Optimal operating temperature revisited.

The first three months I owned my 88, I spent a lot of time on the cooling system. I kept the closed system intact, and replaced almost all of it with new parts. My goal was to keep temps below 210 at all times! I actually wanted to run at 200* at all times if I could pull it off. I upgraded to a heavy duty fan clutch, but I did leave the 195* T-stat in place. (I was tempted to swap in a 180 but decided against it) Well, I DID succeed at keeping everything below 210 for the summer, and now that it is getting cold outside (35 degrees today here in Jersey) I have gotten my wish to run a constant 200*. Here's the rub... Now my heater is so inefficient I will be at the parts counter soon to pick up a higher temp T-stat for the winter. Moral of the story is be careful what you wish for! LOL I may try blocking part of the rad first. Anyone else do that to get better heat? Does it work? I don't think 200 degrees is perfect any more, I think 210 is the magic number as long as you can hold it from going OVER 210. (at least in the closed systems where anything over 210 makes your bottle crack prematurely.)

i would try blocking the radiator also, maybe remove mechanical fan??

With the 4.0, you should have plenty of heat in the cab at anywhere in the 200-210 range. I doubt that a different stat will make much of a difference. You may have other inefficiencies in your cooling system that is preventing good heat from making it into the cab. Specifically the heater core is most suspect, especially in your vintage XJ. Have you flushed it and or replaced it? Along with the heater control valve, a clean heater core is essential to keeping the tootsies warm in the winter.

I only had one vehicle that I was forced to use cardboard on. It was a Jeep Scrambler soft-top 4 cylinder. Not a great vehicle choice for Minnesota where the temps can reach thirty below!! Was like driving a tent down the interstate. That 4 cylinder just would not warm up despite all of my efforts. I think of cardboard as a "last resort".

• Is yours equipped with a heater control valve? 91 to 96 have a little plastic POS, but my 90 had a sort of heater control valve made of metal. I believe that had a vac line to actuate it as I just plugged mine in to the new part when I converted to open. If so that could be weak, failing or just doesn't have enough vac to it.
• Have you completely flushed the heater core, independently of the cooling system as a whole? Just straight garden hose water in the upper and lower ports, alternating til it runs clear. It can get gunky in there even though you've flushed the system (smaller tubing).
• Are all the blend doors operating and is your vac system tight?

My heater ran quite warm even when I errantly put in a 180 t-stat, I can't tell any difference from then to now (I have an OEM 195 t-stat in there now). My thinking would not even include the t-stat.

P.S. Don't remove any fans.

I had the radiator, the block and the heater core flushed less than a year ago when I got it, and every single hose including the y connectors and heater valve are new. Not saying the heater does not work, but it takes a LONG time to reach temp, and it is far from toasty! It IS possible the heater core should be replaced, I will grant that.

ParadiseXJ said:

My heater ran quite warm even when I errantly put in a 180 t-stat, I can't tell any difference from then to now (I have an OEM 195 t-stat in there now). My thinking would not even include the t-stat.

P.S. Don't remove any fans.

Click to expand...

LOL... Not gonna remove any fans, But I did have a "bad" t-stat that was stuck open in a different truck that completely KILLED my heat. So the T-stat is in play. I may do another flush of the heater core when I get a nicer day to be sure it is not gunked up.

EDIT: I sincerely think it should be running at a higher temp than it is running at now... <shrug>

I have my entire rad blocked(this year, last year ran 5 small holes and was still cold) with a piece of tin. Did it today at lunch actually. 31" x 9" piece of tin, sprayed it black and zip-tied. I used to lose my heat in the morning on the highway, not anymore

Through all the madness of changing hoses, is it possible your heater core lines are not where they should be?

Get rid of the HD fan clutch? I bet that is robbing some power too compared to a stock clutch.

Thanks for all the replies and ideas... I like the HD fan clutch in the 99 degree summer heat, but it's not all that hard to swap in and out... and flushing the heater core is another great idea that I will do on a warm day this fall. I want to get a slightly higher ratio of antifreeze in it for the winter, and that will get the temps up a little bit too as water runs cooler than antifreeze... If it REALLY gets cold out, I can always cut and spray a piece of tin too. Great Ideas, thanks! And all easier than swapping T-stats twice a year! Did I say thanks for all the input...

knock on wood* i have a hard time getting my jeep above 200 when im driving even in the summer, then in traffic or wheeling she runs right around 210, for some reason ive had good luck with the stock cooling system plus a 195 tstat

redneckboarder said:

knock on wood* i have a hard time getting my jeep above 200 when im driving even in the summer, then in traffic or wheeling she runs right around 210, for some reason ive had good luck with the stock cooling system plus a 195 tstat

Click to expand...

That's exactly what I was aiming for, and it worked out nicely for me, but I need my heat! LOL Take care of your cooling system, and it will stay cool for you! You're lucky you got one without gremlins in the cooling system! (I know they're hiding in your XJ somewhere! They love XJs!) LOL

most of them live in the u joints and rear end, i keep askin for gremlin free ones at napa but i guess they dont check too thoroughly

xj88superjeep said:

I want to get a slightly higher ratio of antifreeze in it for the winter, and that will get the temps up a little bit too as water runs cooler than antifreeze...

Click to expand...

You want approximately a 50-50 mixture of antifreeze to water (preferably deionized water). If you're at that level, you're good to approximately 30 below farenheit, I can't remember the exact number. You want to shoot for this ratio but keep in mind that variations on this are going to have NO effect whatsoever on the engine temperature or the heat you are getting.

200 degrees is enough engine temp to provide proper heat. My recommendation is to concentrate your efforts not so much on engine temperature as components involved with providing that engine temp to the cab. Heater core is DEFINITELY the first place to look. It is probably the most common cause of problems, especially in your vintage XJ.

birchlakeXJ said:

You want approximately a 50-50 mixture of antifreeze to water (preferably deionized water). If you're at that level, you're good to approximately 30 below farenheit, I can't remember the exact number. You want to shoot for this ratio but keep in mind that variations on this are going to have NO effect whatsoever on the engine temperature or the heat you are getting.

Click to expand...

This is not entirely true.... but thanks for the input....




[SIZE=+1]Physical Properties of Liquids[/SIZE]
Liquids have a few properties that need to be understood before we can proceed. Chemistry isn't everyone's favorite subject, so well keep it as simple as possible:

• [SIZE=-1]Specific heat. Specific heat is the amount of heat that it takes to raise the temperature of a standard amount of fluid a standard degree of temperature. For example, one BTU is the amount of heat needed to raise one pound of water one degree F. To raise the temperature of a pound of water ten degrees, we need ten BTUs. This is true any place between the freezing point and boiling point of water. A fluid with a higher specific heat has greater capacity to absorb heat, which is a desirable property for a coolant. Here are the specific heats of the three principal coolants:[/SIZE]

[SIZE=-1]Substance[/SIZE]______________ [SIZE=-1]Specific Heat[/SIZE]
[SIZE=-1]Ethylene Glycol[/SIZE]_____________ [SIZE=-1].57[/SIZE] [SIZE=-1]
Propylene Glycol[/SIZE] [SIZE=-1]____________.59[/SIZE] [SIZE=-1]
Water____________________[/SIZE]_[SIZE=-1]1.00[/SIZE]

the HD fan clutch runs all the time, I have to remove mine for the winter too

ehall said:

the HD fan clutch runs all the time, I have to remove mine for the winter too

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Good, I'm not the only one.... LOL

A quick side note... I've found in my searches that for those of us with closed cooling systems. If you raise the ratio of antifreeze to water, to maybe 70/30, you will lower the cooling system pressure, and relieve some of the stress on your pressure bottle.