I don't want aftermarket gauges in my 66 and i only have idiot lights so I'm using a mr gasket radiator cap with a temp gauge in it. I'm curious if anyone has used both a radiator cap gauge and a regular aftermarket gauge that goes in the intake. Wondering how accurate this cap gauge is as I was fighting an over heating issue, while driving I obviously can't monitor the temp but I would drive around town a while the stop and check it. It wouldn't boil over until I got home and shut it off with the gauge reading anywhere from 240-260. I changed my fan and shroud and now it stays around 180-190 and did reach 200 once sitting in the driveway while I was tuning it, it took quite some time to get there. I guess what I'm getting at is if these cap gauges read the same as a gauge where the sending unit is in the intake or do the possible read higher or lower?

 

A cap gauge would read lower.

 

By how much?

 

It depends, but it WILL be different and lower. If the t-stat is closed it will be a LOT lower. The bottom line is that the radiator cap gauge is worthless. If you don't want gauges visible in the passenger compartment, you can put them in the glove box. You can also install a mechanical or electrical temp gauge temporarily under the dash with a clamp and remove it when you diagnose the problem. If you REALLY don't want a gauge wire through the firewall, then use a mechanical gauge under the hood, with the sensor in the manifold where it belongs. From a convenience standpoint this is no different than using your gauge-in-cap, but it will be a LOT more accurate.

 

It's not about running anything through the firewall I just like the basic look of the car without extra aftermarket gauges. I actually would like a rally pack gauge cluster so I can monitor the car. I do like the idea of running a gauge under the hood though, I may just put one temporarily under the dash so I can watch it while driving

 

I hooked a mechanical one into a spare port, ran it through the firewall, and I just taped it to the underside of the dash as I did not want to drill it. It falls down a lot, and I plan to remove it soon and go back to stock as my stock gauge is accurate.