Thermostat spacer

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1994redram

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I ordered a Holley Sniper EFI to put on my magnum based 408. The street demon carb has treated me well but I've had the itch for an EFI conversion for awhile. I'm currently running an Air Gap intake on the engine with all of the factory magnum accessories. The two coolant ports are being used for the heater hose and gauge sender. I need a 3/8 port for the EFI coolant temp sender.

I'm looking to put a thermostat spacer/riser in for a sensor. Mopar thermostats from 1978 and older are all conveniently Chevy sized. 1979 and up mopars use a smaller 'stat and water neck. I could have a bung welded in the intake, however I also have an M1 single plane on the shelf I would like to experiment with eventually. So not having to modify both intakes would be preferred.

Does anyone have a source or part number for a spacer for the smaller thermostat? I think slants also use the smaller size.

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I believe you're correct about them being the same for slants. I'm bored this afternoon, and I've been looking for a spacer for you, but I cant come up with anything. I ended up on a slant forum where someone had the same idea as you, but they couldn't locate the correct spacer either.
One of their solutions was to install an in-line fitting in one of the heater hoses.
Keep looking, or maybe someone else on here can help out.
Good luck, Murph
 
You can put it in the bypass... coolant flows there all the time. The heater hose would not be good as you would need the heater on all the time to get close to proper temp at the sensor.
 
Or you could do what I do;
put a 4psi cap on the rad, and the steam will tell you when it's time to get some ram-air working.
Yeah I'm joking,lol.
But yes, I really do run a 4psi cap and a minimum coolant temp of 205*F. But my system is dead-flat reliable.
 
You can put it in the bypass... coolant flows there all the time. The heater hose would not be good as you would need the heater on all the time to get close to proper temp at the sensor.

There isn't much if any extra room to put it on the bypass with the magnum serpentine setup. The A/C compressor is mounted right above it. The bracket is notched to make room for the hose and clamp.
 
I personally would never put one in line with a hose. You could remove your sending unit and replace it with a T fitting though so you can have 2 sending units. Summit and Jegs both sell the spacers. Maybe they have one and I just missed it. Might be worth checking out.
 
I personally would never put one in line with a hose. You could remove your sending unit and replace it with a T fitting though so you can have 2 sending units. Summit and Jegs both sell the spacers. Maybe they have one and I just missed it. Might be worth checking out.

They have plenty of choices for chevrolets. Those will also work with 1978 and older mopar. But I didn't see one listed for the smaller 1978 and up mopar.

I thought about a T fitting. But I wasn't sure how accurate it would be since there wouldn't be any flow across the sensors.
 
Its possible that Dorman makes a thermostat housing that has a threaded hole in it for magnum engines.
 
I set up a T off of the heater hose on the intake for the thermostat for the electric fan. Seems to work well and you would have flow that way.
 
I set up a T off of the heater hose on the intake for the thermostat for the electric fan. Seems to work well and you would have flow that way.
What is yours installed in?
The OP has a magnum based 408, and I'm betting it doesn't have an electric fan.
Not trying to start an argument, I'm just curious.
 
I'm aware of that. I wouldn't recommend it though. The factory threaded holes have thicker bosses around them for additional strength. While drilling and tapping is easy, its gonna be damn thin, I'll betcha! You gotta be super careful how tight you thread anything in that hole.
 
The only reason I'm into this thread is that I've got a dual plane M1 and I cant thread an aftermarket temp sensor in it. Mine isn't for magnums, but it's kinda the same problem. I'm gonna get the water outlet spacer for mine. It just seems like putting it in-line is a cheesy way to do it. Doesn't look anything like factory installed. Maybe I'm wrong. Can it be made to look good?
 
Let's see what the OP has to say. We've given an option or 2. I think they are all good ideas to make it work. Its about what he really wants in the end.
 
I'm aware of that. I wouldn't recommend it though. The factory threaded holes have thicker bosses around them for additional strength. While drilling and tapping is easy, its gonna be damn thin, I'll betcha! You gotta be super careful how tight you thread anything in that hole.
It's aluminum, just Tig a boss where ever.
 
Anytime I have tried to use a Tee on the intake, the readings become inaccurate as the metal Tee radiates away the heat in the stagnant pocket.
Just put an IR gun on it and watch it. That don't matter for the slow-acting dash gauge, but how are you gonna tune the EFI, when the input from the Tee is 10 or 15 or 20 degrees cooler than the coolant. Good luck with that .
Also, with the temp gauge reading 10 to 15 degrees cooler than what the water is, you may have a false security as to the actual coolant temp. For instance; what if the coolant temp is 230 but your gauge is saying 215? 215 is not too hot for the coolant. But dyno oil starts smoking at about 230 and can be cooking by 240.
The point is, be sure you know what's going on.
And if you are using an electric fan with a 30 or 20 degree temp drop; how is that gonna affect your EFI; IDK, I haven't run those together.
On my car that runs a 205*stat, it might be interesting to watch the thermostat getting a workout, I guess.
 
I do have an electric fan. I "temporarily" wired it two years ago with a relay to run when the key is on. The holley EFI has a built in fan trigger that I'm pretty excited about.

I have thought about just drilling the intake and I have the proper tap and bit. But I'm afraid of it cracking like previously mentioned. Removing it and having a bung welded in might be my best option. I would also need one welded on my M1 intake if I ever switch to that.

Putting it in a T or putting in inline on a heater hose probably wouldn't work too well for the sensitive EFI computer.

It seems like a thermostat riser isn't available for my application. That would have been the easiest and most reliable way. I talked to a local shop that quoted $200-250 to machine one. Looks like I'll go to plan B.
 
I'm aware of that. I wouldn't recommend it though. The factory threaded holes have thicker bosses around them for additional strength. While drilling and tapping is easy, its gonna be damn thin, I'll betcha! You gotta be super careful how tight you thread anything in that hole.

Would be no big deal to have a boss type washer heli-acrced to the water pump, and/or , just make a spacer out of 1'' alum. ,I made one for a 406sbc once for return cooling lines from the rear of the heads , no biggee.
 
How about if you drill & tap in the manifold at the flange covering the coolant passage at the rear of one of the heads? The flange there should be thick enough.
 
How about if you drill & tap in the manifold at the flange covering the coolant passage at the rear of one of the heads? The flange there should be thick enough.

I didn't even think about that. That's a good idea! I wonder how accurate it would be?
 
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