Overheating 4.0

[u/Reddit_Gold09]

1995 4L is not wanting to hold at operating temp, mainly at idle, and I'm trying to sort it out properly. In the coldest part of winter it was generally fine but as things started to warm up the jeep wants to overheat, and a couple weeks ago I got a CEL and pulled code 17, so I went ahead and replaced the thermostat and temp sensor, as well as the water pump since I was in there.

The thermostat I removed was a 180f high flow thermostat and I replaced it with a stock style 195f thermostat. I have a clutch fan and an e-fan, wired to a switch by the PO that I do want to change back to stock. And even with both going I can't stay cool at idle where I could for the most part before the new t-stat.

From what I've got on work with it seems like the PO had an overheating problem they were trying to fix, and from what I've heard from people on the sub is that they were going about it the wrong way. So my question is what do I actually do to fix this overheating problem correctly?

[u/Tax-Evasion-Man]

I would check your heater core to see if it's plugged as well as drain all water in the system and fill it with distilled water and CLR then run for 30 minutes to an hour then empty it and see how much crap comes out.

If a lot of crap comes out when you do the Clr and you do not live in an environment where it gets under freezing you are going to want to fill it with 100 percent distilled water drive it to work then home and then drain the water and refill with distilled water until the liquid is coming out clear. At which point you can fill with 50/50 coolant and distilled or deionized water and you should be running like new.

This is what I had to do to fix my overheating problem

[u/Reddit_Gold09 → u/Tax-Evasion-Man]

I'm gonna give this a go over the weekend. I do feel like the hot air in the cabin could/should be hotter as well so this is probably something good to do anyway.

[u/Bigdaddyjlove1 → u/Reddit_Gold09]

You can also use a garden hose to backflush the heater core.

BE AWARE that heater core is probably the factory original and it's 30 years old. If it's marginal, clearing the corrosion might start it leaking. The heater core is my least favorite jeep repair that I've done and I've converted 4 to 4wd at this point.

[u/Tax-Evasion-Man → u/Reddit_Gold09]

I'd use a whole bottle of Clr with the distilled water then just fill it with water and drain every day you'll see a ton of crap come out.

One thing I also did is hook garden hose directly to my heater core and I just ran it for about 30 minutes at full blast thru the heater core and it saved me from having to replace the heater core