[dv657172]

Question originally posted on Heating & Cooling section but no replies

100% drag car
68 Pontiac 400 block with #16 heads

Looking for good spot to install a temp sending unit in the block or heads to signal fan and water pump to come on

Originally I installed manual switches so I can continue to run them even after car is shut off (car originally raced in South FL). Would like to have them also come on automatically so I dont forget to turn them on. Have the wiring figured out I think to run them both ways, just need a spot for the sending unit

Have a Torker II intake manifold with front DS fitting at water crossover used for under dash temp guage

Griffin radiator with only fitting at bottom DS used for drain

Thanks for any ideas

[chuckies76ta]

The water cross over is a good place for sensing temperature in my opinion. I have a Temperature gauge on our 505 cu in IA2 with a sensor in the coolant cross over and also the sensor for the fans in the water cross over. My sensor is rated to turn the fans on at 185* and shut of at 175* and I can watch the temp gauge to confirm temperature. I also kept the water pump bypass in operation. I also bypassed the heater core and kept the return in operation.

You want your system for the water pump and fans to be fail safe. By that I mean if you forget to turn either one on, you don't end up in a bad situation. Having said that you want the water pump to turn on a soon as the engine is started an stays on till engine is shut off. You also want to install a manual by pass switch to start/stop the water pump with or without engine running.

On the fans you want to have them come on automatically if you forget to turn them on. This can be done with a sensor in the water cross-over. You also want to be able to manually stop/start the fans with or without the engine running.

[steve25]

The best place to put it is where it was moved to in the low compression heads, that being as in here in this photo.

Here in this location it senses head water temp more then block water temp as in the factory water crossover at the front of the intake.

I have done this on early heads and there’s plenty of meat there to do it even without the boss being there.
The factory hole / sender is 1/2” pipe thread so the drill and tap to do such is not cheap.

If your aftermarket temp gauge uses a 1/8” pipe sender then it’s a breeze to do this mod.

If you need to go 1/2” pipe and do not have a big ass electric drill to power that size drill bit ( 3/4” ) then you might want a machine shop to do the job for you.

[dv657172]

Steve - any good place to put it without removing a head?

Chuck - I have my guage sending unit in the water crossover and only one fitting there. Do you have two fittings?

[Dave Polichena]

If it is 1/8 pipe, you could drill another hole in the water crossover if there is enough meat. You could weld a bung to it if it is too thin.

[chuckies76ta]

Originally Posted by dv657172

Steve - any good place to put it without removing a head?

Chuck - I have my guage sending unit in the water crossover and only one fitting there. Do you have two fittings?

Yes I have two places to install fittings. You don't want to remove the head just for a coolant fitting. The thermostat still dictates the temp of the engine as far as when it opens. You can always separate your water cross over from the intake and have it drilled and tapped for a port. Just remember it's NPT.
OR buy a cross over with two ports.

[chuckies76ta]

The left sensor is my gauge in car and the right one is my sensor for the fans. https://www.summitracing.com/parts/s...17?seid=srese1 The way these sensors are wired is a path through the stak-on to ground.

Butler cross over. https://butlerperformance.com/i-3015...ml%3Fq%3Dwater

Kauffman also. https://www.krepower.com/Pontiac%20Intakes.htm

[firechickenman]

Mine is set up like Chuck's. If I were you, I would put on a dual port crossover. I have a Flex-A-Lite controller which automatically turns the fan on. I can also override it to turn it on or off as needed. I believe this is the one I have: https://flex-a-lite.com/variable-spe...re-sensor.html

[Skip Fix]

I have seen an extra aluminum fitting you can put in the radiator hose, cut the hose and a clamp on either side.

[dv657172]

Thanks for all the replies guys, really appreciate the feedback. Think I will set it up like ChuckiesTA