Customs Which temp sender location to use?

I'm converting over to a dual fan aluminum radiator set up on a 350 sbc. It has two different temperature senders , one in the intake manifold near the radiator thermostat location and one in the side of the block under the drivers side exhaust manifold (headers) outlet.
Which location should I use for the electric fans ?

 

the location in the radiator

 

Of the two engine mount locations, I think the intake manifold near the thermostat housing will give the most accurate reading regarding the need to lower water temperature.

 

Just my sometimes incoherent rambling, but it seems to me the temp sender in the intake or head should be for the dash gauge. The fan pulls air through the radiator. The fan needs to run when the coolant in the radiator is hot. So seems logical to me the fan switch sensor should be in radiator. As Squirrel said.

 

Put your sender in the intake the head runs 15 to 20 degrees hotter than the intake manifold. The temp at the thermostat is the true temp of the engine.

 

Agreed, but the OP asked about block or intake. Perhaps there isn't a location in the radiator.

 

I have one of the tube insert into radiator sending units as well, but somehow hate them! Anyway, thanks for the info guys! The spal tech advised to put it on the one near the thermostat housing.

 

This does bring up another question. Should the dash temp gauge wire run from the sending unit in the side of the head or from the one near thermostat housing? The one on this motor runs from the one on the head.

 

The one in the head will always show a higher temp. For the fan, use a 180 sensor in the rads bottom tank, use a temp gauge sender in the intake manifold.

 

One of my off topic hot rods has the sender in the head. When the engine is cold, before the thermostat opens, it will go almost to the top of the operating range. Then when the thermostat opens it will drop back to normal. Yes, the thermostat is good. I have always assumed this is because the coolant in the head heats up faster simply because that's where most of the heat is transferring to the coolant from the exhaust. It's not really a problem but it can freak you out a little if you're not expecting it. Someday when I get ambitious (yeh, that'll happen) I'll move the sender to the intake.

 

I see no issue running the sensor in a head? Yes it will call the fan on sooner, but why is that a problem? Since there's one port on each head with a SBC you can have a sensor for the gauge and one for the fan in each head. That's what I use to call my fan on and my engine stays under 185 degrees all year round.

 

I had an issue with the port in a manifold reading hotter than it should. I think there was a pocket that allowed the manifold to trap air in that area. The gauge would show the engine as overheating and it was fine. I moved the gauge to the cylinder head and it reads fine.

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I've always found drilling an 1/8" hole in the too of the thermostat to allow some flow all the time and to bleed air to keep the engine at a more steady temp. Most 1980s and later engines have a brass jiggler to purge air.

All the vehicles I do this to are only driven in the summer so sub zero temps wont matter.

I've always had the best results with putting fan switch/sender in the lower radiator tank. I've used the drain tapping in most cases. I like an adjustable sensor which fires relays for high and low speeds which is easy for a two fan setup.

Basically low setting commences the two fans in series for nice quiet cooling, and high connects them in parallel for full 12 volts for the most airflow. That's what I did with my dual Spals.

 

Each SBC head has a hole in it, can run a gauge in one head and the fan switch in the other. Both should jive with each other that way.

Be under and between 1 and 3 on the driver side, 5 and 7 on the pass side