Temperature sensor position.

Frans

1000+ Posts
I went to visit my son yesterday and we got busy on the Caravelle. He bought some new stainless steel bumpers for the Caravelle and they are beautiful. Fitting was easy and very little adjustment was needed. The whole set cost him about $1200 which is about the price of chroming one only. You can see the quality in the photos and it is polished stainless. Can last a lifetime.

I was fiddling in the engine compartment to remove a gauge cluster that didn't look good. In the process, I was looking for the temp sensor and couldn't find it at first. Nowhere in the water. Then I traced the cable and it came out to an aluminium block bolted to the head at the same spot the temp light switch is normally mounted. What the previous owner has done is to make a little solid aluminium block, drill and tap it, and screwed the sensor that normally goes into the water somewhere into this block and mounted it on the head. It screws into a blind hole, with no open ends.

The gauge worked fine when we drove it up from Wellington but now I'm wondering what do you think the accuracy will be in doing it this way. Will it be accurate or if not will it read high or low?

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Bustamif

Member
I believe the sensor should be in contact with the coolant to give an accurate reading of coolant temp, same as an oil temp sensor should be in contact with the oil.
I know of situations where coolant has leaked out or boiled off but the gauge says everything is fine, because the sensor is not in contact with any coolant.
 

85Fuego

Member
I believe the sensor should be in contact with the coolant to give an accurate reading of coolant temp, same as an oil temp sensor should be in contact with the oil.
I know of situations where coolant has leaked out or boiled off but the gauge says everything is fine, because the sensor is not in contact with any coolant.
Agree - you're reading block temp
 
On the Ventoux head it is pretty easy to make up a plate replacing the thin plate on the back of the head and thread it (NPT, I think) and insert sensor here so it is in contact with coolant just near cylinder 4. Need either pipe/aviation grade loctite or plumber's tape to make good seal.

Have done this on Reg(4CV), who is the poverty pack model without temp gauge and it works well

Can see the aluminium block trick working OK in steady state, but what I want in temp gauge/warning light is something which tells me quickly when I've lost water and am about to destroy the engine. Suspect that the Aluminium block one would ensure a timely invitation to the funeral, but wouldn't give you the opportunity to do much to prevent it.

Andrew
 

schlitzaugen

1000+ Posts
I think it depends on the kind of sensor you're using. Some sensors are meant to read the temperature off the coolant, but there are also sensors meant to read the temperature off a metal body. All the OEM sensors I have seen in cars were meant to read coolant. These don't read well when not immersed in coolant hence no use when coolant level drops. That would suggest it is better to read the temperature off the head metal but I guess you need to choose carefully where you place the sensor. Your gauge might have to be recalibrated too if using a non OEM sensor.
 

rubyalpine

New member
I agree with Bustamif, you need to know the coolant {not the alloy head} temp.
The R12 motor has a cast allloy plate on the end of the cylinder head, already threaded for the temp sender unit. It just needs a brass reducing bush to suit the sender unit.

Henry
 

Fireblade

Member
That head temp sensor was relatively common in the '70's and the quickest way to get a temp gauge into an R10. While not ideal - it was better than the factory arrangement - where the temp light shares the wiring with the oil pressure light. Despite not being immersed in coolant, it actually works quite well - firstly letting you know if your thermostat is working (the more common cooling system fault) and second - giving plenty of warning if things were getting abnormally hot - there is a bit of room between 80 (normal running temperature) and 100+ (when things start to go really nasty). The factory light simply announces "congratulations, you've cooked your head" - and you can guess how I know this!
 
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simca1100

Member
I'm no expert on these cars but I have vague memories of it being fairly common on R10s to have a head temp sensor fitted as an aftermarket extra. As a youngster I used to work at a car auction that had an old feller there who was into R10s and used to tell me stories about them. He told me about fitting a head (metal) temp sensor to them, as in his words they were "easy to cook."
 
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