EFI Guys - Coolant Temp Sensor Location?

The next big project scheduled for the '73, after the front suspension, is the conversion to EFI and distributorless ignition. Building on the info in Chris' EFI thread below, I won't be doing this from a minimalist perspective. I'm including the complete suite of sensors - IAT, TPS, CLT, crank position sensor, knock sensor. (The knock sensor may end up being pulled - there's a lot of clatter in these engines and I don't want false signals screwing with the timing.)

Still some final details to work out, but I've got most of the conversion's physical changes noodled out. The only piece still up in the air is the placement of the coolant temperature sensor. There are a lot of possible locations that I've looked at. Quickest and easiest seems to be to tap a bung into the thermostat cover and measure from there. It's also possible to place a probe into the water stream headed towards the radiator, like with cooling fan thermostats. The problem with both of these is the differential between the coolant temp on either side of the t-stat. (Maybe less of a problem using the t-stat housing due to "leakage" through the t-stat itself...?) The same basic idea works with the heater return line, but in that case the problem is that the only time there's a full-time flow of coolant is if the heater valve is open. Not so nice in summer.

My latest thinking is to fab some sort of t-junction or y-junction that goes into the stock temp sensor location on the head. Both sensors - the dash temperature sensor, and the EFI sensor - would be mounted to this. It seems that the problem here is that by doing that, neither one of the sensors will be in the actual coolant stream.

I'm obviously over-thinking this. What have you guys done in your installations?

Rick,

FWIW the stock ECU temperature sensor location on my V6 conversion is located in the head just prior to the thermostat. The gauge temperature sender is located in the block.

Could you have a spacer machined, tap into that for the sensor, and mount the thermostat on the top of the spacer?

I like the spacer idea, i have seen somepeople drill and tap the thermostat elbow, but you have to make sure it doesn't interfere with the thermostat function

Rick,
The moss solution on the later model heads is to use the head take-off for the water choke. On an earlier head you could tap both a hole here as well as make two holes for threaded studs if you were adventerous and then order from Moss the block that they use for the Coolant temperature sensor.
Frank

rick, is it possible to use the existing temp sender for your ecu to pick up coolant temp?

on a marine motor that i installed EFI on, i "think" i was able to use the same sender for both.....but my memory sucks these days....

I drilled a hole in the head about an inch below the stock sensor and tapped it for the GM sensor. It has worked great for several years and that way you can still have your stock gauge. I did this while the head was on the car and used lots of grease to catch all the chips.

I would imagine that location makes a considerable difference

My old BMW has what amounts to 4 temp sensors on the t-stat housing (plus a couple on the rad and I think another one somewhere else<G>), but they are "before" the t-stat itself, so they measure temp within the engine (at least that part of the engine) rather than on the outside of the stat which would register only once the stat was open.

I suspect that if you looked carefully at other cars you'd see the sensor location is going to be "inside" the stat-controlled zone.

That would make it difficult to put the sensor in the B stat housing since that area is "outside" the controlled zone...no?

Drilling might be the answer, actually, but I need to sleep on it! Sean Brown did a fantastic P&P job on this head a couple of years ago. It'd be a bit of a shame to screw that up. :eyepop:

Rick,
I know for a fact it can be done as Peter Burgess did it on a presmog head...but that is Peter who had a lot more knowledge than me. Perhaps Sean would be willing to do it for you using a smog head as a guide.
Frank