Oil pressure gauge from mechanical to electric.

[63 Chevy Stepside]

I am putting a 1991 motor into my 63 and would like to use the original oil pressure gauge. What is the best way to do that with my 1991 350 Engine? I also want to use the water temp, but I think if I find the wires from the 91’s computer for the temp and run them to the temp gauge that should work, right?

[Alan's Classic]

Moved ya to engine and drivetrain, plus a bump. You will get some help here.

[63 Chevy Stepside]

Thanks!

[ray_mcavoy]

Hi 63 Chevy Stepside,

Does the 91's computer wiring tie into the oil pressure switch? They often do that as a safety for the electric fuel pump. If so, you can keep your truck's existing mechanical oil gauge with the new engine by doing the following:

(1) Temporarily remove the electric sending unit from the new engine.
(2) Install a short pipe nipple in the hole (usually either 1/8" or 1/4" NPT).
(3) Thread a Tee fitting onto that nipple.
(4) Reinstall the electric sending unit in one leg of the Tee.
(5) Connect the tube from the stock oil pressure gauge to the other leg of the Tee.

GM often used two temperature sending units on their computer controlled engines in the 80's and 90's. One sending unit for the computer (usually a 2-wire one in the intake). You can leave that sending unit as-is.

The other sending unit is for the gauge or idiot light (often a 1-wire one in the driver side cylinder head). The resistance of the 91 sending unit probably won't be correct for your 63's gauge. But you should be able to replace this sending unit with the one from your old engine (or an equivalent replacement meant for a 63) and hook it up to the stock temp gauge. The only catch might be if the threads in the 91 heads are smaller than the 63 sending unit. If that's the case, you might have to see if you can find a smaller threaded sending unit with the same resistance range.

[63 Chevy Stepside]

Thanks Ray,
I haven't gotten into the temp sensor wiring yet, my shop manual and wiring manual are in the mail as I write. I will check it out when it gets here. The oil pressure fix sounds great, Thanks so much for your advice.
Rick