coolant temp/ engine swap need help

hey all,

just bought a 1989 MJ with the renix computer and the previous owner swapped in a power tech 4.0 from a 1997 TJ. the MJ is running the old sytle cooling system with the pressure bottle. the coolant temperature sensor is located in teh thermosatat housing, since its the power tech engine.

the temp reads consistently at 220* but, the hood feels cool to the touch, the engine does not feel hot and the coolant seems warm, but not boiling over. IMO, it doesnt seem like its running hot.

can this be out of whack because the computer/ engine are different? thanks for any input.

-tim

It's a little over design temp, but not so much that I'd worry (if it's consistent.)

You might want to give the cooling system a good flushing, just to break up any scale and crap that might be in there. That should help to drop your operating temperatures slightly - but design temp is 210-215 anyhow.

As long as you can get airflow over the cooling system elements, the hood should not get hot - my hoods don't heat up, and I've got four of them.

The design of the RENIX cooling system is just fine - I'm working on a FAQ writeup for all the cooling systems, as well as tips and tricks - but the only reason the second 89 that I got is converted to an "open" system is just because I got it that way (I'd have put a little more engineering into it, but that's just me...)

5-90

ok, we tested the sensor in a pot of hot water with a household thermometer. when the water was warm (160*), the jeeps guage read about 115*, when the water was hot (200*), the jeeps guage read about 220*. so, it doesnt exactly read right.

does anybody know if the resistance between the renix CTS sensor is the same as the power tech's sensor?

i think the power tech's CTS is confusing the jeeps renix computers.

-tim

The coolant temp sensor for the computer and the gauge are not the same for your 89 MJ. The temp sensor for the computer on a renix era XJ is on the side of the engine block, under the intake manifold. The sensor for the gauge should be in the head, on top but near the firewall, it should have just one wire. If it really is a 97 block and head, there won't be a hole for the gauge sender unit in the back of the head. So from your post I am assuming the guy used the TJ coolant temp sensor in the t-stat housing for the gauge sender unit? That sensor is designed for the computer and like you said, it probably doesn't read correctly. Might want to get a new temp gauge sender unit and adapt it to fit into the thermostat housing.

yeah, you would be correct. the CTS on this jeep is in the thermostat housing, rather than on the back of the engine, and the cooling style is still the old style, so its a mix and match, but other than the temp, everything runs perfect, idles a little high.

-tim

Did the previous owner swap the computers too? So you should have the OBDII PCM.


Kyung

no, it is running a RENIX computer.