Should the Coolant Temp Sensor really be located @ the H2Opump?

In the admittedly unlikely event that coolant somehow stops circulating through the system, the reported temp at the pump becomes less and less accurate/useful as the head temp gauge becomes moreso … yet the Coolant Temp Sensor is located in the H2Opump. With the CTS where it is, the head temp can easily exceed 239°F, while the H2Opump temp can stay under 212°F.

It would be a very minor miracle that I'd be proud of if I just got anyone else to seriously consider doing what I'm about to do …
Can anyone think of a reason NOT to relocate the Coolant Temp Sensor to the head between cylinders 1 & 3? (Doubt it'd reach all the way to cylinders 6 & 8.)

what type vehicle do you have ,size engine. the sensor at the air pump would be air temp not coolent temp unless it is in coolent.

depends on the engine. on a GM 60degreev6, you'll have it in one of two locations, one is right under the thermostat(which is about as far down the coolant path as possible), the other is at the end of the head near the thermostat(also pretty far down the path).

your sensor/guage will certainly read differently if you were to relocate it like that.

Maybe it depends on the engine, but I'd think your concerns is probably exaggerated. Maybe you have the sensor in the wrong location? It should be in the coolant path to read coolant returning from the engine before the thermostat. For most older V8's, this means either in a head or in the intake coolant crossover going to the thermostat housing.

I have a LT1 with CTS in the pump (in a location that does measures hot coolant from the engine) and gauge sensor in the head and the gauge reads ~180* just like the thermostat opening point and very similar to what the PCM is reading. I'd think most V8"s would react similar with one sensor in the head and the other in the intake coolant crossover going to the thermostat.

95 Chevy Caprice 9C1-LT1 5.7L V8. [This thread was tagged with LT1 & $ee.]
Have not mentioned the AIRpump; utterly irrelevant to this discussion [nevermind disabled per the final OEM .bin].
The COOLANT Temp Sensor [that ONLY reports to the pcm] is located where GM originally intended for all LT1 cars, in the H2Opump [and the H2Opump has the thermostat on top of it].
The Head Temp Sender [that ONLY reports to the instrument panel] is located where GM originally intended for B- and Y-LT1s, in the passenger-side head between cylinders 6 & 8.
[In F-cars, it's in the driver-side head between cylinders 1 & 3.]

The LT1 engine family is reverse-cooled and has no internal coolant crossover in the intake manifold.

The difference between the coolant temp at the head and at the pump can be considerable even when coolant is moving as intended.
Scott Mueller noticed this in 200x; http://forum.theherd.com/topic.asp?TOPIC_ID=110.

What concerns me is when the coolant is NOT moving as intended.
Specifically, the temp reported at the head sender WILL DEFINITELY warn of impending overheating, whereas the pcm will likely never find out in time to do anything about it because, for whatever reason, the pump is no longer flowing coolant, so its temp climbs much more slowly than the head temp.

In that Scott Mueller article, he suggests relocating the head temp sender to the H2Opump so that the IP and the pcm get identical readings. In the event of impending overheating, this could suddenly become a regret.

I propose relocating the Coolant Temp Sensor from the H2Opump to the driver-side head.
[On F-cars, the Coolant Temp Sensor and the head temp sender would be one and the same on the driver-side; on B- and Y-cars, the head temp sender would remain separate.]
Among other things, in the event of impending overheating, the driver still gets warned as soon as possible, plus the pcm ALSO gets 'warned'.
Even without the LT1's HiTemp Enrichment, several tables could be written so that the engine behaves very differently once it exceeds, say, 221°F.
[Manual transmission cars, for example, tend to disable 'skip shift' entirely; I vehemently suggest setting the enable temp to 221°F.]

I'm on my 5th LT1 B-car, all of which only exceeded 217°F [at the H2Opump] because they were about to overheat for some reason or another.
However, had the Coolant Temp Sensor been installed [by GM, or anyone else] in the head …

Can anyone think of a reason NOT to relocate the Coolant Temp Sensor to the head between cylinders 1 & 3? Specifically, I don't see how it would adversely affect normal operations.

If your coolant stops flowing, I don't think the CTS location is as important as the position of the gauge sender. The only remedy to this problem is for you to turn the key off. Nothing your PCM can do will keep the engine from melting down if you keep it running without coolant flow. The water pump probably isn't the best location for a CTS, but it seems to have worked for GM in this application. It wouldn't hurt anything to move it into the head, though.

What's the PCM really going to do? As far as I know, a LT1 has no over temperature protection like cylinder shut-down that some newer engines have. There are some little things like you mentioned but that's the extent of what it can do. You need the gauge to read the hot temperature so you can shut-down the engine. A bunch of worry about nothing. It's not very likely that the direct drive water pump in a LT1 would quit pumping coolant anyways.

221*F isn't hot in a LT1. The LT1's with electric fans didn't have the fans come on until 219*F.

He seems to be claiming the gauge would read 120* when highway driving on a cool day. I've driven my car on cool days and I've never seen a low gauge reading of any significance. I have a Dakota Digital cluster with an accurate gauge and digital temperature readout.

I agree with Lionelhutz and mostly with fastacton.

Leave the CTS in the water pump, because the tune has been made for that temperature reporting location. This location will get an average of what the engine is actually at and under those conditions is what the tune has been set for. Moving sensors around like this can cause problems, because the PCM may think the engine is actually running hotter than what it's tuned for at those operating conditions.

If the water ceases to flow through the engine the temp reported at the cylinder head or the water pump to the PCM is not going to make one iota of difference in being able to save the engine.

On some systems I've seen some adverse results by placing the sensor in the head as opposed to a coolant crossover, or similar location, especially when the system was tuned with it in that crossover type location.

Also, just because the thread may have been tagged with certain items, does not mean that people will know. it's best to be explicit and mention exactly what the application is in the body of the question.