Cooling system question.

[SanDiegoOverland]

I have a 92 OBD-1. For giggles I tried the ignition switch diagnostic, after replacing my radiator, as I was seeing the engine running cooler than usual.

Sure enough, it threw this code:

17 - Engine stays cool too long



Symptoms:

-engine runs cool 150-175 or so
-heater blows mostly warm
-mpg have dropped to around 16-17 from 20-22mpg when I initially bought the jeep 6 months ago.

I've replaced these parts:

-Orig. radiator ruptured plastic tank - Installed alum core radiator, new coolant, upper and lower hoses. Problem solved.

-Engine cut out at highway speeds, as I lifted the throttle - Traced it to the TPS, and found dead spots with a multimeter. New TPS installed. Problem solved.

Thats it, other than tune up items that did not include the cooling systemcap, rotor, plugs, wires, fuel filter)

Would you say my error code has to do with the older/possibly original thermostat sticking open and keeping the engine in "cold start" mode? I've read that it can have a strong effect on mpg due to the "choke' staying open to help a perceived cold motor warm up.

Or possibly the alum core radiator cools THAT MUCH better and some how a lower temp thermostat had been installed by the P.O. to solve hot running issues?

thanks for any insight. I'll likely order a factory thermostat(I've heard aftermarket ones are junk) and gasket, anyways, just so I know that its good.





-

 

[birchlakeXJ]

The thermostat is absolutely suspect here. You need to get the engine temperature back in the 200 degree F range (give or take a few). You are running way too cool.

I would start with replacing the thermostat as you indicated you plan on doing. Sounds like it needs one anyways so that is job #1. I definitely agree with you that factory stats are of high quality. Stant "superstat" is also a good quality thermostat.

If after replacing the thermostat, you are still running too cool, then you should test and or replace your cooling temperature sensor. If that sensor is bad and is providing incorrect input to the computer, you can have symptoms such as you describe. The resistance in the sensor is high when cold and drops about 300 ohms for every degree Fahrenheit as the sensor warms up. This alters the return voltage signal back to the computer which the computer then reads to determine engine temperature.

Because of the coolant sensor's central role in triggering many engine functions, a faulty sensor (or sensor circuit) can cause a variety of cold performance problems. The most common symptom is failure of the system to go into closed loop once the engine is warm. Other symptoms include poor cold idle, stalling, cold hesitation or stumble, and/or poor fuel mileage.

Once your temp comes up, reasonable gas mileage should return.

Good luck and let us know what you find; we're always interested in solutions!

 

[winterbeater]

X2 on the tstat. I'd get the Stant premium. After working with the OEM's, I wouldn't count on the quality of the dealer parts, especially parts like tstat's and radiator caps. I could elaborate on this with many tales of warranty experience, including Chrysler.

 

[SanDiegoOverland]

excellent. thanks gents. I'll go ahead with the t-stat install and report back. I'm thinking that'll likely make a major difference...

If not, I'll continue on to the coolant temp sensor.

-Brian

 

[SanDiegoOverland]

X2 on the tstat. I'd get the Stant premium. After working with the OEM's, I wouldn't count on the quality of the dealer parts, especially parts like tstat's and radiator caps. I could elaborate on this with many tales of warranty experience, including Chrysler.

where are you guys finding stant t-stats? I just checked morris4x4 and quadratec and I don't see any specifics...

would I find them @ napa or vato-zone?

 

[birchlakeXJ]

Napa would definitely have stats; I don't know what brand they carry though. Ask for a premium stat wherever you go and make sure it has a small bleed hole which goes to the top when installed. I have had very good luck with stats purchased directly from Jeep.

 

[winterbeater]

Or just order from rockauto.com. I don'r remember for sure, but they are probably 4 bucks. Usually good prices, just need to figure out what else you need like Wix oil filters or whatever to cut down on the shipping.

 

[joe_peters]

Vatozone? No, if it ain't Cheapo import they don't stock it, and that's a fact, Jack.

Napa around here only carries their own brand, no Stant.

I pick my Stant stuff up at the local independents.

 

[desertrandy]

I just ordered a Stant Premium 195 degree from kragen today. It was 10.99. You can order them online at www.kragen.com and have them shipped.

 

[SanDiegoOverland]

thanks guys. just called pep boys down the street (very nice store. huge, with 3 or 4 guys who actually know their stuff)

they carry stant premium (195 degree) for 7.99 and have gaskets, too. I'll probably go manana and pick one up.

 

[SanDiegoOverland]

UPDATE:

Stant premium stat is installed and the rtv/gasket is curing as I type this. I have to say that I've worked on cars all my life and XJ's continue to floor me with their easily accessible(for the most part) componants.

I am planning on letting the gasket/Rtv set up over night. Do you think tomorrow morning, 9-10ish is too early to fill? I'd really like to fill and take it for a test drive before a family event happening @ 2pm. Otherwise it'll have to sit until about 6 or 7pm, and I'll have to deal with any issues then.

It was a permatex brand RTV and it said that the silicone will cure in 24 hours. Wondering if I'd be doing myself a disservice by filling and pressurizing early.

 

[joe_peters]

UPDATE:

Stant premium stat is installed and the rtv/gasket is curing as I type this. I have to say that I've worked on cars all my life and XJ's continue to floor me with their easily accessible(for the most part) componants.

I am planning on letting the gasket/Rtv set up over night. Do you think tomorrow morning, 9-10ish is too early to fill? I'd really like to fill and take it for a test drive before a family event happening @ 2pm. Otherwise it'll have to sit until about 6 or 7pm, and I'll have to deal with any issues then.

It was a permatex brand RTV and it said that the silicone will cure in 24 hours. Wondering if I'd be doing myself a disservice by filling and pressurizing early.

What was the temp when you put it together? Overnight? The ambient temp may have an effect on curing time--check the products stats at permatex's website.

 

[SanDiegoOverland]

it was about 70 when I put it together, and its about 60 or so right now. and will likely stay about this temp. tonight.

 

[Dobbs]

Hello my 92 run cold to cleaned the red this summer mine never gets much past the first mark .never gets to the 220 have changed thboth sending units .I just figg I was lucky seems every one s running hot and trying to get them to run cooler.

 

[5-90]

Stant and RobertShaw are both perfectly acceptable aftermarket brands for thermostats - I've used both of them with good results.

Drill the thermostat just like I suggest for RENIX - two 1/16"-1/8" holes, 180* apart, mounted with one hole at 12:00 and the other at 6:00. This takes care of any gas accumulation in the cooling system - from whatever cause (steam voiding, compression leaks, coolant level low, ...)

OBD-I still has two temperature sensors - one in the thermostat housing for the ECU (provides ECU information and E-fan driver signal) and one in the cylinder head (IP lamp/gage driver.) If the gage is reading odd, it's not a bad idea to check using a non-contact thermometer on the thermostat housing - it should read a few degrees lower than the gage as an estimate. If it's significantly colder or significantly hotter, plan on replacing that part (it's a cheap part, but it's a pain to extract. Be very careful! Coat the threads on the new part using RTV copper - it's actually a copper-bearing sealant, and it's worked well for me on self-grounding sensors. Anything else has insulating properties.

(If not the RTV copper, use never-seez. Either way, tighten the new sensor using a socket and no ratchet until it's finger tight, then put a ratchet on it and go one more flat, or one-sixth turn. That's the rule for pipe threads in that size, and the sensor is threaded 1/8" NPT.)

The sensor in the thermostat housing, if it's failed, will cause ECU information to be flawed. The temperature/resistance graph is published in the FSM (it's standard GM stuff,) so that can be checked with a pot of water, a thermometer, an ohmmeter, and a stove. Use whatever you like on the threads of the replacement (I prefer PTFE paste,) as it's a two-wire sensor. Tighten 1-2 flats past finger tight.

 

[SanDiegoOverland]

Alright, so I drove to work today, the longest run (about 25mins) since my test drive yesterday:

>no obvious leaks

>Engine is running at about 190-195 on freeway, and at about 205 on surface streets

>Heater blows like a blowtorch now. yay!

>Looking forward to to getting better mpgs, now that the engine is at the correct operating temp.


My next question is more of an admission of guilt. Running "too cool" has been a problem for at least a couple months. I, honestly, fixed it as soon as I understood the problem, but certainly could should have gotten to it sooner....Consequently, I'm wondering what condition my engine internals are in .

As I understand it, running cool keeps the motor in cold start mode, which dumps a bunch more gas into the motor, to counteract a perceived cold environment.

Am I worried about pronounced carbon deposits on the valves or fouled plugs or anything?

As always, my 4.0L is running strong and smooth, but this is my DD and I like to be as proactive as possible(very sentimental car for me )

Thanks all.

-Brian

 

[Dobbs]

I may need to do this.Mine is a 92 also temp get to the fisrt mark my electric fan never kicks on unless the AC on.Pulled the plug from temp sencor on housing and jump the wires to make sure fan worked .My heater seams fine.I just figg I was one of the lucky ones mine never over heats have seen it get a little past the first mark al most to 210 in mid summer when outside temp is around a 100 and it idled for 1/2 hr or so. I flushed the rad and replaced the thermasot early last summer. Has any one elese have a xj that run coolder that most.

 

[joe_peters]

Alright, so I drove to work today, the longest run (about 25mins) since my test drive yesterday:

>no obvious leaks

>Engine is running at about 190-195 on freeway, and at about 205 on surface streets

>Heater blows like a blowtorch now. yay!

>Looking forward to to getting better mpgs, now that the engine is at the correct operating temp.


My next question is more of an admission of guilt. Running "too cool" has been a problem for at least a couple months. I, honestly, fixed it as soon as I understood the problem, but certainly could should have gotten to it sooner....Consequently, I'm wondering what condition my engine internals are in .

As I understand it, running cool keeps the motor in cold start mode, which dumps a bunch more gas into the motor, to counteract a perceived cold environment.

Am I worried about pronounced carbon deposits on the valves or fouled plugs or anything?

As always, my 4.0L is running strong and smooth, but this is my DD and I like to be as proactive as possible(very sentimental car for me )

Thanks all.

-Brian

Pull the dipstick and give the oil the smell test--does it smell of gasoline? Does the oil look thin? Feel thin? Don't taste it.

My only concern would be if the oil is contaminated it may not do its job very well. Another problem with excessive rich would be fouled spark plugs and carbon deposits on the valves, but if the problem was only for a couple months you should get that blown out in a few hard hot runs. Running too rich can damage the CAT, but again I would just drive it and see if any problems crop up.

 

[joe_peters]

I may need to do this.Mine is a 92 also temp get to the fisrt mark my electric fan never kicks on unless the AC on.Pulled the plug from temp sencor on housing and jump the wires to make sure fan worked .My heater seams fine.I just figg I was one of the lucky ones mine never over heats have seen it get a little past the first mark al most to 210 in mid summer when outside temp is around a 100 and it idled for 1/2 hr or so. I flushed the rad and replaced the thermasot early last summer. Has any one elese have a xj that run coolder that most.

Sounds like it is running normally.

 

[Dobbs]

Ok I think I am going to change the therostat any way.Just from what I have heard all 4.0 run hot 210 to 220 is normal. Took the cap off put a thermonter in it it read 130 after setting in the neck for 10 min the engine had run for 30 min before I done this. I may put an electric fan on it sence it run that cool figg I can get a little HP and get a fu Miles to the gal more.