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Looking for input on my cooling numbers on my 1966 F100 with 1974 FE 390, Holley Sniper EFI, small cam, Edelbrock manifold, TREMEC TKX 5 speed trans and Hedman Headers. Champion EC 433 2 row aluminum radiator with Ledfoot Racing Aluminum Shroud with eight (8) rubber air flow flaps Plus 2-12" SPAL1522 Fans.
Recently installed a FlowKooler Hi Flow 1642 water pump and Robertshaw 330-160 hi-flow thermostat. Also Hard Candy Hose Bones Big Block kit for lower radiator hose and their Small Block kit for the upper radiator hose and fresh antifreeze. Vintage Air sure fit A/C kit (installed about 2018).
With temp at 190 degrees (by temp gauge) and engine running I see very little antifreeze movement in the radiator with the cap off, there is some, just not like I would expect (more flow movement I'd assume?).
Numbers: Outside temp 85 degrees, partly cloudy, light wind.
After 1/2 hour idle Dash Temp gauge shows 190 Degrees, T-stat housing shows 170 degrees @ the temp sending unit and 190 degrees at the water pump inlet/outlets. Shut the hood and dash temp gauge went up to 205 degrees at idle after about 15 minutes.
With A/C turned on at the 3/4 hour mark, within 10 minutes Dash Temp gauge shows 220 Degrees, T-stat housing shows 190 degrees @ the temp sending unit and 200 degrees at the water pump inlet/outlet.
Temp readings at thermostat housing and water pump were with my infrared thermometer laser gun.
I'm not sure if those numbers should alarm you, idling for 45 minutes with the AC on. Btw, thin walled headers generally release more heat in the engine compartment than manifolds, which could explain the temp rise with the hood closed.NTL, I agree that a 160 stat is too cold. Also because I've read running closer to 190 burns water and volatiles out of the oil so keeps lubrication better. Also, fwiw, my truck's fuel system isn't happy until I'm over 160 at the gauge anyway. You offered a lot of numbers, but not your cap pressure. What's your cap pressure? That's important to let you know if you are overheating, but not bursting hoses.Another important number. What's your distributor advance at idle? Low advance at idle will create hot idle. That's exactly what ported timing was meant to do in the 70’s - burn exhaust gasses at idle. Do you have mechanical advance or vacuum advance? If vacuum advance, is it hooked to ported or manifold vac? Manifold vac with your small cam at idle should run timing up near the 30’s btdc, which idles better and keeps exhaust temps low. Ported or mechanical will keep idle timing same as initial timing and make idle exhaust temps high. So check your timing at idle.
Radiator cap is 13 lbs. Distributer vacuum is ported and connected to the 3/16" ported manifold vacuum on my Sniper 4150 (550-510). I'll recheck timing at idle.
Not sure what a 390 requires, but the stock t-stat for a 352 was a 180* with a 13lb. radiator cap, as you stated. The t-stat is a Motorcraft RT 18, I believe.
Last edited by ibuzzard; May 30, 2026 at 09:23 AM.
It's true that pure water boils at 212 degrees at sea level. But if you have a good 50/50 coolant mix and a 13 PSI radiator cap that raises your boiling point to about the 260-270 degrees range. Doesn't sound like you are getting close to that range.
What is the AFR at idle? 14.7 runs the hottest, make sure it's not at 14.7. Low 14s usually makes for a more stable idle (at least with carbs) and runs cooler than 14.7.
Thanks all for the input and responses. I'll be checking out the timing and go from there. Looks like my other concerns are not that big of a deal so I'll just keep my eye on it.
I have that same Holley sniper. In addition to ports at the back, there is an NPT threaded port at the front to manifold vac, if you ultimately want to change. I attached to that one since it made a nice short run to the distributor. I found a stainless barbed fitting for a clean look, probably from McMaster Carr.
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