I changed my oil today and put a new oil pressure sending unit on. Now the pressure is lower than normal. Any ideas why?

 

It could be your old sender was reading high, your new one reads low, or you used a poor flowing (aka FRAM) filter on it. You'll need a good quality mechanical gauge to see what the pressure really is. How low does it get at a hot idle?

 

About 20 psi. The motor has a lot of miles and the oil pump was starting to read low.

 

did you use teflon tape when you installed the new sending unit? or put anything else on the threads?

 

No, but if i remember correctly I think it had something on the threads. It doesn't leak if that is what you are wondering.

At highway speeds it reads about 30 now and before it read around 40 when warmed up.

 

well, if you did put something on the threads, you need to take the sending unit out and clean it off. since the threaded area acts as ground for the sending unit, anything on the threads will interfere with the connection.

 

General rule of thumbs for the SBC is 10psi/1000rpm engine speed. At hot idle, 20psi is fine, nothing wrong with that.

What filter did you have before? What one now? What oil before/after?

 

I have heard that rule before too.

I always run a Fram PH 30.

Thats interesting about the threads being covered. I might have to take it out and double check.

 

i got a simular problem but backwards i have very high pressure and my pcv valve pops off i just had my oil changed and it did change a bit so im lost other than that it runs good but not good if its doing this

 

You need sealer on pipe threads. It won't interfere with conductivity, the mating parts of the threads will wear right though it as it's tightened.

 

I never used any sealer on the threads, and i have about 30 psi oil pressure at hot idle, and I've never lost a drop of oil. I prefer not to use any sealant, because i have seen oil pressure gauges give incorrect or no readings because of teflon tape on the threads. There are sealants that are made for use on sending units, if you do use a sealant make sure you get one of those.

 

Irock87, just check and make sure you didn't over fill your oil. I once had a problem with a transmission where the dipstick that came in it was 2" to short.