Hello everyone. My question is about possible after market replacement part numbers for the two temperature sensors located in the thermostat housing. One being for the glow plug circuit and the other for the fast idle circuit........I have been robbing them from spare engines and have not done any research for them.........

thanks in advance,
crossbones

Bones,
Good idea and I'm glad you are looking for that info.
Frankly they may become totally non-available soon givent he age of some of our vehicles. (I hanve an 81 Pup).
It may also be a thought to measure the characteristics of the sensors (thread size, on and off temperature, length of "probe") and use that info to find a different make all together. Even if the "new replacment was sized differently a threaded adapter could be used to screw it into the existing hole. (assuming the new was smaller)
Well enough babbling...
Eric

I'm not sure if it's relevant, but my 4BD1T takes the same temp sensors as every other japanese engine.
I think they're a M14x1mm thread, but I can't verify that right now.

I have four ports all the same thread, but varying depth (due to internal thermostat interference) one below the thermostat, and three in the housing above.

The temp switch I use for my electric fans is also the same thread and is interchangable with the temp sensors.

I'd also add that my 4JB1 sensors run the gas Trooper gauges perfectly well, which leads me to believe the engine sensors are the same on both engines. Much cheaper for Isuzu this way - wonder what sensors cross over from other Isuzu models? The glow plug sensor is on/off, so maybe look for an electric fan switch from a gas engine?

Do you know what temp they switch at?

Although being on top of the thermostat, as soon as it opens you'll get 90 deg C (or whatever it's running at) water all over it and it'll probably switch anyway.

Looking at my 4JB1 manual, the thermoswitch for the glow plugs should switch ON (have continuity between the wire and the body) between 44-55* F (7-13* C) and switch OFF (no continuity) below 37* F (3* C).

Hi All--

I don't have any replacement part numbers. But, I do have some experience with failed glow control temperature sense switches. Twice, I have had my plugs fail to glow with a cold engine and both times it was because the sensor had developed a leakage resistance from the switch terminal to ground. I measured this resistance to be in the range of 20k to 50k ohms. One would not expect this to be a problem with a circuit designed to sense a switch closure but it is for the Isuzu glow controller (QOS, Isuzu calls it).

I have taken these sensors apart and cleaned up the interior terminal area and this eliminated the leakage. This is a tedious job. If any one wants to try it I can post some details.

I have also figured some QOS circuit changes which will desensitize the the circuit to leakage resistance down to about 4k ohms. This should extend the usefulness of a leaky sensor quite a bit. I can post this as well.

Also, the wiring diagram for my '84 diesel shows the operating temperature of the glow switch to be 15 degrees C., same as Dougal says.

Paul

Edit-- Same as acy76 says. Sorry

Edit, again-- I was looking at the fast idle switch on the wiring diagram as 15 degrees. The glow sensor switches at 50 degrees C., which, I think, makes more sense.

Paul

Hello Paul. Please do post the information on repairing the sensor and the QOS box modification........

thanks in advance,
crossbones

Hi crossbones & All--

OK, thanks for your interest. I will put together a tutorial of sorts and post it as soon as I can.

Paul

Yes sir, please do pass on the technique for rebuilding the temp/glow/switch. I think it's really great when this kind of DIY project works. It's even feels better someone else appreciates the process.
We do know that it often take just as long to document a project like this as it does to do it.
Thanks for takin' the time.
Brian Rodgers <img src="/forums/images/graemlins/cheers.gif" alt="" />