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Temp question?

V

voudoux

NAXJA Forum User
Location
Piedmont NC
Why does the late model xj run so high of an engine temp?is it pollution related or something else? Any ideas,as I can't think of any good reasons for it. Thanks
 
Define high? 210-ish is normal.
 
Right 210 is normal for the xj and probably most modern cars , but why? They make 160/180 thermostats for older cars, so why does late model stuff run so "high" in relation to older? Why run so close to the edge? Just a question, Thanks for the reply.
 
Car technology changes. Engine operating temperatures that seemed ideal a generation ago no longer are. Emissions requirements are always getting tighter. Consumers are demanding better fuel economy. I think a lot of people are misguided in thinking cooler is better, when what they should focus on is whether it's within the specification set down by the builder. I've seen some cars not turn on their cooling fan until they hit 225F. Perfectly normal, according to that car's specs. Just my .02, anyway.

--Chris
 
voudoux said:
Right 210 is normal for the xj and probably most modern cars, but why? They make 160/180 thermostats for older cars, so why does late model stuff run so "high" in relation to older? Why run so close to the edge? Just a question, Thanks for the reply.
Click to expand...


New synthetic oils and tranny fluid can handle the higher temperatures. Fuel economy is improved at the high temperatures. Electronic thermostat controlled e-fans allow then to run it closer to the edge. Most 96 and newer vehicles I have worked on run between 210 and 222 F, and the E-fan does not even run till 220 F and turns off at 210 F.
 
Thanks Chris,so it is an emissions issue that sounds about right as the mileage on my 2 xjs couldn't have actually been improved.( it's a joke). 210 does not leave much of a cusihion. I wonder what they reenginered in this engine to make it work better at these temps the Ramblers with the 232s sure didn't run that hot? And neither did my 258 cj5. I don't believe all I am told by these experts,I have been told by dealership mechanics that the only thing Chrysler changed on the 3.8 in my wrangler to run the light weight oil was the oil filler cap. But if you don't know something first hand it is just hearsay.Sorry got off subject,Thanks for the reply.
 
voudoux said:
Thanks Chris,so it is an emissions issue that sounds about right as the mileage on my 2 xjs couldn't have actually been improved.( it's a joke). 210 does not leave much of a cusihion. I wonder what they reenginered in this engine to make it work better at these temps the Ramblers with the 232s sure didn't run that hot? And neither did my 258 cj5. I don't believe all I am told by these experts,I have been told by dealership mechanics that the only thing Chrysler changed on the 3.8 in my wrangler to run the light weight oil was the oil filler cap. But if you don't know something first hand it is just hearsay.Sorry got off subject,Thanks for the reply.
Click to expand...

It is an emissions issue yes, from the standpoint of improving MPGs (and thus reducing emissions per mile) since OBD-II started in 1996. At the higher temps the intake manifold is hotter and the engine combustion chamber is hotter helping to better vaporize the fuel better so it burns more completely. They also raised the Fuel pressure to avoid vapor lock.

I tried running mine on lower T-stats and the mileage dropped.
 
Thanks Ecomike for the reply I understand what you are saying,and it is about what I thought. It was just a question that came to mind yesterday while I was stuck inside waiting for TS Hermine to go away.
 
And a 195 thermostat only means it begins to open at 195. It's not fully open until 210 or something like that. Also the viscosity rating of motor oil is measured at 210. As in 10w30 I believe it's 10 at 32 degrees and 30 at 210 degrees.
 
voudoux said:
Why does the late model xj run so high of an engine temp?is it pollution related or something else? Any ideas,as I can't think of any good reasons for it. Thanks
Click to expand...

Government demands the lowest emissions possible; higher engine temperature helps achieve this. Sheep go along with this nonsense.

I run a 180-degree thermostat and a 3-row, all-copper radiator in my 2001 XJ. Everything else is stock. Coolant entering the engine is 153 degrees, and coolant exiting the engine is exactly 181 degrees, measured with an IR gun, a/c on or off.

I get 25 mpg hwy, 19 city, day in, day out. It runs like new, even with 185k on the clock. Closed loop operation happens at 140 degrees. No emissions-related CEL's have ever happened. The hood is merely warm to the touch, even on a 115-degree day. It has always passed the most probative smog check imaginable, even in CA.

I see no reason to BBQ my XJ to make government smog fanatics happy. Molon labe.
 
This sounds encouraging,I was wondering at what temp the computer went to normal running. I nun a 190 in my 1999 4.0 xj. Never had any problems , gas mileage did not change. I may try it and see, I also run a fail to open thermostat( if it fails it goes to the open position) have not heard much about them on this forum. Any ideas on the 4 cyl engines,does the 140 degree figure stay the some,it is a 1998. Thanks great info!!!
 
Emissions, wear, power, etc. If you want some really fun reading, see if you can find the Continental Motors 60-hours engine test data. Long story short, years ago (I think it was the '30's!) they ran three identical engines at different temperatures for 60 hours straight and found that the engine which was being run at 195+ degrees made more power, achieved better fuel economy, and showed less engine wear. Higher engine temps also make it harder for steam that's produced by burning fuel in the engine from condensing back into water and running into the oil or wherever you don't want water to be. Overheating an engine's bad for sure, but running an engine too cold will kill it just as sure as overheating it will.
 
JeepNoob said:
Emissions, wear, power, etc. If you want some really fun reading, see if you can find the Continental Motors 60-hours engine test data. Long story short, years ago (I think it was the '30's!) they ran three identical engines at different temperatures for 60 hours straight and found that the engine which was being run at 195+ degrees made more power, achieved better fuel economy, and showed less engine wear. Higher engine temps also make it harder for steam that's produced by burning fuel in the engine from condensing back into water and running into the oil or wherever you don't want water to be. Overheating an engine's bad for sure, but running an engine too cold will kill it just as sure as overheating it will.
Click to expand...


And yet I ran several vehicles with 180 F T-stats in Houston for decades, one for over 400,000 miles with no problems. I disagree with the comments about water and engine wear, especially a 60 hour engine wear test. Was that new engine? Huge difference between a used engine going for 400,000 miles and 60 hour test stand test on what was likely a new engine.Not even sure how they could measure engine wear in just hours.

That said, if there was a difference in engine wear it was because there was less gasoline in the oil at 195 F than at 185 F, especially with a carburator. Not because of a slight difference in water in the oil in my opinion. At the higher temps the gasoline vaporizes more completely, burns more completely, thus it gives better MPGs, more power and also dilutes the oil less because it burns more completely. They also may have had fewer miss fires in that particular engine at 195 F than at 180 F making the conclusions questionable (too little data, used just one engine).

Also on the old cars, you got a lot more low end power on a cold engine start up, because the air was colder and denser!!!!
 
180 degrees is about the cut-off point. Check it out-

97314d1386886667-engine-temps-vs-wear-cylwallwearvstemp_640x480.jpg

With a 160 T-stat though, you're running right pretty much right at that 180 degree mark, even with the thermostat wide open...
 
Take some time to read about Smokey Yunick's hot vapor engines and his thoughts on engine temperature. The short answer to your question is the higher temps are a trade off by engineers for: emissions, fuel economy, engine packaging, assembly process, longevity and finally cost. We as the end consumers can determine which of those often competing issues are most important to us. I prefer a cooler running engine in normal operation so that I have a larger safety margin in severe duty situations.
 
Sorry to take so long to reply,I agree, l am working on my 2.5 4cyl xj now it would be a good time to try a different thermostat (160/180).But I have not ffound out at what temp the 4cyl goes to normal ( I think the term is closed loop) running. I am in the process of installing a instrument cluster with actual gauges,not just lights,what genus engineer came up with a dash for a Jeep with no heat,oil ,or battery gauges? I could go on for quite awhile on this topic, but Not now. Thanks
 
voudoux said:
Right 210 is normal for the xj and probably most modern cars , but why? They make 160/180 thermostats for older cars, so why does late model stuff run so "high" in relation to older? Why run so close to the edge? Just a question, Thanks for the reply.
Click to expand...

It really isn't close to the edge. With the additional pressure from the radiator cap, it raises the boiling point of water significantly. IIRC, it goes to around 250 at sea level.
 
I wonder exactly what company that was? My 1966 Jeep Gladiator came with a 326ci Continental motor! It also had a "flat" oil pan rail!
 
I understand, but why run so hot if you don't have to? Heat is detrimental to the life of many engine parts that are not metal so why push it if you don't have to,what is the advantage of it.l have read many of your replays and value your opinion. Thanks
 
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