temp sending unit?
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Freshman User
Joined: Oct 2005
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From: carova beach(OBX)
temp sending unit?
I was wondering if anyone can tell me where to mount a aftermarket temp guage(capilary bulb) on my edelbrock intake or block? Im not sure if the origonal intake had a sending unit on it or if i just cant find it on the block. I have a 1980 F-250 4x4 351m.
Senior User
Joined: Jan 2004
Posts: 131
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From: Midwest
I recent put an edelbrock 4 bbl. intake on my 351M and it had a plug in the intake for an auxilary gauge. Coolant does flow through mine, had the plug out and tried to start the engine and coolant went everywhere. The plug on the intake is before the thermostat, so the gauge will show hotter than your OEM gauge until the thermostats open up.
Posting Guru
Joined: Dec 2002
Posts: 2,003
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From: chicago burbs
1979ford, if you have coolant in your intake then you don't have an M, turn your M upside down (W) and you'll be all set. there is no mistake anyone can make that will get coolant into a 335 series intake manifold, there is NO passage in the intake or from the heads. what model number is your intake?
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Freshman User
Joined: Oct 2005
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From: carova beach(OBX)
I noticed a spot just before the thermostat where an old emissions thing(or somthing?) was and pluged it in there. I also see why the guage may read a little hotter b/c its before the thermostat, but my guage is reading between 220-240. i do think the thermostat is working b/c it will get to about 240 and the drop back down to 220-230 range. but im not sure if that is a normal temp reading. I know it should be around 190-210 or so but it seems to be a little high to me, What do you guys think? circulation seems to be good to.
More Turbo
Joined: Aug 2004
Posts: 689
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From: Rodeo, Ca.
Change the thermostat, that reading is too high. Also, GRClark is correct, no water in a Cleveland or M engine, only vacuum ports. You want the temp. sender before the thermostat anyway, that way it reads engine temp. until thermostat opens.
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Cross-Country
Joined: Sep 2019
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Tagging a question to this thread about the 351m temp sending unit - the location is on the block, just under the tstat and water neck. I'm having trouble getting a sensor to thread it! I can screw in a 5/8-18 bolt in freely, but I believe this is an NPT threaded hole? Now - the real problem - I've tried two from Oreilly's and they don't fit! Too big - the OD looks just barely bigger than my 5/8" bolt OD, and I can't a even a half turn into the block. The pitch still measures 18TPI, but it is...not perfect...I can see a little light on my thread gauge, but it's the best fitting one.
Anybody have trouble getting the temp sending unit screwed into the block?
Anybody have trouble getting the temp sending unit screwed into the block?
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Joined: May 2015
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From: Tri Cities, TN
That should be 3/8-18 NPT. If the sensor you have won't start in there you may need to run a 3/8-18 pipe tap in there and clean up the threads. Or if you can't come up with a tap, try a small stiff wire brush.
Cross-Country
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Thanks! I picked up a 3/8" NPT tap, and could spin it into the hole with my fingers - so that's confirmed. Not sure why the actual temp sensor wouldn't go it. I even had pulled off the factory/china applied teflon to make sure it wasn't too thick...When I put a wrench on it, I started shaving brass of the sensor. Hmm.. I'll try again.
Meanwhile I looked at pictures from before the rebuild, and it looks like this hole in the block just below the tstat and water neck was plugged in my old block - is there someplace else this sending unit could've gone? I have the original waterneck, and that has both plugs, so it wasn't there.... When I brought my block to the machine shop, they swapped it out b/c it was already bored 0.060" over, so I lost the hard evidence.
Meanwhile I looked at pictures from before the rebuild, and it looks like this hole in the block just below the tstat and water neck was plugged in my old block - is there someplace else this sending unit could've gone? I have the original waterneck, and that has both plugs, so it wasn't there.... When I brought my block to the machine shop, they swapped it out b/c it was already bored 0.060" over, so I lost the hard evidence.
Logistics Pro
Joined: May 2015
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From: Tri Cities, TN
Since a pipe tap is tapered there should be a point where it stops turning easily and starts to cut. Try a short 3/8 pipe nipple to see if it goes in like it should. Try a sensor from a different source. Don't know what's up there it should go right in. I suppose you could put it in the water pump if yours has a plug that isn't being used. If you put it in the thermostat housing it won't read correctly until the thermostat opens.
