, but went through two Standard senders and an old stock sender, until I finally found a cheapo Autozone Duralast/Wells sender that was almost exactly the same as the sensor. Now I know that when the gauge shows 190 cruising down the highway and 220 at a long red light in the summer, it is telling me the truth.

One other thing with the sender in the tstat housing is that the temperature fluctuations can be really extreme as the tstat opens and closes. The tstat isn't an on-off switch, but instead opens and closes as temperature rises and falls and might not fully open until over 210. Sometimes you see this with temp creep up to 220, rapidly fall to 180 as the tstat reaches fully open position, and then start slowly rising again.

Regarding that cheapo AZ temp sender, I hate to point out that all that work was based on the assumption the the T-sensor in the T-stat housing is delivering accurate temp data. Otherwise they are both lying to you, just telling you the same lies!:roflmao:

I have no doubt you already know that, just having fun, and pointing it out for future would be enthusiasts here.

On the temp drop when that thermostat opens, for other readers, the temp drop is due to a temperature gradient in the cooling system from the T-stat back to the radiator outlet, which can be a good 45 F drop in a matter of 10-20 seconds as the flow is restored.