Running hot

F

Feral

New Member
Joined
Apr 29, 2021
Messages
7
Location
Earth
I just replaced the head on my 4.0 and it was running hot, around 235 F.

I replaced the following trying to figure it out:

Temp sender x4
Waterpump x1
Radiator x1
Thermostat x3

I flushed the block and replaced the hoses.

i finally bought a radiator cap with a thermometer in it.

It showed I was running about 155 F at the cap.

After much searching online, I ordered an OEM temp sender.

That $17 part fixed it.

I bought 2 senders from NAPA, 1 from Autozone and 1 from Rockauto.

Thier mistakes cost me over $1000.
 
Feral said:
I just replaced the head on my 4.0 and it was running hot, around 235 F.

I replaced the following trying to figure it out:

Temp sender x4
Waterpump x1
Radiator x1
Thermostat x3

I flushed the block and replaced the hoses.

i finally bought a radiator cap with a thermometer in it.

It showed I was running about 155 F at the cap.

After much searching online, I ordered an OEM temp sender.

That $17 part fixed it.

I bought 2 senders from NAPA, 1 from Autozone and 1 from Rockauto.

Thier mistakes cost me over $1000.
Click to expand...
That is too bad, sounds like something I would do. Try to look at the good side....at least you know you have some good stuff already installed
 
I'm a little confused at the sequence. Did and actual high temp cause a problem with the head or were they just false readings?

One thing I've read and did experience with 4.0L XJ is air can get trapped in the head and cause overheating and cracking. This came from a dealership and their experience and the YJ may be the same.

Anyhow it's very important to ensure all the air is out of the cooling system and it may not work it's way out over time. The best thig to do is "burp" the system and an easy way to do it is raise the front end by parking on a slope or ramps, open the radiator cap (when cool), start the engine and make sure it's full with no more bubbles coming out.

It's worth doing anytime you open up the cooling system byt changing the coolant, pump, hoses of other work requiring you to drain the the system.
 
Feral said:
I just replaced the head on my 4.0 and it was running hot, around 235 F.

I replaced the following trying to figure it out:

Temp sender x4
Waterpump x1
Radiator x1
Thermostat x3

I flushed the block and replaced the hoses.

i finally bought a radiator cap with a thermometer in it.

It showed I was running about 155 F at the cap.

After much searching online, I ordered an OEM temp sender.

That $17 part fixed it.

I bought 2 senders from NAPA, 1 from Autozone and 1 from Rockauto.

Thier mistakes cost me over $1000.
Click to expand...
Where did you order the OEM part at? Can you share the part number? I may be having the same issue.
 
Silb said:
Where did you order the OEM part at? Can you share the part number? I may be having the same issue.
Click to expand...
Found mine on Amazon. I never installed because the seding unit from Crown hasn't caused me any issues yet. My heating issue ended up being a failing water pump and a broken replacement Crown temp gauge. I replaced this with a used OEM gauge from ebay.

I believe you are suppose to test the temperature at the rear of the head by the sending unit.

Mopar Sending Unit from Amazon:
20211231_070720.jpg

20211231_070738.jpg
 
You will have to clean the masking off the threads though. You must have clean contacts for a proper ground when the sending unit is in the head.

I would advise not using a deep socket to install. I ripped two Napa one's in half doing it. Use a wrench until the unit is tight. The threads are tappered, so it may not be flush with the head. I have a small gap for mine
 
Top Bottom