Engine operating temps explained

[honesT]

Here is some well explained info I got from a Jeep forum, sorry I forgot who posted it or what site it`s from...

Please use a stock 195*F temperature so as your computer wont think it is still in the warm up cycle and stay in open loop meaning the O2 sensor is not read and you run rich. Also, the higher the temp you can get the more efficient your engine is. Engineers are running the temperatures higher as materials and designs improve.

For every 10F under 180F your engine wear rate doubles due to chemical reactions on the surface of the cylinder walls.

Running a 160F thermostat QUADRUPLES your engine wear rate. For every mile you drive your engine wears like it has been driven four miles. The chemical reactions drop little abrasive oxide particles in the oil that eats up the bearings and everything else as well.

The question of coolant temperature indirectly relates to cylinder temperature. But the issue from the engineering point is to have correct clearance for the piston and the piston rings.

If the cylinders do not warm properly, the piston never expands to it's intended shape...it may rock in the bore...which accellerates wear..The rings never expand fully...the result is blowdown into the crankcase. The combustion byproducts that get past contaminate the oil..the contaminants are spread throughout the engine...resulting in acid, moisture and particulate contamination.

Lastly, an engine is driven by heat...the less heat that goes out of the cooling system, the more is available for it's intended purpose....provide cylinder pressure...that is one if the reasons a warmer engine can be more efficient.


The other problem with a colder engine is that the oil may not burn off the water. Oil collects some water when it cools down. Running a lower temp thermostat or none at all can be done during the summer months or in the deep south. Still, I wouldn't do it myself. I did see an oil pan from a SBC in Tulsa that was just about filled with oil that was gelled. It was at an Auto Parts store. THe guy said the whole engine was that way. I would figure that he wasn't getting his oil heated up.

[honesT]

I forgot to mention my rad is leaking & I`m sticking to the stock rad, water pump & thermostate housing as many complications come with tinkering... Besides I live in beautiful canada so no desert crossings for me.

The thermostat with the most stable openings & closings and longer life is from what I have gathered the Stant superstat # 45359. The stant web site you can read all about it they go on to say that it has a high flow so I`m going to double check with them and post the response I get...

[steph74]

never heard about that particular thermostat.... curious to see about the outcome. Thanks for gathering the ionfo and reporting back ;)

[ike]

The pcm will go into closed loop @ about 140* if the o2 sensors are warm enough, which they usually are after about 2 min. This is a fact and can be verified by anyone that knows how to use a good scanner.

@ 160* the pcm doesn’t think it needs to be in warm up mode. This is a fact and can be verified by anyone that knows how to use a good scanner.

I would have to see real proof that @ 185-195* that the pistons and rings haven’t expanded enough for proper sealing vs 210*

Coolant temperature is directly related to cylinder temperature and efficient combustion.

If an engine is only run for lets say 15 min @ 210* it will have more moisture than if it is run for 1hr @ 185-195*.
Temperature is a factor, but how long the engine runs @ a given temperature is a more determining factor of moisture removal.

Many things can lead to an oil pan like that.
Not changing the oil often enough. Every 3000 miles may not be often enough if the vehicle doesn’t see many miles, or is not run enough to evaporate the moisture.
In a case like that one must follow the 4 times a year rule.
As in every 3000 miles or 3 months whichever comes first.
That vehicle that the little old lady only drives once a week to church and back…well it may not of had the oil changed in years.
The type of oil is also a factor.

In short you can run yours @ 210*+ if you want, I’m gonna get mine to run in the 185-195*range.

I think that is the range most xj owners are looking for also.

[jeepxj95]

yep i do. mine runs 195-200. if it runs 210 it starts to clime.

[honesT]

yep i do. mine runs 195-200. if it runs 210 it starts to clime.

Check your lower rad hose if you don`t have a spring inside the hose maybe see if the wreckers have an oem hose you can pull the spring out of and stuff in your aftermarket hose. I checked the Dealer but up here in Vancouver Canada they wanted $80+ Canadian dollars :crazy:, I tried 3 shops with no luck, no springs anymore. I`m going to give Jeep Thrills a ring tomorrow to see if my luck changes if not I`ll just use the spring from my old hose that has 224,000 km on it. Apparently from what I`ve read the spring should be in great shape to reuse if the fluid was changed before it went to crap.

[jeepxj95]

i checked when i put in my zj clutch fan last week. and it was there.

[gary63]

The pcm will go into closed loop @ about 140* if the o2 sensors are warm enough, which they usually are after about 2 min. This is a fact and can be verified by anyone that knows how to use a good scanner.

@ 160* the pcm doesn’t think it needs to be in warm up mode. This is a fact and can be verified by anyone that knows how to use a good scanner.

I would have to see real proof that @ 185-195* that the pistons and rings haven’t expanded enough for proper sealing vs 210*

Coolant temperature is directly related to cylinder temperature and efficient combustion.

If an engine is only run for lets say 15 min @ 210* it will have more moisture than if it is run for 1hr @ 185-195*.
Temperature is a factor, but how long the engine runs @ a given temperature is a more determining factor of moisture removal.

Many things can lead to an oil pan like that.
Not changing the oil often enough. Every 3000 miles may not be often enough if the vehicle doesn’t see many miles, or is not run enough to evaporate the moisture.
In a case like that one must follow the 4 times a year rule.
As in every 3000 miles or 3 months whichever comes first.
That vehicle that the little old lady only drives once a week to church and back…well it may not of had the oil changed in years.
The type of oil is also a factor.

In short you can run yours @ 210*+ if you want, I’m gonna get mine to run in the 185-195*range.

I think that is the range most xj owners are looking for also.

will I think you are right with the oil and you may be right about the temps.
but what I know around here for sevrole jx owners we have found if you go
below 195 on your temp. your gas mileage goes down. So around here we shoot for 195-210.

[xj4life2]

In all honesty (no pun intended) your both right on the temp issue, depending on the year of the jeep and what the computer actually controls , Newer vehicles require the hotter temps while the older do not. However I have found the even with my older 90 jeep I run the factory temp t stat and factory water pump and t stat outlet and have had very few issues at all. Granted she does run warmer in the hotter temps but never above 210* which is the factory desired running temp for the 4.0 motor.And as sugested put a scanner on the rig start it and actually find out at what temp it goes to comp control and base your decisions from there. Most shops will be happy to do it for ya for a minimal charge, but this info is very strategic when it comes to cooling system mods!!! Lastly let me add that basic system maintenance and regular oil changes are a must especially on the 4.0 motor, lastly check or replace your o2 sensor every tune up, its the trigger for the computer if its not working you'll never achieve computer control.

[Carves]

The pcm will go into closed loop @ about 140* if the o2 sensors are warm enough, which they usually are after about 2 min. This is a fact and can be verified by anyone that knows how to use a good scanner.

@ 160* the pcm doesn’t think it needs to be in warm up mode. This is a fact and can be verified by anyone that knows how to use a good scanner.

I would have to see real proof that @ 185-195* that the pistons and rings haven’t expanded enough for proper sealing vs 210*

Coolant temperature is directly related to cylinder temperature and efficient combustion.

If an engine is only run for lets say 15 min @ 210* it will have more moisture than if it is run for 1hr @ 185-195*.
Temperature is a factor, but how long the engine runs @ a given temperature is a more determining factor of moisture removal.

Many things can lead to an oil pan like that.
Not changing the oil often enough. Every 3000 miles may not be often enough if the vehicle doesn’t see many miles, or is not run enough to evaporate the moisture.
In a case like that one must follow the 4 times a year rule.
As in every 3000 miles or 3 months whichever comes first.
That vehicle that the little old lady only drives once a week to church and back…well it may not of had the oil changed in years.
The type of oil is also a factor.

In short you can run yours @ 210*+ if you want, I’m gonna get mine to run in the 185-195*range.

I think that is the range most xj owners are looking for also.


:thumbsup:

OBDII .. Goes Closed Loop within a coupla minutes as mentioned .... and coincidentally by about the time the coolant temp has got to about 65*. OBDI should be similiar ... since both use heated O2 sensors for the same reason i.e. getting into Closed Loop ASAP.


As near as I can figure ... and based on the PCM having a number of preset fuel parameter settings - that it uses depending on all the sensor inputs .... Closed Loop just optimises each of those as they are used.

What is the ideal running temp is open to conjecture .... and the driving circumstances.

I prefer about 190*/195* .... but 210* would be fine if the temp gauge didnt go epilectic - at the slightest heavy duty tasking coz the cooling system stuggles - to maintain high and stable running temps.

[honesT]

Check your lower rad hose if you don`t have a spring inside the hose maybe see if the wreckers have an oem hose you can pull the spring out of and stuff in your aftermarket hose. I checked the Dealer but up here in Vancouver Canada they wanted $80+ Canadian dollars :crazy:, I tried 3 shops with no luck, no springs anymore. I`m going to give Jeep Thrills a ring tomorrow to see if my luck changes if not I`ll just use the spring from my old hose that has 224,000 km on it. Apparently from what I`ve read the spring should be in great shape to reuse if the fluid was changed before it went to crap.


Just to update on my findings, the newer style rad hoses are thicker and stronger than the oldies, with that said I found the Goodyear brand to have the most rigidity. Costs a few more bucks but well worth it for piece of mind. It takes some calling around but you`ll find a vendor sooner or later I found mine at the second shop I walked into...

[honesT]

Also I have another Jeep from my last one that was a right off due to a texting asshole who had booze on his breath:mad:

Just installed the Stant superstat # 45359 and it looks like it is getting up to operating temp faster than the stock Chrysler jobber...

It`s also stated by others that it keeps the temp closer to the stated range than the others so a lot less fluctuation. Cost is a few more bucks I think mine here in Canada was $12.

Cheers

[Carves]

Also I have another Jeep from my last one that was a right off due to a texting asshole who had booze on his breath:mad:


That sucks .. :mad:



....... Just installed the Stant superstat # 45359 and it looks like it is getting up to operating temp faster than the stock Chrysler jobber...

It`s also stated by others that it keeps the temp closer to the stated range than the others so a lot less fluctuation. Cost is a few more bucks I think mine here in Canada was $12.

Cheers


Have seen a few posts where the Stant has not, always been the bees knees.

Generally tho - they appear to be as good as the MotoRad ones ... with only a few, having issues out of the box.


Despite my having read damn near every XJ cooling system article on the planet ... I havent yet found a, stated operating range.

Lotsa internet beliefs ... and various examples of individuals, vehicle op temps, ... but the factory manuals just state that a 195*f t'stat is fitted as stock,

.... unless of course ... the buyer requested the factory option 180*f t'stat.


Depending on the operating area climate, and which of three factory radiators are fitted, and how the vehicle is driven ... there will be various "operating temps".

FWIW ... as long as about 200* is the, constant average temp, displayed on a quality temp gauge,
... and the radiator /clutchfan, are good enough so that the electric fan isnt constantly operating - due to high coolant temps ... Be Happy .. ;);) .. :D


Mine runs at 195* all year round ... give or take a few degrees, from summer to winter,

... its happy ... and so am I .. :D

[honesT]

I could be wrong but I think I remember reading somewhere the Jeeps with the tow package came with or gave the option of the 180 thermostat.

This would make sense for towing but what about those times when your not..

If it was true you could get a 180 ordered from the factory than any 4.0 should be happy with the 180 regardless of towing or not...

[bruggz351]

Gday. I run a 180* thermostat.

XJ stays on 180* all day every day all year round, as long as its only passengers.

Any towing, is a different story. Easy going, and it stays around 180*, But stick a hill in the way and the temp will very quickly rise to the 210* mark. It wont boil, I have the cooling system pretty well sorted. Only the E-fan is permanently on.

I also have a huge trans fluid cooler, and bypassed the oil cooler in the radiator completely.

cheers

[Carves]

Gday. I run a 180* thermostat.

XJ stays on 180* all day every day all year round, as long as its only passengers.

Any towing, is a different story. Easy going, and it stays around 180*, But stick a hill in the way and the temp will very quickly rise to the 210* mark. It wont boil, I have the cooling system pretty well sorted. Only the E-fan is permanently on.

I also have a huge trans fluid cooler, and bypassed the oil cooler in the radiator completely.

cheers


Next time you have it apart ... bang in a 190* or 192* for a trial,

Its what I use ... seems ideal with my AdRad and Tectyl 60plus, low eth-gly content coolant.

btw ... hows your hypnotised dog .. :D:D

[bruggz351]

Next time you have it apart ... bang in a 190* or 192* for a trial,

Its what I use ... seems ideal with my AdRad and Tectyl 60plus, low eth-gly content coolant.

btw ... hows your hypnotised dog .. :D:D
It'll be due for a going over, this or next month. So, yeah, I'll grab a 190. Worth a try I reckon, see if it stabilizes, somewhat.

Hahaha, me poor blue dog. Yeah, he's ok. Bit more burko than usual, but ok. :p:D

Funny thing actually, he found a dead rat, bloody big one. Wouldn't touch it, just sniff.:p anyhow, he takes a good wiff of this stinky rat, runs off, and has a big spew. Hahahahaha:D:D:D
Big tough blue dog.;)

[KMW-NWXJ]

My '91 runs straight up at the 200 mark all the time for normal driving. But I did notice on a trail crawling slow in low range in low 90s heat it climbed up to the tick mark just before the red zone. I kept a close eye on it and it didn't get any higher than that at all, but it stayed right there until I hit the open road again and got some air flow. Does this sound normal?

[Cheromaniac]

Despite my having read damn near every XJ cooling system article on the planet ... I havent yet found a stated operating range.

The 4.0 was intended to run between 195*F (the stock t'stat opening temp.) and 220*F (electric fan on temp.). In a temperate climate a 195*F t'stat is just what you need.
If you live in Arctic conditions you could run a 205*F t'stat to help the engine warm up faster.
If you live in a hot desert climate, you could run a 180*F t'stat to keep cylinder head temps. down and reduce the risk of pinging (especially if the fuel quality is poor). Even then you could carry a spare bottle of octane booster in the vehicle just in case.
If you live in an equatorial climate where the ambient temp is never below 75*F perennially, you could even run the engine without a t'stat 'cause the warm-up time would still be short.

The only aftermarket t'stats I've ever used were either Robertshaw or JET, and both are good with each having a lifespan of about 6 years.

I've been running a 180*F for 16 years and it has had NO negative impact on gas mileage, so don't believe some internet myths.

If you do a lot of towing you need a thicker radiator and a bigger auto trans. cooler to shed the extra heat. A lower temp. t'stat is NOT going to help you.


OBDII .. Goes Closed Loop within a coupla minutes as mentioned .... and coincidentally by about the time the coolant temp has got to about 65*C (150*F). OBDI should be similiar ... since both use heated O2 sensors for the same reason i.e. getting into Closed Loop ASAP.


That is correct, and OBD I is the same. Therefore gas mileage should be unaffected even if you run a 160*F t'stat but you do risk accelerated engine wear and sludging of the oil.

If your engine runs hot or overheats, running a lower temp. t'stat will NOT solve the problem unless it's a sticking t'stat that's causing it in the first place.

If your engine runs hot or overheats on the highway, the most likely reason is a blocked radiator core (or radiator too small). Winches or big driving lights mounted in front of the grille are other common reasons. Don't forget to check the drivebelt tension too.

If your engine runs hot or overheats at idle/crawling at slow speeds, the most likely reason is that your fan(s) isn't pulling enough air through the radiator. If you have a viscous clutch fan, make sure it's properly shrouded and check that the viscous clutch stiffens up when the engine's hot. If you have an electric fan, make sure that it switches on when the coolant temp. reaches 220*F (gauge at 5/8). If the electric fan only works when you use the AC/defrost, check the engine coolant temp. sensor in the t'stat housing.

[honesT]

My '91 runs straight up at the 200 mark all the time for normal driving. But I did notice on a trail crawling slow in low range in low 90s heat it climbed up to the tick mark just before the red zone. I kept a close eye on it and it didn't get any higher than that at all, but it stayed right there until I hit the open road again and got some air flow. Does this sound normal?

Sounds like your clutch fan is on the way out, time for a new one is my guess...

I had an AMC Eagle wagon that was running fine until I took it threw a deep water crossing pushing a swell of water above the front emblem :/

That cooked my clutch fan and when in slow traffic or long lights the temp would rise.

[KMW-NWXJ]

So its basically slipping and not spinning at its full speed?

[Carves]

So its basically slipping and not spinning at its full speed?


Thats the usual issue in the case of a failing fan.

You could try scrubbing clean the spring - on the front of the fan clutch ... if its covered in gunk,

but usually its the clutch action failing.

[Carves]

...... I've been running a 180*F for 16 years and it has had NO negative impact on gas mileage, so don't believe some internet myths ......


Yep ... the cylinder walls being awash with petrol because a genuine jeep 195* t'stat isnt fitted,

... is probably the faerie tale I most enjoy reading ... out of all of them .. ;);)


Thanks for the OBDI / OBDII comparo too .. :thumbsup:

... pre '97 info ... is a little lacking in the FSMs. ;)

[bruggz351]

Yep ... the cylinder walls being awash with petrol because a genuine jeep 195* t'stat isnt fitted,



That's rich... :rolleye0018::bacondance::smiley-scared003: