FJ40 Temperature Gauge Range (1 Viewer)

[FJ40Savvy]

Searching on the forum however I was unable to find the answer to the following question.

Specs in the F engine repair manual say the thermostat should open between 166-175 and should be fully open at 194. First time driving for an extended period today and the temperature gauge didn't move. Does anyone know the temperature range of the stock gauge (i.e. if the needle is in the middle of the gauge what is the corresponding engine temperature)? Asking because it didn't start as easily as it did when it was cold. I plan to use an infrared temperature gauge on the next outing to make sure it is reading correctly. PO didn't mention it was an issue.

 

[samatulich]

I think it’s supposed to be right around the first mark. At least that’s where my ‘76 2F sits. You say yours doesn’t move? I’d check the thermostat housing with an inferred thermometer. Make sure the housing is getting up to 180* or so. Then I’d check that the temp sending sensor is hooked up.

 

[FJ40Savvy]

I think it’s supposed to be right around the first mark. At least that’s where my ‘76 2F sits. You say yours doesn’t move? I’d check the thermostat housing with an inferred thermometer. Make sure the housing is getting up to 180* or so. Then I’d check that the temp sending sensor is hooked up.

Thanks That is the information I was looking for. New owner and still trying to figure the squeaks rattles and groans but loving every minute of it so far.

 

[bhsdriller]

Yeah same here mine stay around the first mark and sometimes a little over coming to a stop and idling

 

[Engineer8000]

My 3fe sits around that first mark, maybe a litter higher. I use the 40 series sender for the gauge. Doing the math using the numbers from @bj40green cluster thread, C = 140F, H = 212F, so about mid scale is 176F. I don't think these gauges maintain their linearity that well over time. The gauge should go from C to H if you give it 0 to 6 volts.

 

[FJ40Savvy]

My 3fe sits around that first mark, maybe a litter higher. I use the 40 series sender for the gauge. Doing the math using the numbers from @bj40green cluster thread, C = 140F, H = 212F, so about mid scale is 176F. I don't think these gauges maintain their linearity that well over time. The gauge should go from C to H if you give it 0 to 6 volts.

Wow some light reading about clusters for me this weekend. Thanks for the point in the right direction.

 

[mattressking]

 

[Engineer8000]

based on numbers in the '75 chassis body manual

 

[brian]

From the 75 owners manual

 

[GA Architect]

FWIW: On my '77 I have two temp senders and gauges. One is the OEM temp sender & gauge and the other a Sniper temp sender in the block drain. My OEM gauge sits about the first tick-mark, and that is about 185 - 188 on the Sniper read-out. Evey once in a while after driving in the heat, then just idling, it will creep above the first tick-mark to about 192 (+/-) but promptly goes back to about 185 once I start moving again.

 

[FJ40Savvy]

First Official trip with the family out for Ice Cream. The Temp Gauge was not working. When I got home the temperature of the thermostat housing was 176 and the temperature sending unit measured 30 ohms. Need to start troubleshooting starting tomorrow.

 

[FJ40Savvy]

I think it is the temperature sensor. I disconnected the gauge wire from the sensor and connected a meter between the sensor and ground. I then started the engine. As the engine temp increased, the resistance of the sensor started to drop.

Start up - Open Circuit
85 deg F - 300 ohms
110 deg f - 200 ohms
130 deg f - Open Circuit

Based on the above, I think I have a faulty sensor. I will test the gauge on the weekend.

 

[FJ40Savvy]

Planning on replacing the temperature sending unit this weekend. I know enough to be dangerous when doing mechanical work., the FJ40 and I will be learning together. Here are my questions?

The sensor is located on the top of the engine block. I'm assuming that I need to drain some antifreeze from the radiator before taking out the sensor so that antifreeze does come pouring out of the sensor hole?

I'm also planning on using thread sealer on the new sending unit so that it does not leak. I assume that it is required.

Any help/guidance would be appreciated.

 

[brian]

no thread sealer, the sensor needs to ground to the block