'04 Liberty overheating only when climbing

[Billwill]

Yeah when I was working on Mainframes I travelled with a Techtronics Oscilloscope in my trunk fulltime!

I should have whipped it when I retired!

 

[Billwill]

per the 2003 service manual, it is controlled by the PCM(?) to a SSR.

I don't have a oscilloscope at home to verify it.

You are totally correct here!

I eventually found in the 2003 KJ Service Manual a very brief description of the Radiator Fan Operation:

There is a Solid State Relay for the fan located near the front left fender.

Pin #1 on this Relay gets +12 volts from Fuse #2 40 Amp in the PDC, Pin #3 gets Ground, Pin #2 supplies pulsed +12 volts to the Fan Pin #1. Pin #2 on the Fan goes to Ground.

Pin #4 on the Relay gets its control from the PCM C2 Pin #12.
The Relay then supplies Pulsed Width voltage to the Fan ie. for Slow Mode it will supply a short pulse of +12 volts and a longer period of no voltage. For medium speed the ratio will be something like 50% ON and 50% OFF and probably at maximum speed the PCM turns the Relay on full time. Like turning a light switch ON/OFF rapidly!

I can only find this system in the 2003 Manuals.

My experience of these Solid State Relays in Computer and Peripheral applications is that they work well in controlling speed but they can break down slowly which cause weird problems.

So this is not relevant to the 2004 KJ in this post but for 2003 3.7 L KJ Fan problems this relay should possibly be replaced!

So I have learnt something new here today...I have not worked in this area on the 2003 3.7 L KJs. Interesting point in the Description of the Radiator Systems they describe the Diesel Engine, the 2.4 L Gasser, the 3.7L Gasser and a 4.0L Gasser!!

Probably lifted off the Manual from one of the other Jeep Models...not unusual!

 

[uss2defiant]

yeah. i think as long as one has that one e-rad fan relay by the wheel well, it'll be PWM.
There was a TSB about replaying the smaller factory SSR with the larger one.

Good luck to OP.

 

[mduclow]

So, I got another thread going about my running hot issue, and it turns out the new motor has a head gasket leak or cracked head, causing the overheating.
I had replaced the radiator after charging the A/C because she started running warm with the A/C on, then she kept taking coolant and pushing air into the system. Culprit is the head gasket or a cracked head.

 

[LibertyTC]

Sorry to hear that. How many miles on jeep? Sounds like inspection time and some hard work ahead. Do you have the FSM?

 

[mduclow]

Sorry to hear that. How many miles on jeep? Sounds like inspection time and some hard work ahead. Do you have the FSM?

Well, it's the new motor, still under warranty, so she'll get fixed on a warranty dollar. Motor has about 8,000 miles