pl2000n

My 1969 L36 is freshly rebuilt. The crankshaft mains and pins were ground down 0.010" shortly before I bought the long block. I measured measured the mains and pins (0 deg and 90 deg, in two places) and everything was in spec. I installed new Clevite bearings. I measured oil clearances with plastigage and the mains were all over 0.002" but not by much. One was close to 0.0025" which is near the service limit according to the service manual, but everything looked really good and were close in value. After removing the plastigauge, I squirt plenty of Lucas lube an torqued down the caps. I also installed a new Melling M77 pump and did not change the relief spring. When cold, oil pressure is very good and varies as you'd expect with RPM. When completely warmed up after driving for a while, oil pressure drops to 35psi (as shown on the stock dash gauge), and really fall flat (to a scary lever) at idle. I chock it up to oil viscosity decreasing once fully warm. I'm using Mobil 1 10W-30. Any suggestions? Should I increase viscosity? Thank you.

Cool95vette

My 383 oil pressure would drop to about 8-10 lbs at idle after it got up to temperature. I put a high volume pump in and it's up to 15 at idle. I'm using synthetic 10w-30 also.

Les

Are you 100% sure that your gauge is accurate? I ask because the hot idle PSI on my modded L36, while technically acceptable, was lower than I thought it should be. I connected a gauge that I knew to be accurate and found that the factory gauge was reading several PSI low.

derekderek

10w30 is gas mileage oil. For getting leetle 4-bangers up to 30 mpg for Corp avg fuel economy. 20-50, 30 or 40 I feel is preferable. You have so much more stuff to oil at idle, but the real thing is heavy loads and film strength. My 1.5 Prius torque is rated in inch/lbs, I think. Maybe mm/gms. When those 427 pistons are trying to push that crank through the mains at 6500 rpm's, you want oil that will be more amenable to staying in those bearings.

ddawson

M1 10-30 Viscosity @ 100ºC = 10.1
M1 00-40 Viscosity @ 100ºC = 12.9

I use 0W-40.

pl2000n

Thanks Les, no, I'm not sure the OEM gauge is accurate, but the 454 that was in the car when I bought it last year, showed better oil pressure after it was warmed up. I'll put a real gauge on and see what I get. What do you read at hot idle?

pl2000n

Thanks. Per Les's reply, I'm going to install a real gauge and see what I get.

blue427

I have gone through 4 after market Corvette gauges,they are crap.Right after having my engine rebuilt by a very good builder it was reading 17 lbs at idle.Some of them would get stuck at 35 lbs no matter what the rpms were.I put a $20 Sunpro gauge in that I had laying around the garage and it works perfectly.I copper lined it to the engine.When hot I get 30 to 35 lbs at idle.I checked the gauge for accuracy before putting it in. I use 15-40 dino oil(the car never sits outside in the cold,garage is heated. I would check the gauge first.

drwet

I had the same problem with my 383. Clearances were a bit loose and the oil pressure was low with 10W-30. I switched to 15W-50 and a high volume pump. Solved the problem. I know what you're thinking. What happened to that engine? Broke the crank last year. Pretty sure that had nothing to do with oil pressure.

7T1vette

How much oil pressure do you think the engine needs, when it's idling?

Les

I couldn't remember the specifics, so I did a search and found my old thread. This may save 7T1vette from having to retype his info too.

https://www.corvetteforum.com/forums...ure-gauge.html

pl2000n

Thank you Les for the link (informative) and everyone else for you comments. I plugged in a real gauge. When cold, I get 25psi at idle and 50psi revved up. When hot, I get about 12 psi at idle and 45 psi revved. Is it time to consider a higher viscosity or is this acceptable?

riverracer au

the old rule of thumb was 10psi per 1000rpm

ajrothm

.0025" on the mains is a bit much for 10w/30. I would go 15w/40 or something of that nature... (I run Chevron Delo 10w/40) in my 496. That should pick you up about 4-5 psi hot...

I know the old rule of 10 psi per 1000 rpms but..... You get out running it hard and the oil temp is 250*, your 10 psi at idle will be 5 psi.... I can't live with that kind of stress.... For me personally, anything under 20 psi at idle is too low.

Throw some 40w in it and see what it does.....Get it good and hot...Not idling in the driveway.


For comparison, using a new repro stock gauge, cold idle is around 65 psi, hot idle after free way driving is 35 psi.... every now and then it dips below 35 if I'm making hard highway pulls and then idle it....but not below 30 ish.

drwet

You're probably OK, but those numbers do make me a little nervous. I would try a higher viscosity oil, and if you're still uncomfortable with it, switch to a high volume pump.

pl2000n

Thank guys, I'll try a higher viscosity oil. On bearings, does anyone know if Clevite (MS829P10 for mains, CB743P10 for connecting rods) tend to run a little thin, thus giving more oil clearance? I ask because the crank mic'd out perfectly.

jhopper408

Mine did the same thing on my 383S. I put a new guage in. Problem solve.

Rescue Rogers

I use mobil1 15w50 racing oil. It has High zddp and zinc and You can get it in 5 gallon jugs at walmart for $23. Cant beat the price. I had a chevy performance high volume reg pressure pump when I rebuilt my motor and just put in a Melling high pressure regular volume pump. MY pressure with with the high volume pump was no higher than 35 cold or hot but would drop at idle when the motor was hot. Im ordering a high pressure spring for my high volume pump if I think I need it in the future

After some research and the fact that I like the higher revs, I went with the Mellings pump. when its cold I get 75psi and as it heats up its around 65 psi. at idle it drops down around 5 to 8 psi on the stock gauge but it isnt accurate that low. But the research I read says you need a high volume pump with clearances that large to maintain your pressure.

HeadsU.P.

Volume and pressure are two different varibles on oil pumps. You can move a lot of oil with high volume but low pressure. You can have high pressure with low volume.
Volume is determined by the size of the gears in the pump itself. HI Vol gears are a little bit longer than std.
Pressure is determined by the color of spring selected in the pump.

7T1vette

Wow! I didn't know that Fluid Dynamics was so easy!!