I'm swapping my computer-controlled Buick 231 V6 out of my '81 Grand Prix, and putting a Buick 350 in its place. My car had idiot lights but I'm also swapping in a factory gauge cluster. I'll install a gauge sender for the electric oil gauge in the cluster. Without the CCC system the check engine light is useless so I want to use it as an oil light (an attention-getter) so I'll also install a switch sender. Many people do this on a tee at the switch location. The 3rd thing I'd like to do is to put a mechanical gauge in the engine compartment - I'd run a copper line & mount it on the passenger wheel well. It'll be useful after the swap (trust that over the electric gauge) and I figure why not just leave it there permanently? My question is - is there any good reason not to do this... any harm in having three connections all together (assuming I can find a fitting to make it work)?
No reason not to. I ran a three-way T on my nailhead, to have a pressure switch for oil pressure loss to cut fuel pump (0-3psi), a mechanical oil pressure gauge, and the switch for the light. Just make sure you use a steel nipple. I used a three inch brass nipple and it work hardened and cracked at the threads at the block. Leaked a bit so I caught it before it was a problem. Have run it with the steel for about 4 years and 20k miles with no issues.
The copper line over time could break due to the flexing of the engine. If you mounted the gage directly on the engine it wouldn't be a problem. Otherwise use a braided line if you must mount the gage directly to a fixed location on the body like the fenderwell. I say this as I've had a copper line break in the engine compartment. Made quite a mess as it was for an oil pressure gage. I was able to get the engine shut down before it ran out of oil thank goodness! Put on quite a smoke show too!
I wouldn’t bother with a gauge under the hood, too risky, it could be leaking or whatever and you wouldn’t know. Besides who drives from the engine compartment
I'd leave a capped port accessible for tuning under the hood, but definitely dont leave a gauge there long term.
Because the engine, body & frame are constantly flexing independently of each other you MUST put a loop in the copper tubing or else it will eventually break. Just like the brake lines coming off the master cylinder. Tom T.
