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Hello my friends.
Can anyone tell me what this hole is on the exhaust side of my AFR 195 Enforcers
I had my daughter's boyfriend 'helping' to put the spark plugs in. He said he knew how until he asked me why it was loose! He was trying to put the plug in this hole! Bless his heart.But... When I looked at the plug it no longer had that crush washer on it. Do you think that washer would possibly fit in there and came off? I mean they don't come off easy to begin with and I am not 100% sure it was there before. Just scared to death I'm gonna have to tear down the damn engine again.
Last edited by JohnnyStingray; Jun 13, 2026 at 09:23 PM.
Coolant temperature sender hole. Should be 3/8” NPT.
Great thanks. I had my daughter's boyfriend 'helping' to put the spark plugs in. He said he knew how until he asked me why it was loose! He was trying to put the plug in this hole! Bless his heart.
But... When I looked at the plug it no longer had that crush washer on it. Do you think that washer would possibly fit in there and came off? I mean they don't come off easy to begin with and I am not 100% sure it was there before. Just scared to death I'm gonna have to tear down the damn engine again.
Possibly. You could see if they’re magnetic then try fishing in there with a magnet.
Worst case scenario it could end up in the cooling system, where it could meet the water pump. Not good. If you end up using that hole for the temperature sender remember there’s one on the other head that needs to be plugged.
Last edited by Piersonpie; Jun 14, 2026 at 12:41 PM.
THAT hole appears to be for a threaded coolant plug OR threaded coolant temperature sender for gage. Hole should have Tapered Pipe Thread and there should be be NO washer at all. Did you acquire heads "NEW" ?
Pour a gallon of water into you water neck and some should quickly run out of that hole. RUN, Get a different helper.
Chevrolet water pumps don't have turbines; they do have impellers.
I seriously doubt any spark plug's crush washer fell thru THAT hole, it went somewhere else. into someone's shoe etc.
Last edited by Rebelyell; Jun 14, 2026 at 07:52 AM.
Do you think that washer would possibly fit in there and came off?
Simple test to answer that question is to take a crush washer tie a bit of string on it and see if it fits in the hole. If it doesn't go all the way in (the threads are tapered) then you're good to go and start looking on the shop floor for the crush ring.
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A crush washer wouldnt go in that hole, through the heads into the thermostat and into your radiator....if it did it couldnt get from the intake side of the radiator to the outlet side to get to the waterpump....i wouldnt even bother with it....if it fell throught the head and down into the block it will flush around down in the bottom until it can make its way back up into the head and possibly the radiator....i would be more concerned about taking advice from people that dont know how the engine coolant system flows
A crush washer wouldnt go in that hole, through the heads into the thermostat and into your radiator....if it did it couldnt get from the intake side of the radiator to the outlet side to get to the waterpump....i wouldnt even bother with it....if it fell throught the head and down into the block it will flush around down in the bottom until it can make its way back up into the head and possibly the radiator....i would be more concerned about taking advice from people that dont know how the engine coolant system flows
question
I have installed AFR 195 Eliminator heads on my 1971 LT1 which also has the 3/8" NPT hole for the temperature sending unit. The problem is that the stock sending unit has 1/2" NPT threads. I have searched for several months for a sending unit with the same resistance as the OEM gauge (new from OER) but with 3/8" NPT threads and they don't exist. 1/2" to 3/8" adapters don't work. Has anyone found a solution? I can't understand why AFR would make a head specific to a GEN I SBC without the standard size hole.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Willcox used to make a little circuit board that fit on your stock temperature gauge lugs to calibrate other senders to the stock gauge. I believe that that patent was sold to one of the big companies after Ernie passed. You can google C3 corvette adjustable resistor and most venders supply them
I had Ernie turn down a stock sender from 1/2 to 3/8s, you could find a machine shop to do it but it will cost close to $100...mine was years ago and it was $80.
Last edited by Rescue Rogers; Jun 15, 2026 at 12:36 PM.
I have installed AFR 195 Eliminator heads on my 1971 LT1 which also has the 3/8" NPT hole for the temperature sending unit. The problem is that the stock sending unit has 1/2" NPT threads. I have searched for several months for a sending unit with the same resistance as the OEM gauge (new from OER) but with 3/8" NPT threads and they don't exist. 1/2" to 3/8" adapters don't work. Has anyone found a solution? I can't understand why AFR would make a head specific to a GEN I SBC without the standard size hole.
In later models the 3/8" NPT is standard. There was a guy that was taking the 1/2" sending units and turning them down to 3/8" but I think he's gone now. You could take a 1/2" NTP sending unit to a machine shop and have them turn it down to 3/8" NPT.
I have installed AFR 195 Eliminator heads on my 1971 LT1 which also has the 3/8" NPT hole for the temperature sending unit. The problem is that the stock sending unit has 1/2" NPT threads. I have searched for several months for a sending unit with the same resistance as the OEM gauge (new from OER) but with 3/8" NPT threads and they don't exist. 1/2" to 3/8" adapters don't work. Has anyone found a solution? I can't understand why AFR would make a head specific to a GEN I SBC without the standard size hole.
My solution, mount the sender on the intake manifold. (Yes, it registers the same). Also, if you order your heads directly from AFR, they will drill the correct size hole at your request.
You can drill out the hole and tap it yourself. You can also buy the head from AFR direct and have them make the hole the bigger size for you.
I bought the tap and hugged out the small hole with a die grinder. Once the original threads are all ground out, you are very close to the correct tap drill size for the larger pipe tap to fit the original sender. Steady hand helps here.
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AFR 195 head question
