Thermostat question

With the onset of summer, I've noticed that my 2001 XJ is climbing over the 210degF mark on the temperature gauge. This happens in motion, in traffic, on trails, A/C on or off. It doesn't get hot enough that it's going into the red or that the electric fan can't bring it back down, but it is crawling up to around the 220-225degF mark - just enough to make me antsy.

This has me a bit concerned as I'll be heading out to Las Vegas later this month, as well as doing some running around out in the desert while I'm there. The plan is to change out the coolant before I leave (just did the tranny last weekend, which has helped a bit), but I'm thinking of going to a 180degF thermostat at the same time.

My question is this: though the engine should run a bit cooler, will the engine management richen the mixture to raise the temperature? My concern is that there's no point dropping in the cooler thermostat if I'm just going to end up hurting fuel economy (and risking a smog test failure) while receiving no real additional cooling benefit.

Oh, and those LeBaron vents look like a good idea, too. I'm adding that to the to-do list for cheap & easy mods.

Since your 4.0 doesn't have any performance mods, I suggest that you keep to a 195* rated t'stat. Replace your old one with a Robertshaw 195* unit from http://www.flowkooler.com/thermos.php?FKSID=be2c4357b67efa7e173abf044228dbc2 with part no. 330-195
If you're gonna install hood vents, place them as close to the front of the hood as possible where there's negative air pressure above the hood when driving at speed. If you place them at the back, the air pressure above the hood is positive and you'll have air going into the engine bay instead of coming out.

What he said. Also you can check out the manual fan over ride switch from XJ-Armor. I set that up this weekend along with some spacers for the hood to raise it by an inch. Just enough to tilt the hood forward and let hot air out.
www.xj-armor.com
look under electrinics. Juice

Thanks, folks, much appreciated. I'll definitely be checking out the manual fan switch; it sounds like a decent backup approach to the issue. Out of curiosity, what would the downsides be to running a 180degF thermostat over the 195?

I just did my thermostat last night for Prev-Maint. It was the original and I found it was cocked almost 90 Deg. from vertical(small hole in 'stat should be UP). Mine (2000 Sport) ran a tad past the middle of 210 on the gage. It's right where it should be now! I got my t-stat at a dealer due to bad luck with
aftermarket. It's cheap insurance.

waxworm53

casm said:

Thanks, folks, much appreciated. I'll definitely be checking out the manual fan switch; it sounds like a decent backup approach to the issue. Out of curiosity, what would the downsides be to running a 180degF thermostat over the 195?

Click to expand...

180 isn't cold enough to fool the computer into staying in open loop mode, but it won't help you. Once a thermostat is open, it's open. If your 195 degree thermostat is functional, it's wide open at 210 degrees. Once you get above that it means the cooling system isn't doing the job and it has nothing to do with the thermostat.

Remember, the purpose of a thermostat is to keep the temperature UP, not down. Trying to "cure" an overheating problem with a colder (or no) thermostat is an exercise in futility.

I've been running a 180* thermostat in my 2k XJ for about 25,000 mile and
still manage to get about 22mpg on the hwy.

Realistically a thermostat will adjust the amount of water entering the radiator
by varing the water flow as the engine temp increases or decreases as you drive.
It doesn't open and stay open. It will close completely below 195*.

A 195* thermostat will begin to open @195* and will fully open @ 207*.
Putting my XJ on a scanner shows that it enters into a closed loop about
175* or so. Once it enters the closed loop - then you can be assured that the
the warmup cycle is off and optimum mileage is being attributed to fed-gov
unless you are in "wide open throttle mode" and in that mode all bets are off
with the optimum mileage. If it stays in the warm-up cycle(>175*) too long you will get a MIL.

A verification with these points can be done with in the FSM section 7 Cooling System
and 14 "Fuel System" sections.

Eddie

eddieeddieg said:

I've been running a 180* thermostat in my 2k XJ for about 25,000 mile and
still manage to get about 22mpg on the hwy.

Click to expand...

Man... I wish I was still getting that. I've gone from 22mpg (highway) when I bought the thing in February to around 15mpg everywhere now. The air filter's been changed out, fluids replaced, did the TPS when I killed that hitting some unexpected water faster than I should've - and still 15mpg. Is there any secret to getting the mileage these vehicles are meant to? I'm running totally stock on the tires, gearing, etc., so I'm not quite sure where the problem is.

A 195* thermostat will begin to open @195* and will fully open @ 207*.

Click to expand...

It looks as though this is now what I'm seeing after having changed out the coolant. I decided to do this ahead of a thermostat swap, and I now run at 195 in motion, hitting 210 or so in traffic with the A/C running. It's gone a bit above that a couple of times, but the electric fan was able to bring it down, something that didn't happen before the flush & fill. My panic is subsiding, slowly

Having said that, I do still plan to do the LeBaron hood vent conversion - since my problems seemed to pretty much revolve around dead coolant, it makes sense to make the coolant's job easier overall in the future by venting more heat out of the engine compartment.

Also: I really liked the spacer adaptation, but had some reservations about it due to the fact that I have to park in some really seedy places for work every once in a while; the prospect for vandalism seemed too great with it. Granted, the vents aren't necessarily more secure, but are probably less of an attractive nuisance than a jacked-up hood with a visibly-open gap. One other thing: I decided to go with a rear-biased mount on the vents. My main problem is at lower speeds (read: trails, traffic), and given the natural tendency of heat to rise and the upward slope of the XJ's hood to the rear this seemed the most beneficial for my needs.

Putting my XJ on a scanner shows that it enters into a closed loop about
175* or so. Once it enters the closed loop - then you can be assured that the
the warmup cycle is off and optimum mileage is being attributed to fed-gov
unless you are in "wide open throttle mode" and in that mode all bets are off
with the optimum mileage. If it stays in the warm-up cycle(>175*) too long you will get a MIL.

Click to expand...

I need to get an OBD-II reader. The post-smog cars I've owned prior to the XJ have all had a way of blinking their codes out through the Check Engine light; not being able to do that here is really annoying.

Thanks for the pointers, btw. It is much appreciated, and good to know that I can run cooler without any major issues.