Recently, I bought a new set of electrical AutoMeter AutoGage type aftermarket gauges to add to my 66 Coronet with the /6. I want to be able to use both the stock in dash temperature gauge and the new below dash AutoMeter temperature gauge. Here is a picture of my installation with the two senders in a tee and then into the head. The stock in dash gauge sensor is on the left and the new AutoMeter sensor is on the right.

I tried to be careful and eliminate a big air pocket by putting coolant into the high side (right side) of the tee fitting just before putting the new sensor in.

Alas, so far neither gauge is getting warmer than about 125 degrees after two or three driving cycles. Will this tee set up ever work to give proper water temperatures or are the sensors just too far away from the head? The stock in dash gauge was working fine before this and I tried the new gauge sensor alone in the head port and it worked fine showing about 165 degrees after the thermostat opened.

If this won't work, I will sacrifice the stock gauge and just go with the new gauge.

Thanks for your input!

Jon

Well, you are isolating the senders from the heat with that long tee and fittings, so that is probably why they are not heating up. The later Slant 6 heads had 2 (or even 3?) temp gauge/sender holes, if you wanted to get a different head. Or, you can get a 1.5" tee with a sender fitting for your upper rad hose, and that will read pretty close to the factory location (once the thermostat opens). The easy option is just run the aftermarket sender into the stock location and forget the factory gauge...

Sounds like a cool car!

Lou

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I had to do similar on my 01 Durango with its 360 magnum. with the "beer barrel" intake the only way I could run the aftermarket gauge was to pull the nipple from the intake for the heater hose and put the tee there. It works fine, still have great heat but I think the accuracy might be a little off as a result of the "stand off". It rarely reads over 180 even though I know its running a bit warmer.... If the outside temp is over 90 itll occasionally read a bit more. It always does for a minute until water gets moving again when I shut it down....
as has been said above the head on my /6 in my D150, has a couple of additional passages in the head besides where the original sending unit next to that. Mine has a 77-78 "peanut plug" head. I dont have the original head from that engine no more (74 engine) but I believe it too had at least 1 more passage in the water jacket next to the factory sending unit hole, with a pipe plug blocking it off.

I did try a smaller (1/8" NPT) Tee without the reducer bushings you see here to get everything closer to the head BUT the two sensors are too long and run into each other inside the 1/8" Tee. So I had to try this 1/4" NPT Tee and the reducer bushings.

I probably won't change the head for this but if/when a rebuild comes around, I could get a later head. I wish my head had more than one port. Thanks for that tip!

Also, I think I'll leave the hoses alone for now but might come back to that later. Wouldn't a heater hose be hotter (more representative) than the upper radiator hose which is returning cooler water to the head? A good option to consider.

For now, I'll just remove this plumbing and use the AutoMeter sender in the head port.

Thank you!

Jon

another option instead of replacing the head with a later head would be to replace the radiator with a later radiator. I have a volare radiator in my 65 and it has a port on the tank for the factory vacuum valves that were used in the late 70's

Drain a quart of antifreeze out, remove the thermostat housing, drill and tap a second 1/8" hole in the head. Done it several times myself.

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Rick's got a good solution there too. The upper rad hose is about the hottest place there is coolant, since that is where the hot water exits the head to go to the radiator. It should be VERY close in temp to the head sensor location, once the thermostat opens. Heater hoses will be substantially cooler, especially when the heater is off (coolant flow valve closed), but even when open.

Lou

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Thanks for all the suggestions. I appreciate your expertise and will keep it in mind.

…a 1/8" pipe thread hole in the bowl portion of the thermostat housing, and install your sender there. Nice thing about doing it this way is you get to "see" the thermostat open.

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I finally am getting back to this. I'd like to get a spare housing to drill and tap in case I screw it up! Is the proper housing replacement the Dorman 902-3015? I see it at NAPA for about $12. Thanks.

Pretty much anywhere in the water jacket, once the engine is warmed up, the temp of the coolant should normalize and be pretty consistent.
And putting the pickup for the aftermarket temp gauge in a tee a little ways from the head.... It might take more than a couple of trips to town to burp the air out when it's "above grade" but it eventually will. Then only way I know to "speed that up" would be to put a cross in instead of a tee, with a pipe plug in the highest leg that faces up and use it as a "bleeder" once the thermostat opens .. you won't have to completely remove the plug if you loosen it a turn or 2 should be enough, as you loosen it you should see air escaping and eventually fluid... Even at the high point on the head it should still be below the top tank of the radiator, so gravity should help bleed the air out. Then tighten the plug once bled out

Thank you. When I had the tee installed I had made sure it was full of fluid as I inserted the second (higher) sensor. I drove it many trips, many cycles and neither sensor ever got above about 125 degrees. It seems the tee is just too far away from the flowing fluid and effectively only measures the head surface temp. I removed the tee. Now I'm going to locate the second sensor in the thermostat housing as suggested above. Then I will have a sensor on either side of the thermostat and will see how/when it opens. Just a fun little project since I need to replace the antifreeze anyway and I want to put in a new 180 thermostat at the same time.

Before ordering another housing from NAPA I was hoping one of you folks could verify that the Dorman 902-3015 sold by NAPA is the right housing.

I drilled and tapped the new thermostat housing I got from O'Reilly. Now I'm ready to switch it out for the current housing when I change the coolant and thermostat. Thanks for the suggestion! In the pictures is the stock temperature gauge sensor. I will move it back to the head and put my new AutoMeter gauge sensor into this new housing.

Jon

I finally got done with this job. I was waiting for a non-busy day with nice weather to work outside. See the pics. New thermostat housing with aftermarket temp gauge installed. I also switched out the thermostat 180 for the 160 that was there and replaced the coolant. Both gauges work fine, one on either side of the thermostat. Thanks all for the suggestions.

Jon

Glad it worked out.
Just personal preference here but I've had better luck with the mechanical type gauges than the electric over the years.