Strange Overheating Issue

[cwyman6]

Backpressure can be tested using a back pressure tester. Screws into the 02 sensor bung. Make sure u put it in the upstream sensor hole. Rev the motor up to redline while looking at the gauge. Should not exceed 6psi.

 

[RCP Phx]

By your description of when it happens I'd be suspicious of the map sensor also!

 

[Slimer]

My bad, the mechanic I took it to tested the catalytic converter and visually put a bore scope in the bung.

 

[burntkat]

A plugged catalytic converter? How do I test for that? I doubt anyone has looked at that yet.

Bring vehicle to operating temp, use an IR heat gun ($20 tool, ought to be in every good wrench's toolbox) to check temps fore/aft of the catcon.

I can't tell you what to look for specifically just yet, but I think there is a drop expected. Google would help there.

 

[burntkat]

My bad, the mechanic I took it to tested the catalytic converter and visually put a bore scope in the bung.

You won't necessarily see anything in the catcon even if it's plugged, depending on the type of element bed inside it.

If it was me, I'd be awfully tempted to remove the catcon, replace with a straight pipe, and run the real world test (take up the mountain) and see what happens.

Strictly for testing, of course, and sure, replace it afterwards....

 

[Slimer]

I gave up and took it to the mechanic this morning. I will let you all know what he says. Thanks for the help!

 

[Slimer]

Well, you guys aren't going to believe this; but, all they did was replaced the fan clutch! They said that the fan clutch was partially working, but was "sweating", so they changed it out. I went and drove the snot out of it and no overheating.

I thought the fan clutch didn't do hardly anything at highway speeds, I wonder why it stops the overheating issue on the highway then. Also, why would it cool off so quickly when I got out of the gas and coasted? I mean it took 30 seconds to cool off.

 

[Green XJ Jeep]

The fan clutch will engage when it gets to a certain temp.
Maybe for some reason there isnt enough airflow through the radiator and the fan is need to draw in more air?
Good job on figuring it out

 

[Slimer]

Hopefully, that was the only problem. We checked everything we could think of.

 

[burntkat]

Well done. Sounds like you have a good mechanic out there. They're hard to find in this area!

 

[Slimer]

Well, the strange overheating issue is back, but only when going up the mountain, under a load (maintaining 65 MPH).

I think the problem is somehow electrical since I have tried/checked everything else.

About once out of every 50 times starting it up, the interior is dead except the "Airbag" light comes on the dash, everything is dead. The windows, guages, HVAC, etc... are dead. I turn off the Jeep and start it up again and everything is fine. Could this be related to the overheating issue.

 

[burntkat]

I don't see how an electrical issue could be causing overheating while going up the mountain.... unless maybe the transmission is not shifting properly (t's an electronically-controlled transmission, so possible). But I think you'd notice that in driveability.

 

[Slimer]

I don't see how an electrical issue could be causing overheating while going up the mountain.... unless maybe the transmission is not shifting properly (t's an electronically-controlled transmission, so possible). But I think you'd notice that in driveability.

I thought maybe the engine is running lean or something. I really don't know.

 

[RCP Phx]

Have you checked your tranny line temps when this is happening? Have you checked to be sure about the gear ratio?

 

[Slimer]

I have never checked the tranny line temps, what will that tell me?

The gear ratio is 4.56 for sure. I have a Ford 8.8 in the area and a Dynatrac Prorock44 up front.

 

[RCP Phx]

Since you have the issue under heavy loads/incline your tranny might be overheating and that does affect engine temps. What aux cooler do you have and is it being used with the rad cooler? You can p/u a wireless 2-input thermometer for 30$, they are great for measuring trans lines, rad hoses, tank temps and more! Has the speedo been correct for the tire size? How have you confirmed the gear ratio, you just bought it?

 

[Slimer]

Yes, I checked the gear ratio and the speedo is very close also.

It has a small aux trans cooler in the front of part of the radiator. I will check it with my infrared thermometer first.

Would the fact that the catalytic converter has been hollowed out make a difference? I don't get any codes, but I did cut the tailpipe direction after the cat and found it to be hollow. I welded it all back together. Could it be a bad o2 sensor or MAP sensor?

 

[RCP Phx]

What aux cooler do you have and is it being used with the rad cooler?

Is a plate or tube style? How many passes? How is it tied into the system? What's it's placement in the grille?

Would the fact that the catalytic converter has been hollowed out make a difference? I don't get any codes, but I did cut the tailpipe direction after the cat and found it to be hollow. I welded it all back together. Could it be a bad o2 sensor or MAP sensor?

You were asked all that 2 weeks ago, you said you had the cat tested and was good? You also said all the sensors were good although you never posted any data?

What else haven't you told us?

 

[RCP Phx]

Have you spoke with the seller/builder, he could be a great asset?

 

[Slimer]

Is a plate or tube style? How many passes? How is it tied into the system? What's it's placement in the grille?



You were asked all that 2 weeks ago, you said you had the cat tested and was good? You also said all the sensors were good although you never posted any data?

What else haven't you told us?

It is a flat style aux cooler with two rows. I will have to check out it is plumbed.

Well, I can only go by what I was told. As far as I know, no one has installed a data logger on the system and driven around with it hooked up. According to the mechanic I took it to it throws no codes and everything was tested in range on the scope. I was able to verify some of this with my OBDII bluetooth adapter. Since it is not a problem that is present at all times I was asking if one of these sensors or something could have an intermittent problem. What data do you want me to post? Where do I get such data? I don't own diagnostic scanner and I doubt any mechanic is going to download the data for me. Tell me what data you want? I have also cut holes in the hood and added Napier hood vents in the last week. It has fiberglass fenders on it. Other than that it is green.