low/high oil pressure

I have a 1998 Olds Aurora (220,000 mi) took it to Co., ran just fine, oil changes EVERY 3000 mi using 10/30 Synthetic oil since it had 96,000 mi on it, got to Co.on 2nd day of trip oil pressure dropped to 0 when idling and overheated, decided to rent car for time we were in Co.Drove Aurora back to Il. making sure not to let it idle, ran fine as long as we kept rpms up. Both GM dealer and Cadillac dealers told us would be cheaper to find another engine. So we found one with 56,000 miles on it, had our son change motors, got it home a month ago and its doing the same exact thing!! Any ideas guys??? Oil pressure goes up to 95psi then slowly goes down to 20psi, then up to 95 and down to 20 continuously, down to 0 if I let it idle too long.

An engine was changed before putting a mechanical gauge on the engine, to check the oil sender/sensor?

An engine was changed before putting a mechanical gauge on the engine, to check the oil sender/sensor?
The dealership in Co. said bearings were out and also said they didn't have fitting to put gauge on(it was a holiday weekend, so no one wanted to work on it) ,so we took car back to Il. and put another 2500 miles on it before finding an engine from Aims out of Florida. Car drove fine as long as we kept rpms up, no knocking, smoking, etc.

The dealership in Co. said bearings were out and also said they didn't have fitting to put gauge on(it was a holiday weekend, so no one wanted to work on it) ,

OK, shame in them...... a dealership does not have a fitting to check the oil pressure on their own car?



so we took car back to Il. and put another 2500 miles on it before finding an engine from Aims out of Florida. Car drove fine as long as we kept rpms up, no knocking, smoking, etc.

If the "bearings were out", those bearings would be singing at higher rpms.....



This all starts with the Service Manager......he represents the shop.....if the shop doesn't have the fitting, he gets one, immediately, even if he has to borrow it from a competitor......our shop would always go that extra step to help a customer, especially someone who broke down and did not live nearby....It's shops like this that give dealerships, whether they be GM, Ford, Chrysler, etc., a bad rap.....just like anything that happens, you rarely hear the good things that dealerships do, you just hear the bad....one bad incident out of 100 is more than enough to erase the 99 jobs that go without complaint....

The dealership in Co. said bearings were out and also said they didn't have fitting to put gauge on(it was a holiday weekend, so no one wanted to work on it) ,

OK, shame in them...... a dealership does not have a fitting to check the oil pressure on their own car?



so we took car back to Il. and put another 2500 miles on it before finding an engine from Aims out of Florida. Car drove fine as long as we kept rpms up, no knocking, smoking, etc.

If the "bearings were out", those bearings would be singing at higher rpms.....



This all starts with the Service Manager......he represents the shop.....if the shop doesn't have the fitting, he gets one, immediately, even if he has to borrow it from a competitor......our shop would always go that extra step to help a customer, especially someone who broke down and did not live nearby....It's shops like this that give dealerships, whether they be GM, Ford, Chrysler, etc., a bad rap.....just like anything that happens, you rarely hear the good things that dealerships do, you just hear the bad....one bad incident out of 100 is more than enough to erase the 99 jobs that go without complaint....
I agree, don't know what to do now...