258 running too cool

[Oregonite]

I have a '74 CJ5 with a AMC 258 i6 / 4.2l and installed a mechanical temp gauge and the scale begins at 130 degrees. After driving it the reading is 135-140 degrees. I have a 195 thermostat in it. I checked the thermostat in a pan of water on the stove and it is opening and closing correctly. I used the original location where the factory gauge was. Why won't it register hotter?

 

[Torxhead]

Looks like you might need a better place to put the sender, as it does not appear to be deep enough into the head. I believe there is a thermostat available for the 4.0 with a location for the sending unit. I have mine in the intake manifold and it reads low also. You could also check that sending unit in a pan of hot water also with a meat thermometer.

 

[Lumpy Grits]

99% of the time when a t'stat 'dies'. It sticks in the wide open position. How long have you seen this very low reading? I wouldn't drive it till you correct this issue, as it will build up sludge PDQ inside the crankcase.
Try a new t'stat. Just get a std 195* one. Don't want/need any of the fancy ones out there.
If the senders location is at the back of the head on the D/S side. That was the OEM spot for many years. That's where mine is on my '85.

LG

 

[Oregonite]

99% of the time when a t'stat 'dies'. It sticks in the wide open position. How long have you seen this very low reading? I wouldn't drive it till you correct this issue, as it will build up sludge PDQ inside the crankcase.
Try a new t'stat. Just get a std 195* one. Don't want/need any of the fancy ones out there.
If the senders location is at the back of the head on the D/S side. That was the OEM spot for many years. That's where mine is on my '85.

LG

This is the stock location of the original electric sender on a '74.

 

[Oregonite]

Looks like you might need a better place to put the sender, as it does not appear to be deep enough into the head. I believe there is a thermostat available for the 4.0 with a location for the sending unit. I have mine in the intake manifold and it reads low also. You could also check that sending unit in a pan of hot water also with a meat thermometer.

The sender is in the coolant at that location. It is in the same area as it would be with a 4.0 thermostat housing. I will check the sender in a pan of water with a thermometer. I have already tried another mechanical gauge and end up with the same reading.

 

[Lumpy Grits]

Pull the t'stat and test it, if it isn't stuck open.......
LG

 

[Oregonite]

Pull the t'stat and test it, if it isn't stuck open.......
LG

Pulled it and tested the 195 degree thermostat and it is opening and closing. It was closed when I pulled it and opens at 200 degrees in a pan of water on the stove and closes when it cools down. I am going to put a piece of cardboard in front of the radiator and see it the gauge will respond to that. It is a warm day (80's)

 

[Lumpy Grits]

It should only start to open at 195-200* and not be all the way open till around 215* or so.
Is this t'stat marked with the temp?
BTW: I have seen a trapped air bubble in a cooling system cause low readings when that 'bubble' is covering the temp sensor.
You don't have any Teflon tape or such on the temp. sensor threads do you? T'tape will cause false readings because it impairs the grounding that the sensor must have to read 'rite'.
LG

 

[Torxhead]

I would think the drilling the hole in the thermostat trick would help in getting the air out if that is a problem. Driving up and down steep hills can also help with getting the air out. Lumpy, this is a mechanical gauge so the Teflon tape should not be an issue here. On the instructions for my mechanical gauge unit it does state that the sensor must be in circulating coolant for an accurate reading. Looking at Oregonite's pic it does appear that the small tube going into the head could affect the coolant from circulating around the sensor.

 

[Lumpy Grits]

T'head-YOU are 110% 'rite' about t'tape not an issue on that MECHANICAL sensor.

LG

 

[Torxhead]

T'head-YOU are 110% 'rite' about t'tape not an issue on that MECHANICAL sensor.

LG

I did test the gauge by putting the sensor in a pan of hot water with wifey's meat thermometer and it was accurate. The instructions that came with it did not state that I could not use Teflon tape with the mechanical gauge, but did state not to use tape with the electrical version. On my last trip to the Panamints I did have an overheat which did not register on the previous electrical gauge as overheating, but did stall the engine. Doing the thermostat test it failed to open properly.

 

[Oregonite]

Looks like you might need a better place to put the sender, as it does not appear to be deep enough into the head. I believe there is a thermostat available for the 4.0 with a location for the sending unit. I have mine in the intake manifold and it reads low also. You could also check that sending unit in a pan of hot water also with a meat thermometer.

Torxhead, I think you are right about the sender not far enough in the head. On this engine the only place for a temperature gauge is in the front of the head and it is only an 1/8" hole for the factory electric sender. I have an Offenhauser intake with a Holley 390 four barrel and there are no provisions for a temp gauge on that intake. I found out that the factory gauge was not even hooked up on the rear of the instrument cluster, so I will see if I can get the factory gauge to work. I wanted to run a mechanical gauge but I'm stuck with the factory electric setup. Hopefully it will work for me when I get it changed over. I put a test light on the wire end that plugs onto the sender and the test light blinks on and off. Is that normal to do that?

 

[Torxhead]

Here is some help for the gauges:
The new Gauge Page
Another possible location for a mechanical gauge sender is in the side of the block, below the head. Although by now the threaded plugs are well rusted over. Looking at a wiring schematic for your rig, I see a purple wire coming from the temp sending unit going to the gauge. I am not sure why the test light blinks though. It does work along with the fuel gauge and one can affect how the other operates. There is a replacement kit available that includes the fuel gauge, temp gauge, senders, with instructions probably from one of the big box 4wd outfits.

 

[Lumpy Grits]

Torxhead, I think you are right about the sender not far enough in the head. On this engine the only place for a temperature gauge is in the front of the head and it is only an 1/8" hole for the factory electric sender. I have an Offenhauser intake with a Holley 390 four barrel and there are no provisions for a temp gauge on that intake. I found out that the factory gauge was not even hooked up on the rear of the instrument cluster, so I will see if I can get the factory gauge to work. I wanted to run a mechanical gauge but I'm stuck with the factory electric setup. Hopefully it will work for me when I get it changed over. I put a test light on the wire end that plugs onto the sender and the test light blinks on and off. Is that normal to do that?

How does the length of your newer sender compare with the OEM one?
If you do go with another gauge. I have installed these for friends, and I'm impressed with them.
2-5/8" Water Temperature Gauge. Black Dial, Mechanical Water Temperature Gauge.
LG

 

[Oregonite]

I installed the original electric temperature sender and using the original gauge in the speedometer cluster. It reads just above the cold line when the engine is at operating temperature.

 

[Torxhead]

On my CJ I run one of each type of gauge. With a 180 thermostat, at operating temp the electric gauge reads right in the center of the scale. I like having a backup gauge.

 

[Lumpy Grits]

Oregonite-Please see my post #8.
At what temp was the t'stat all the way open?
Most t'stats have markings on bottom of the center sleeve to show what temp they are. Did yours show this?
I know you've done a lot of dig'n here. I would suggest that you go and just get a standard Stant 195* t'stat and give it a go.
Good luck,
LG

 

[hagar]

Temp sender wire will pulsate just like the fuel sender wire will when tested with test lamp.
The voltage is being reduced/controlled by the instrument voltage regulator built into one of the dash gauges, don't recall which one has the regulator built in.
The pulsing would be considered normal.

 

[mtnwhlr]

I would suggest that you go and just get a standard Stant 195* t'stat and give it a go.
Good luck,
LG

and make sure you aren't installing it backwards and as said before drill a small hole in the base.

 

[Oregonite]

I am still getting a low reading on my temperature gauge. The gauge cluster in my '74 CJ5 was replaced with a VDO gauge cluster. Do I need to buy a new VDO sending unit to get a correct reading on my temperature gauge? I found this article https://summitracing.custhelp.com/a...mixing-different-brands-of-gauges-and-senders