I changed engines in my 36, I used the gauges that were in the car when i bought it, (Mallory). I did not use the old oil sending unit on the new motor. I put a new one on. (Same configuration and style.....) The oil pressure reads 100 at idle, then goes to 75 when driving. I have never experienced the oil pressure decrease with rpm, usually it will increase as the engine revs. I bought the short block built by a local shop and it has a melling oil pump. Could the sending unit be the culprit? I use Brad Penn 20-50w oil and wix filter. The engine is a sbc.
Something is goofy there. I would buy an inexpensive mechanical gauge (Autozone, Pep Boys, etc) and use some appropriate brass pipe fittings to screw it directly into the spot where the sender goes, as a temporary way to see what your engine is really putting out. The threads on the back of those gauges is something like 1/8 npt , the same as most ports where you screw in the sender, so with some short brass pipe and a coupling you can make it clear the block. I had something going on with the gauge in my 27 recently, the pressure would drop to zero occasionally. I did the trick I mentioned above and the pressure was actually 50 psi at idle and 70 at higher rpms. I replaced the sender and it started reading correctly. You need to know what your oil pressure actually is at the block before you can move from there, and this is the cheapest, easiest way to find out. Don
Go get the old sender. I spent an ass load of money chasing an overheating condition that I thought I had. I hooked up my 58 Ply gauge to a 63 Chrysler sender in the new to me engine. When nothing else worked I went out back and swapped out the 58 sender into my 63 engine and suddenly I had no overheating situation. Same company only 5 years apart but they were not compatible. Imperial radiators with A/C fans and fan shrouds...All wasted money chasing my tail. I never even had a problem. The sending unit must match the gauge.
20-50 is way too thick for new street motor. A high volume pump(BBC) will also help create too much pressure.
You're welcome. I should have clarified, the gauge you are looking for is one that is normally made to mount in a dash, and comes with plastic line to plumb the oil to the gauge from the motor. All you do is forget all that plumbing and afix some Home Depot short brass pipe to it, with female coupler, and screw it into where the sender goes. It makes a temporary direct reading gauge out of a $ 15 item. Then, once you have established that your oil pressure is normal, you can begin chasing what is wrong. Don
Don, I finally got to hooking up a mechanical gauge and the reading was close to the electric, the mechanical gauges pressure went up when revved, the electric went down. I replaced the electric sending unit with an a new SW sending unit, (my gauges are mallory), and all is good. It is working as it should. Thanks
Happened on my 69 wrong sender .I was pegged at idle .....It is a Pontiac motor .....Reason why its dropping oil is getting warm and thin ,Could be a high volume pump .I would try another sender first......................
There was a article in a magizine awhile back about this and it was the oil filter restricting causing the lower pressure
The Jalopy Journal
