230? Is that right? I've read 218 degrees on the various posts so many times that I guess I just believed it. I'll try to run a test today to see what temp mine kicks in while reading the OBD II.
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Thermostat Alternatives/Brands?
- Thread starter Quailman
- Start date
230? Is that right? I've read 218 degrees on the various posts so many times that I guess I just believed it. I'll try to run a test today to see what temp mine kicks in while reading the OBD II.
comanche91
NAXJA Forum User
- Location
- Sweet Home Alabama
220*-230*, resolution on the dash temp gauge isn't the greatest. And since I'm running two electric fans, I just wanted to control the aux fan when I wanted to. Also it gives me a ready backup if my primary fan goes belly-up.
Right. I was going to test it with an OBD II scanner. I've heard my aux kick in before while monitoring, and it certainly was well below 230.
Nice setup you have there.
comanche91
NAXJA Forum User
- Location
- Sweet Home Alabama
Thank you. It cools quite well and I seldom have to use the 2nd fan.
JeepNoob
NAXJA Forum User
- Location
- Pueblo, Colorado
Normally the temp sensor in the thermostat housing applies a ground to the aux fan to energize it when the engine temp reaches 230* or so. That's too late, when I want the fan on I don't want to wait for the temp sensor input while sitting in a hot summer traffic jam. I've been using the below circuit to do the same thing using a dash switch that applies a ground to ECU pin 31, the aux fan input on OBD1 vehicles. It works great and there are no CELs or other problems as the dash switch simulates the temp sensor ground. For OBD2 vehicles a diode could be inserted as shown to prevent a CEL if it occurs. And of course the ECU fan pin for OBD2 rigs would be something other than pin 31.
Will. NOT. work. On OBDII vehicles. This is the lazy method I mentioned of just splicing in a manually switched ground on the fan relay. When I tried it to see what would happen, I used a jumper wire directly on the back side of the relay. It set a CEL and a DTC. I have no idea how the PCM monitors whether the fan is on or not, but it does.
comanche91
NAXJA Forum User
- Location
- Sweet Home Alabama
So, what was the DTC you got Mr. CAPS? :laugh:
I would assume this is it. Makes sense.......
P1491: Rad Fan Control Relay Circuit
An open or shorted condition detected in the radiator fan control relay control circuit. This includes PWM solid state relays.
I would assume this is it. Makes sense.......
P1491: Rad Fan Control Relay Circuit
An open or shorted condition detected in the radiator fan control relay control circuit. This includes PWM solid state relays.
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comanche91
NAXJA Forum User
- Location
- Sweet Home Alabama
Double post...
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JeepNoob
NAXJA Forum User
- Location
- Pueblo, Colorado
Sounds about right. I only tried it once. CEL was on as well. I specifically remember it was a manufacturer specific code instead of a generic P0___ code.
N8N_99xj
NAXJA Forum User
- Location
- Berwyn Heights, MD
That's good to know. I've been kicking around in my head ideas for installing a thermostatic control for fighting heat soak and grounding the stock relay was my best idea so far. Back to the ol' drawing board...
I'm guessing something that will activate the fan in *parallel* with the stock control is just fine though.
I have a Scangauge hooked up and my electric fan comes on at exactly 220F. I can't remember when it shuts off now but it does a very good job of bringing the temp back down at idle on a hot day.
This product is really great for extra relays and fuses:
https://www.amazon.com/gp/product/B072KJNPHJ/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1
It fits nicely between the stock relay box and the fender. And matches it pretty closely. Enough room for a fan relay and 4 relays to upgrade the headlights - or whatever else you want to do.
I'm going to install a timer on my electric fan as well to let it run after the engine has shut off to help with the heat soak on really hot days. Scan gauge shows a pretty consistent 10-12 degree rise after shutdown.
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
218*F the fan should turn on.
I suppose it depends on the year, how clean your sensor is, and where exactly you're getting that temp reading from. Either way, that's too hot, obviously the factory designed it as a last ditch emergency cool down, much better to keep up with the heat before it gets past 210 than to try and fix an overheat.
Mine usually tends to run pretty cool - right around 195 stat temperature, so anything above 200 starts to worry me. Really no reason to run that hot besides a poor cooling system design and too small of a frontal area for the radiator...
I ran my test with an OBD II scanner over the weekend and found the same. On a 90 degree day, I covered the right side of the grill with cardboard to block some of the main fan's airflow. It took about 5 minutes for it to slowly climb from 195 to 220, and the aux fan had no problem bringing the temp right back down quickly with the main still covered.
I'm not sure what you consider "overheat", but 195 to 220 degrees are perfectly normal temperatures for modern vehicles. 230 isn't even a dangerous temperature as long as you're not loosing coolant, and you certainly shouldn't be with a 50/50 mix and a 16PSI cooling system. Boiling point should be around 250-260 degrees.
I see many people call the XJ cooling system poor, but I've always found it adequate. There's not a lot of overhead for sure, but I can pull a 2800 lb trailer around in 100 degree ambient temperatures and never raise above normal temperatures. Even with a 0331 head, it never causes any concern for me.
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Most vehicles do not run above 200 degrees. The XJ has a poor cooling system design, that's why there are at least ten million "my XJ is overheating" threads. The engine bay and radiator were designed for a 4 cylinder or the old Chevy V6, then Chrysler shoehorned the 4.0 in there without changing the design of the front end at all. The stock cooling system is marginal when it's brand new, add a few years and they simply don't like the heat. The radiator is small and the OEM design isn't good. There are better aftermarket ones available.
You're not going to destroy anything at 220, but it's not good for anything under your hood. It's bad for things like batteries, relays, wiring, hoses, oil, etc. Modern vehicles rarely run that hot...and if they do it's the result of a poor design. The closer you can stay to thermostat temperature, the better. A properly designed and functioning cooling system should stay at thermostat temperature under normal usage, not rise well above it.
Everybody just thinks it's "normal" because they printed 210 in the middle of the temp gauge. That's unusually hot for most vehicles.
- Location
- MilkyWay Galaxy
The parts I copied below are not correct. Most OBD-II vehicles since 1996 are designed to run at 212-220 F, and cycle the E-fans (dual or speeds) between those two temps. The T-Stat opens at the lower temp to get the coolant flowing and stable through the system, before peak temps are reached.
My OBD-II rigs have 195 F T-Stats and run, per OEM spec, at 212-220 F. OEMs designed them to run that hot for fuel economy and low emissions. Better manufacturing, better materials and synthetic oils that can handle higher temps made operating the newer rigs at higher temps possible. For instance my son's Ford 1996, has two fan speeds, the ECU turns the e-fan down to low speed at 212 F, and back to high speed at 220F, It turns the fan to high speed, on all the time when the AC is on, and it runs steady at about 212 F with the AC on. My Daughters Saturn 2001, runs at 220 F all day long for 8 years, AC on or not, that is the factory OEM spec on the 2001 Saturn, 275,000 miles on it.
XJ jeeps were designed to run at lower temps, and do most of the time. My daughters 89 ran the last 8 years with heavy use with no cooling problems. Even with the plastic coolant pressure bottle.
I like running my old jeeps cooler, in part because I live down south in the hot humid zones. Rare to see 32 F here anymore.
I think most jeep XJ cooling problems are self inflicted and age related. The Renix had an upper rad hose and E-fan temp switch location (as the radiator clogs up) design flaw.
My OBD-II rigs have 195 F T-Stats and run, per OEM spec, at 212-220 F. OEMs designed them to run that hot for fuel economy and low emissions. Better manufacturing, better materials and synthetic oils that can handle higher temps made operating the newer rigs at higher temps possible. For instance my son's Ford 1996, has two fan speeds, the ECU turns the e-fan down to low speed at 212 F, and back to high speed at 220F, It turns the fan to high speed, on all the time when the AC is on, and it runs steady at about 212 F with the AC on. My Daughters Saturn 2001, runs at 220 F all day long for 8 years, AC on or not, that is the factory OEM spec on the 2001 Saturn, 275,000 miles on it.
XJ jeeps were designed to run at lower temps, and do most of the time. My daughters 89 ran the last 8 years with heavy use with no cooling problems. Even with the plastic coolant pressure bottle.
I like running my old jeeps cooler, in part because I live down south in the hot humid zones. Rare to see 32 F here anymore.
I think most jeep XJ cooling problems are self inflicted and age related. The Renix had an upper rad hose and E-fan temp switch location (as the radiator clogs up) design flaw.
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Even the OBDII XJs are basically exactly the same as the older rigs, with updated computers. I think most people would agree many of the things that manufacturers have been doing to satisfy the EPA are not in the user's best interest. Even if the engine itself is designed to run that hot, it only puts extra stress on every other component like electronics, plastics, rubber, and batteries. None of those things have changed and they don't like heat. Look under the hood of a modern vehicle and you will find more plastic and wires than anything else. 220 degrees won't hurt the engine block at all, it will just cook everything around it. The temp of the engine bay is just as important as the engine block itself.
Higher coolant temps also make your trans run hotter if you are still using the in tank cooler, make your power steering run hotter, make your brake fluid hotter, etc. None of this is good. It also makes a big difference if it's a car or truck. Obviously cars have a much smaller frontal area for dissipating heat. An XJ is almost like a car with a truck engine. I have several late model trucks from Ford, Chevy, and Dodge...none of them run over 200 even pulling a trailer. Because they have giant radiators.
On top of that modern R134A doesn't run as cool as the old stuff, so the hotter your engine bay is the less A/C you're going to get and the harder your compressor has to work. Many modern vehicles have very bad A/C right from the dealer's lot...thanks to the EPA.
An XJ with a good cooling system functioning correctly should not run at 210+ unless you're under a heavy load like towing. Mine rarely goes above 195 except at idle with the A/C running...that's in 90 degree NC July. It never goes over 200 when moving at any speed. I wouldn't say my cooling system is perfect, either.
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Yes, actually they do run over 200 and no, not everybody thinks that. I think it's normal because I've datalogged many OBD-II vehicles over the years and that experience shows me that it's normal to reach temperatures in excess of 200 degrees.
I will admit that I haven't read all "ten million" of those threads, but it seems to me that the overheating issues I read about in them are always due to a maintenance issue such as a plugged radiator, worn water pump bearings and disintegrating impellers, bad fan clutch, etc. I don't recall constantly reading about issues that are due to design flaws. The youngest XJs are now 16 years old, so it seems logical to me that there are going to be some around now that have poor cooling due to a lack of maintenance and normal wear.
There are also limitations to any stock system, and Jeep owners tend to modify their vehicles and stress them well beyond the design parameters of the vehicle in every aspect--including cooling. That is why aftermarket parts are available for most systems, including cooling.
Mine runs the same. It hovers around 196 degrees normally, and very slowly rises when sitting at a hot idle. When towing a 2800 lb travel trailer, I will see it go up to 205 or so waiting for a stop light.
That seems like perfectly normal operation to me, and great performance from a vehicle that has, in your words, such a "poor cooling system design".
Some people seem to think that a vehicle with a 195 degree t-stat should run at that temperature all the time, which is ridiculous. A thermostat works to control a minimum operating temperature, not a maximum one.
The cold side of my radiator, where the tranmission heat exchanger is, shows temperatures around 170-175 degrees at operating temperature. That is normal temperature for an automatic transmission. At the output oil line, the AW4 frequently gets above 200 degrees, so a 175 degree heat exchanger is still doing its job to cool the fluid.
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