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So a little history first. I bought a 67 Camaro with the original block 327 with 462 or 291 heads on it ( I can check tonight if it make s a difference). I installed an Atomic Efi from MSD and it has been running great. This weekend I installed a PRC aluminum radiator and dual electric fans and having the ecu control the fans. I installed the temp switch for efi in the rear of the Edelbrock RPM Air Gap manifold and my normal Auto meter gauge is in the front of the manifold by the water neck.

My issue is that both my gauges (one in handheld for EFI and the other under the dash) are reading 70 degrees difference. The temp by water neck is the hotter of the two to the point that my fans wont kick on until the mechanical gauge is reading almost 240 degrees.

I understand that I can switch the sending unit locations and see what that does. Also, I have a thermostat housing spacer with a port for a sending unit I can install and try and get both up front.

My biggest question is: Is this normal to have such a difference between the front and back of a motor?

Thanks, Erik
 

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I was told not to put my EFI ECT sensor in the rear of the manifold since circulation is so poor back there, it's kinda a dead end. My question would be is the probe for the mechanical gauge "bottoming out" in the front intake port...

Your heads might not have a coolant port on them but if so, I bought a cheapo gauge kit at the parts store and it had a full set of different sized reducer bushings in it so I was able to use one of them to put my Auto Meter mechanical gauge in the head.

To answer the temp spread question though, 20 degrees or so is more of the spread you should see.


And I know it sounds stupid to mention, but make sure the ECT sensor is not actually in the vacuum port on the back of the intake. I only mention it because I bought a Blazer a long time ago that someone had done that to.
 

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I have a mechanical gauge in each head and there is less than 5* difference. the passenger side head (gauge toward back)does read a couple degrees hotter
 

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Steiner is correct, the back ports on the Airgap are tapped but has no flow unless you got it going somewhere.
I plumbed these two holes to an adapter block just under my T-stat to eliminate that hot spot. No flow there also causes corrosion on some intakes.
If that fan switch is set for 240°, might do what Kevin is saying, go to the head which would be the hottest spot.
Just wondering where that MSD EFI unit has the air temp sensor.
I have seen some guys add a adjustable capillary style temp sensor switch into the radiator hose inlet. Have more control with the off/on , you could stagger the second fan to come on later , main fan runs constant.
 
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