Motor swap temp gauge question
 

My 83 GP has a 69 350 pontiac in it. The car was originally a 3.8 v-6 with the gauge pack. The temp gauge always worked flawlessly with the v-6. After the swap to the 350 a new aluminum rad and 16" spal electric fan went in for cooling and an edelbrock p4b manifold and 4 barrel carb went on. The sending unit for the water temp gauge is to the right of the t-stat housing (160 stat) and is for a 305 chevy. My gauge reads really hot almost right after firing up. Would the v-6 gauge require a different sending unit than the v-8? are there different resistance values? The car doesn't seem to run hot, and my cooling system is basically brand new, except for the water pump. I don't have a temperature gun, so i'm asking this question as a first course of action.

Thanks in advance!

You have to use the temp sender for the engine not the car. Once you get the correct sender installed you will probley get the proper reading. You can mix the senders from one engine brand & expect it to work for a different engine. Thats why they make so many different senders. Go to the local parts store & get one for the pontiac 350 engine & you will be ok.

The temp sender for the Grand Prix with 3.8 and gage package is the right one. You may have to use an adapter to make it fit. Try to find a hubless adapter and use care not to apply excess sealer, as the the sender is ground. The gage converts resistance to a temp scale on the face of the gage and it does not care what brand engine the sender is screwed in to.

I had a feeling I needed to use the sender specific to the gauge. I'll get a bushing and see what's up.

When you say "hubless" you mean a physically shorter bushing/adapter right? Had no luck at the Depot, and the Speed Shop was closed by the time I got out there. With a standard 3/8x1/2 adapter the sending unit barely pokes out the bottom and is really tough to thread in because of the slight taper.

I went to the hardware store and got a bushing with no hex for a wrench. It just has inside and outside pipe threads. It sort of looks like a ring.

I wasn't able to find a hubless one at the Depot. Basically, I put it in the vise with the hex still intact, and tapped the rest of it all the way down. Then I cut the hex off. The only issue is that i'm not sure the probe is far enough down into the intake manifold. It reads about 65-70 degrees celcius on the gauge. 160 farenheight is 71 celcius, so it's potentially reading cool. I'm closer though.

Its probably right. If any air was in the crossover it would migrate out through th t-stat.