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I just built a new engine for my 72. Its a 358 ci with a 10.2:1 compression and I'm using Blueprint Engines aluminum heads. The problem is the water temp sensor is too big to fit in the head. The od thread size of the sensor is 13/16" and the head is 5/8" od. Is there another sensor I can use or does anyone have any ideas how to make this work?
Also, I'm thinking of running AC R43XLS spark plugs. Do you think this a good heat range? I'm running a roller cam with .502 intake lift, .510 exhaust lift.
IIRC, Willcox has a fix for your temp sensor. The 43 heat range plugs are close. You need to keep an eye on what the plugs look like anyway. The head manufacturer should be able to give you an idea of where to start with on heat range.
Is the engine in the car? are the heads fitted? the easiest way would be to tap out the hole to fit the sensor. If you do a search you will also find reference to machining down the sensor and rethreading it, this is what I did to my '70 when I fitted Dart heads, if I had noticed that it wasn't going to fit I think I would have tapped the hole out but I had already fitted the heads and the engine was in the car.
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Is there a tapped/plugged hole in your intake manifold near the thermostat opening? Put the sensor there. If not, drill and tap a hole in that vicinity. It might be an easier fix or just buy another sensor with the smaller diameter thread.
I too had that same issue with the water temp sending unit. I believe that 5/8" OD is actually a 1/2" NPT, maybe? I took the head to a machine shop. I wanted to keep the GM sender. Shop charged me $30 to drill & tap for the sender. So I guess its a toss up. Buy new sender or pay machinist.
If you decide on farming out the work, take some painters tape and cover the entire facing of the head and the intake ports to protect it from accidental scratches at the machine shop.
Your aluminum heads likely require a longer reach sparkplug. Usually it takes a 3/4" reach. When selecting plugs, not all companies are on the same page as far as heat range. On a scale from one to ten, one companies cold plug is 1. Another company it might be 10 the coldest.
At this point I don't want to machine the head because the motor is installed. Even though I'm in the middle of a frame-off and access is very easy I don't want to go backwards. I should have addressed the problem before finishing the build. The best options are to find a smaller sensor or move the sensor to the intake which I'd rather not since it wouldn't look right up there to me.
76 stroker, I almost said 3/8 NPT but it seemed awfully small. I get confused on those NPT stuff.
Nice build cabman. Very unusual engine paint color. Works well with aluminum, blacks & grays.
Update add:
Watch those chrome water-necks. They can be a son of a gun to seal. After four attempts, three weeping, I ended up using a $25 silicone gasket and a dab of waterneck / waterpump RTV gasket sealer made by Permatex. Its glycol proof where as most RTV is not. Found the small tube of it at AutoZone.
Last edited by HeadsU.P.; Nov 13, 2018 at 07:19 PM.
Thanks, my car color will be Daytona Sunset Orange, so the engine will blend in nicely. I will have the headers coated and I was thinking of silver, but I'm kinda liking the black.
I have those same heads and my coolant temp sensor fit fine. I am trying to find which one and unfortunately I can't because I have dozens of Summit orders and not sure which one it was on. If I find it I will let you know.
Thanks, my car color will be Daytona Sunset Orange, so the engine will blend in nicely. I will have the headers coated and I was thinking of silver, but I'm kinda liking the black.
Me too, especially your "satin" black. Much cooler than flat black. Silver color might be too much.
Is that a ceramic engine paint? That stuff from Eastwood is very impressive for durability. I applied it with a brush years ago. Still looks new.
Last edited by HeadsU.P.; Nov 13, 2018 at 12:48 PM.
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NPT uses the inside diameter of the pipe, so a 1/2" npt's threads may be 5/8" and 5/8 is about 3/4" but you can not use regular taps as NPT's are tapered.
I am running blueprint aluminum heads 538 roller cam on my small block chevy also. I had my local machine shop turn down the old sensor and rethread to the correct size. now screws right in the blueprint head no adaptors. Blueprint Recommended spark plugs are Champion 792 with .045"" gap and that's what im am running in my engine with 6000 trouble free miles. hope this helps
Last edited by jpattt24; Nov 14, 2018 at 01:11 PM.
I suggest you contact Willcox and get their adjustable resistor. It is about a wonderful contraption. I put up with an inaccurate temp gauge on mine for decades and it was fixed so easily. While you're at it - you might as well buy the temp sender Willcox recommends for the 3/8" head hole. Here is my story. I am so glad that I did it. https://www.corvetteforum.com/forums...post1593978953
Originally Posted by cabman72
I just built a new engine for my 72. Its a 358 ci with a 10.2:1 compression and I'm using Blueprint Engines aluminum heads. The problem is the water temp sensor is too big to fit in the head. The od thread size of the sensor is 13/16" and the head is 5/8" od. Is there another sensor I can use or does anyone have any ideas how to make this work?
Also, I'm thinking of running AC R43XLS spark plugs. Do you think this a good heat range? I'm running a roller cam with .502 intake lift, .510 exhaust lift.
p/n 6400759A. I know it costs a few $$ but by the time I pulled a head and tapped it, or relocated to intake, it was worth it to buy this part (there was a short lead-time) and throw some sealer on and screw it in. I suspected it wasn't reading correctly early on, but believe I have confirmed it's fine after checking my motor with an infrared thermometer -- everything is new and fortunately runs very cool.
I just built a new engine for my 72. Its a 358 ci with a 10.2:1 compression and I'm using Blueprint Engines aluminum heads. The problem is the water temp sensor is too big to fit in the head. The od thread size of the sensor is 13/16" and the head is 5/8" od. Is there another sensor I can use or does anyone have any ideas how to make this work?
Also, I'm thinking of running AC R43XLS spark plugs. Do you think this a good heat range? I'm running a roller cam with .502 intake lift, .510 exhaust lift.
Thanks for any help you can give me.
Mike.
If you have a full Blueprint engine, they will specify the best plugs for it that they dyno'd it with. I went with their recommendation.
Is there a tapped/plugged hole in your intake manifold near the thermostat opening? Put the sensor there. If not, drill and tap a hole in that vicinity. It might be an easier fix or just buy another sensor with the smaller diameter thread.
That's what I did when I installed my ZZ4. It does run about 10 to 15 degrees cooler there proven by a stick on thermocouple and also an IR heat gun. I used both to check the temp at the head location and the intake location and I used both to verify that the temp was correct. Just have to keep that in mind when looking at the gauge.
The best options are to find a smaller sensor or move the sensor to the intake which I'd rather not since it wouldn't look right up there to me.
You won't even see it as the upper radiator hose will be covering it. The one problem that I'd see is the connector. The original connector for my '71 is the slip on type that goes on from the side over a the round button on the sensor. If yours has the blade type connection then it won't work at the intake location as there is no room for that type of connection.
Water temp sensor
