Which temp gauge to go by

[JG72]

My 402 engine was rebuilt and runs great, I have factory gauges which always seemed accurate and also installed auto meter set up for back up. The auto gauge under the dash reads a 190 temp cruising on my BB. The new sender unit in the drivers head and in the dash gauge reads 220-230. Which one should I go by? Concern is running very hot on dash gauge. I used a temp gun to check block and t-housing and both temp gauges match what I'm reading. Thoughts? Thanks guys. Didn't read this anywhere else in the forum.

 

[420ponies]

Your factory gauge will read "hottest" because emissions back then had it turned up from the factory. It's the Autometer gauge I would go by. Where is your Autometer  sender located?   What degree stat are you running? I'd go -20deg.on where you want it to run. I'm running a 180degree and never gets over 200 degrees and has a lopey camshaft.

 

Edited July 23, 2021 by 420ponies
Added content

[jft69z]

I have a dakota digital sender in the left cylinder head, and the Holley EFI sender at the t-stat housing. The Holley one reads 15-18 degrees less than the one in the head. The temp gun at the t-stat seems to be right on the money. 

[JG72]

Auto meter sender next to T-state housing in manifold and Running a 180 thermostat. I take it with the motor being a fresh rebuild with bigger cam etc. it will run hotter. The old engine ran at 190 on the factory gauge which is why I ask compared to now. Thanks for the reply's! 

[MC1of80]

Go by the autometer gauge. 

With the sender in the head, the temp will be hotter than by the thermostat housing. 

[Dtret]

I agree with the above posts. Go by the Autometer. But you may want to try and lower the head temp. IMO the head temp is too hot. 

[JG72]

Agreed on head temp being to hot. Changed the H.D. clutch fan today and was stunned the engine temp dropped 20 degrees on both gauges. It also really ran a lot better.

[Glen]

Have you considered electric fans?  Mine kick on at 190 (using factory temp gauge) if AC is not being run.

AC on?  Fans run continuously. Drops the temperature back down to right around 165-ish in about a minute. I didn’t realize how much air those things pull through the radiator (not sure what CFM they’re rated for as they came with the vehicle and I haven’t looked that closely... yet). 

Not to mention it’s fun to pop open the hood while it’s running and watching people jump back when those fans kick on... they startle almost everyone the first time they experience it  

 

[Glen]

Forgot to mention the additional load requires a bigger alternator. I believe it has a 130 amp now.