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4.0L overheating

Hi,

I'm having a weird overheating problem and I need a little help. First, the details. I have an 87 YJ and I just finished putting a 4.0L into it from a 96 ZJ donor. The swap went well except that the motor "appears" to be overheating. I am running the new engine with my original radiator (never had heat problems before).

After running it for a few minutes the temp gauge starts to climb up towards red line. However, the engine shows no physical signs of overheating. I can touch the head (front and back) and it's not very hot at all. Also, I can open the radiator cap and actually stick my finger in the coolant for a second or so. The is all while the temp gauge is reading about 210-220.

I thought perhaps the coolant wasn't flowing, but I felt the large hose on top and the two hoses to and from the heater core. All three were pretty warm. The bottom radiator hose was warm too, but not as warm as the top hose (I think). Also the radiator itself was pretty warm indicating at least some circulation.

I've put the front wheels on ramps in case I had an air bubble in the pump, but it didn't help any. Also, I looked in the radiator while the engine was running, and couldn't really see fluid flowing. Should I be able to see this?

Final notes - I have a bit of belt squeal at initial startup, but all the pullies are moving. Also, keep in mind that all this is happening in

15* degree weather.

What do you guys think? Any ideas? Your help is greatly appreciated.

Ryan

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Ryan
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Ryan did pass the time by typing:

Hello..

Wonder if the temp sensor is the same between the older and newer engine. If its curve is different that might be what is throwing your temp gauge off. Does the old temp sender fit in the new engine?

You could check by seeing what a couple of known resistors read vs what the sensor shows.

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Reply to
DougW

? Serpentine belt turning the water pump bassackwards ?

Reply to
L0nD0t.$t0we11

Actually, I just got back from Advance Auto and I may have found the problem. It's related to your suggestion.

When I put the engine in it didn't have a temp sender, so I went to AutoZone and bought one for a 96 ZJ. However, I was at Advance Auto 15 minutes ago and just for kicks asked how much a temp sender was. They had two different models - one was if you had a warning light and the other was if you had a gauge!! I'm thinking that maybe they are calibrated differently and that AutoZone may have given me the wrong one. I hope it's that simple.

Now that I think about it, I should have mentioned that my computer and gauges are from a 93 Wrangler (yes, very Frankenstein I know). Should I have bought the temp sender for a 96 ZJ (what the engine is from) or a

93 YJ (what the comp/gauges are from)?

Also, why is Advance Auto listing two different temp senders for a 96 ZJ? Is there another sender besides the one on the head by the firewall that I don't know about?

Thanks for your help!

Ryan

DougW wrote:

Reply to
Ryan

Reply to
L.W.(ßill)

Ryan did pass the time by typing:

Hard to say. It's entirely possible they had a change in the production run. Warning light sensors are usually switch type that open/close at the overtemp setting. Similar to the oil level sender, either "good" or "not good".

I'd probably check both. If they use the same crossreference part then either would work, otherwise use the sensor made for the computer.

I only know of two temp senders, one is the engine temp and the other is the MAT (Manifold Air Temp) sensor.

Reply to
DougW

I don't think I'm turning the pump backwards because I bought the belt for the 96 ZJ. Plus, all the grooved pullies are touching the grooved ide of the belt. I'll doublecheck it though. Thanks.

L.W.(ßill) Hughes III wrote:

Reply to
Ryan

My wife's '93 XJ 4.0 has two temp senders. One in the t/stat housing with 2 wires, used by the PCM, and another, in the back corner of the head behind the intake, with one wire used for the gauge on the dash.

-- Old Crow '82 Shovelhead FLT 92" 'Pearl' '95 Jeep YJ Rio Grande ASE Certified Master Auto Tech + L1 TOMKAT, BS#133, SENS, MAMBM, DOF#51

Reply to
Old Crow

Are you using the pump for the ZJ engine? If so no issues.

The sender is my guess. No way you can open the rad cap on an engine running at 210 or more, let alone stick your finger in the coolant.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Ryan wrote:

Reply to
Mike Romain

My XJ runs at 100C (212F) plus a bit on hot days idling ... and what then happens is the electric cooling fan comes on to knock the temp down. So from my stock 4.0L experience, the temp is normal (100C), but the fan is required should you exceed it.

Reply to
bowgus

The pump should have had an "R" stamped on the impeller. The pump should be turning widdershins [counterclockwise] as viewed from the front of the engine. The '95 FSM also notes that the viscous fan clutch is unique for the 4.0 in the ZJ's.

The temp sensor at the thermostat housing has a chart of temperature versus resistance that you can check with a cheap meter.

32 F 29.3K to 35.9K ohm 68 F 11.3K to 13.6K ohm 140 F 2.3K to 2.7K ohm 194 F 860 ohm to 970 ohm 212 F 640 ohm to 720 ohm

With the general statement that the temp sensor should read less than 1K [1,000] ohms with the engine at normal operating temp... about 190 degrees.

Reply to
L0nD0t.$t0we11

Thanks everyone for the excellent advice. Just thought I'd update you with my findings.

It looks like the apparent overheating was because of a fault with the gauge itself. I determined this after turning the key to the "on" position and checking the gauge with the engine cold. It read 160 degrees. I unplugged the temperature sender (both of them). Still 160 degrees. The weird part is that after grounding the temperature sensor wire and pegging the gauge for a few moments, it appears to be working fine. Go figure.

Also thought I'd let you know what I figured out on the position of the senders. Apparently the 93 YJ has two *different* coolant temperature senders. One is a switch in the thermostat housing for the computer and the other is a thermistor in the traditional spot in the head by the firewall (this one is for the gauge).

Again, thanks for the help.

Also, if anyone has any questions on the 4L swap into an early YJ let me know and I'll offer what advice I can.

Ryan

Ryan wrote:

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Ryan

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