Switched My L-82 over to Mobile 1 , 10W-30W today. Fugured since I've driven all my cars to 300,000 & My diesel Truck to 450,000 Miles it should be good for my !973 Vette.
Left Town for home Oil pressure was running About 45# like normal. But about 5 miles out of Town the pressure dropped to 25#. If i let off of it. the pressure would climb back up to 45#. So I eased it on home. Went to town & bought some 10W-30W Penzoil & zinc additive. Changed it out & presto Oil pressure back up at Steady 45+ pounds.
Whats up with that?
Then I adjusted right side hood latch. Whoops it won't open. But I did read up on that in the forum. What a pain in the backside.

 

This is typical. Your L82 wasn't built for synthetic oil.

 

When Mobil 1 first came out many years ago I tried it in our '73 w/454. It hot idled at 15 lbs. Took it out immediately.

 

What zinc additive did you buy?

 

So your saying it runs at #25 at cruise but if you let off the throttle the pressure climbs to #45. I see no way this could even happen. That said both of the other posts are just plain wrong. A SBC needs #10 of oil pressure per 1000 RPM. If you get that running 10W-30 it is fine. If your idle pressure jumps to 35 or 40 at idle with 20W-50 is it better? No. That said Mobil 1 10W-30 does not have adequate ZDDP for flat tappet cam protection and additives are not the way to go.
Synthetic has a lot of benefits over conventional oil too numerous to even go into here but a major one is drastically improved cold start protection where 90% of engine wear occurs.
A thinner oil has many benefits over a thicker oil also too numerous to even go into here but a major one is that oil is not only a lubricant but a coolant for internal engine parts. Lower viscocity oil has more flow volume even though pressure is less cooling the internals better than thicker viscocity.
True synthetic oil is not a problem in any Chevy V8 in good condition with good gaskets and likely the main reason your car engines are running 300,000 trouble free miles and your diesel has 450,000 without a rebuild.
There are so many myths and misconceptions out there on this subject and they just keep getting spread by being repeated over and over. Read deep into the oil sticky and do some in depth research on this to clear up the myths.

 

But synthetic oil was built for his L82 if it has adequate ZDDP.

 

I ran Mobil 1 10W-30 in my '76 since 1990 and never had a problem. If anything, the oil pressure increased slightly.

 

I just put Mobil 1 10W-30 in the 82 a few weeks ago, and I noticed the same results as above. A cold start-up and I am at 40 lbs +, after it warms up it is 35-30 lbs or lower depending on the type of driving, when increasing speed on the highway it goes back up to 40 or more. as soon as you back off the r's, it lowers again. just my results...
Now the PO used nothing but Castrol oil and before I changed it was always on 40 lbs., and I think he only used conventional oil...

 

I use Mobil one 10w-30 in my stock '81 with 96K on it and average 40-45psi constantly

 

Synthetic is a smaller molecule meaning given the same weight oils the syn will pour thinner.
The lower oil pressure when it warms up is nothign to worry about its good stuff. You dont need 30-40 lbs all the time.
Use a thicker weight syn and your pressure will read the same its just easier on your oil pump and cam gears.

 

I always wondered what simple 'tease' in the topic line would bring the most people out of the woodwork ready to do battle.

Anybody want to take a guess as to WHY the pressure dropped in OP's engine?

 

I'll be using Mobil 1 15W-50. From the Mobil 1 website, they state "Boosted, higher viscosity, advanced full synthetic formula designed for performance vehicles. HT/HS applications. Racing and Flat tappet applications." It contains higher levels of zinc and phosphorus, 1300 and 1200 ppm respectively.

 

Why does he mention only using Zinc the second time around?

 

How is that relevant?

 

lets hear your guess

 

I have been using Mobil 1 in my 78 L-82 since 1985! I currently use 15W-50 the last few years since the EPA lowered the ZDDP levels in mass merchandised regular grade oils. There is absolutely no way that the correct grade oil from one brand to the next would be causing the oil pressure issue you are having. A 10W-30 grade oil of any brand is a 10W-30 grade oil regardless of whether synthetic or conventional oil. The only brand of Mobil1 suitable for a flat tappet cam engine is 15W-50-1,200/1,300 ZDDP, which is what I currently use in my stock L-82-66,000 miles-All interns are original-pistons, cam, crank, heads etc.

PS-Just an aside on Mobil 1-Just replaced the head gasket on my all original Kohler 15 HP lawn tractor engine that has 2,000 hours on it. I have run 5W-30 Mobil 1 in the Kohler since day one. The piston and valve train looked BRAND new at 2,000 hours. I can still see the swirl marks from the honing machine in the casting when the Cylinder was bored! Pretty incredible!

 

I use Mobil 15W50 in my '81. It has 1200-1300 ZDDP. ( Some Mobil 1 synthetic oils do not contain this level of ZDDP.)

 

All in due time.

 

excellent real world info, many thanks

 

What your seeing is not an issue. It is typical of any multigrade oil synthetic or conventional. Cold oil always has higher pressue than operating temperature oil. The lack of ZDDP in Mobil 1 10W-30 is an issue.
Your symptoms are not like the op. He states that at cruise he is at #25 and when he lets off the throttle the oil pressure increases to #45. I don't understand how that is possible. It is contrary to basic physics.