I keep replacing the manual wtr. temp gauge. Two in two years. I currently have the sending sensor in the block, just below ... the header. Could the heat be destroying my gauges?

I like having it back there at the hotest part of the engine, but would it make a difference if I switched to the sending unit electrical type gauge, and put the sensor in the thermo housing?

 

I thought surely I'd be able to get an answer to a ralatively simple question like this.

 

I put a manual water temp gauge in one of the block drain holes below the headers in a 64 galaxie (390) and it didn't last 10 minutes. pegged gauge and broke it. while stock dash gauge read fine. In my experience surrounding temp makes a huge difference. Manual temp gauge running off thermostat housing in my 78 F-150 read perfect though. so I would keep the manual gauge away from exhaust, my 2 cents

 

Thanks. I've switched to an electric type. I don't seem to have a lot of luck with these temp gauges. I was tightening the sending unit in the block and noticed it was suddenly bent to one side. I didn't think I bent it, but must have. Now when I turn on the key it pegs to 280, and the block is cool to my hand! I'll put in a new sending unit tomorrow.

 

since you guys are talking about temp sensors. I have a question on my '79 four door bronco I turn the truck on (cold block) the truck reads below the C, after about 15 minuets of driving the block is hot but the temp is still reading on C. The radiator is also warm. Is this the gauge? Sensor? problem. It has a 351.
Thanks.

 

I'm a bit perplexed. I installed the electric gauge and find it reads more than 20 degrees hotter than the manual did.

I noticed in the directions it said not to use teflon tape or sealant on the threads. The fittings are brass and the sensor does not protrude out of the fitting into the coolant. I'm wondering if the sensor is picking up a lot of heat from the block, and registering a false reading.

 

A temperature gauge pick up should be installed at the hottest point of the cooling system. There should be a location for the temp sensor at the top of the engine near where the coolant hose comes out of the engine and goes toward the top of the radiator.
What kind of engine are we talking about?

 

I would think that the hottest place in the cooling system would be at the rear of the block?

 

Coolant flow is from the bottom of the radiator into the block. Flow is through the block up into the heads where all the fire is going on and things are heating up. The coolant flows up through the block, through the heads and in most cases into the intake manifold where most temp sensors are placed. The thermostat is placed at in this area to insure the block and coolant warms. Once warm, the thermostat opens and allows the coolant to flow up into the radiator where it is cooled as it flows toward the bottom of the radiator.
If you are putting the temp sensor in the block you are getting water that has been cooled by the radiator. Your temp gauges are being burned up by exhaust temps is my guess. Those block holes are for draining the coolant.

 

Well said. Thanks for explaining that. It is always good to learn something.

 

After having the sender in the thermo housing for a couple of days, I can see that yes, the reading is hotter than when I had the mechanical sender in the block. So, what the reading is coming off is the heated coolant that is being pumped out of the engine. It is not the temp of the engine, but of the heated coolant being put in the radiator. By the time the thermo opens and allows new coolant in, dropping the temp in the engine, I am reading the temp of the coolant that is no longer in the engine.

Maybe that is want you want to read, but I prefer to know the temp in the engine itself. I am going to go back to the mechanical gauge, and I'm going to install the sensor in the block.

Thanks for your help.

 

Does the gauge ever read hot? If not it is either the sending unit or the gauge or the printed circuit board. To see if the gauge works you need to test it by seeing what it reads with different resistances inline with gauge. According to Ford specs, 10 ohms in line with the gauge should read Hot, while 78 ohms in line with the gauge should read Cold. If the guage reads right with these resistances, then the sending unit is likely the problem.

 

It never reads Hot I'll try those out and see it it helps, thanks

 

The thermo doesn't allow coolant IN the engine it allows it OUT. That is the reading you want right before the coolant leaves the engine and goes into the radiator to be cooled down. That is why all the instructions for electric fan controllers (that use probes in the fins) say the probe should be mounted in the radiator fins close to the inlet at the top. That way the hottest coolant from the engine is flowing right around it.

EDIT: I misread your post above sorry. I see now what your talking about. Sorry.

But why would you not want to know the temp of the hot coolant right before it leaves the engine?

LETS SEE HOW MANY TIMES I CAN EDIT 1 POST:

You're still measuring the coolant temp just in a different spot where it is cooler.