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Discussion Starter · #1 ·
I am finishing up a 2.5L to 4.0L swap. Everything went well, and it's running perfect. Of course, there's a few items to tidy up.

The only major issue that I'm having is that my engine temps are much higher than before with my 2.5L. I'm seeing temps creep up to 230-240 or so. This is just after a 5-10 minute idle in my garage, which is probably 75 degrees. The 2.5L never went over 200-210 or so, even in the summer.

It's a used engine out of a 1998 TJ. The water pump and thermostat are original to the engine. (I already have a new thermostat and gasket - I just decided not to install them until I needed to do it)

The radiator is the same one as before - it looks pretty thin. The radiator portion is much thinner than the plastic top/bottom tanks. It's tough to measure or get a picture, but it looks like the fins are only 1/2 the width of the tank.

All hoses are new. Coolant is new and filled up. 50/50 mix.

Fan clutch is original to the TJ. It appears to be working fine - it has resistance when rotated.

Fan shroud was replaced - it is out of a 4.0L YJ.

Thoughts? Suggestions?
 

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1998 would be a OBD2 system, and yours was an OBD1. So, the sensors would have to match the PCM, which in turn wouldn't match the gauges.

If I recall correctly, the OBD2 system gauges get their readings from the PCM, and on the OBD1 they get them from the sensors.

Kind of like the VSS on an OBD2, the signal goes to the PCM, then over to the speedo.

I could be wrong, but I believe that's how it works. You might want to get aftermarket gauges to get true readings from the motor.

And the single core radiator will work ok on flat ground, but pulling hills or rock crawling its going to run hotter because of the lesser cooling capability of the single core.
 

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You have a single core radiator...You need a dual core for that larger engine.. I put a dual core in mine just for the hell of it... No problems since.

my dual core rad ebay special 80 bux new.
 

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If sensors aren't the issue and it really is getting that hot, there could be an air pocket or maybe the Tstat is frozen up.
 

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Air pocket - what's the fix? I'll try the cheap and easy stuff first.
I just had that issue on mine after a water pump swap. Jack up the front end and take off the radiator cap. When its cold! And run it. That'll work all the air out. I managed to get a few more quarts of coolant in afterward. I stood there slowly pouring in as the air worked out. It makes a bit of a mess if it bubbles over but keep at it till temp is normal again.
 

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If it is an air pocket easy fix I used was jack front end as high as you can and open radiator cap and crank engine let it warm up air should rise to highest point which should be the cap.

Make sure heat is running

Can also remove each temp sensor one by one to make sure no air pockets though I did not do this.

Chief
 

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Discussion Starter · #10 ·
I'll try to fix any air pockets tonight - quick, easy and free.

Depending on how that goes, I may just replace the thermostat.

I'd rather not spend any more money on a radiator, unless it's really needed - this swap has already been somewhat expensive. Worthwhile, but expensive :drinks:
 

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Discussion Starter · #11 ·
No air pockets...the gauge is just reading wrong, for some reason.

I checked the resistance of the sensor, and it is correct. I used a thermocouple on the upper radiator hose to get the "real" temperature, while measuring the resistance of the sensor.

The gauge was fine before the engine swap, so I'm a little baffled.
 
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