What should the V8 oil pressure be at idle?

[ESPREE]

Hey everyone,

It's been a while, but my 99 V8 is finally nearing the end of a long rebuild that was due to sandblasting/powdercoating damage (new block, oil pump, oil coolers, oil lines, bearings, etc.).  

 

We started it up yesterday (first time in about a year and half), and it ran smoothly overall, but 1-2 valves were tapping (new tappets), and the oil pressure light was flickering at idle (once it had warmed up a bit).  Pre-rebuild that light never came on.

 

We had installed an aftermarket oil pressure gauge a while back, and it was reading about 20psi most of the time, and down to 15psi once hot (taken from an oil filter adapter ring).  At this point the oil pressure tell light in the dash was coming on, which makes sense since I believe it is supposed to come on under 20psi.

 

The owner's manual says minimum oil pressure should be 1.4 bar at hot idle (which is 20.3 psi), but the mechanic reported that the minimum oil pressure in the service manual is like 5psi.  Is that correct for the V8s or just the 4 cylinder models?

 

The general rule of thumb I often hear is to have 10 psi per 1000 RPMs, which would also mean 15 psi is fine (at about 800 RPMs), but I'd like to know what other V8 owners are really getting.

 

Is 15-20psi oil pressure ok at hot idle or should I be concerned?

 

Thanks for any info!

[sailorbob]

The service notes workshop manual states 1.4 bar minimum oil pressure at idle when hot.

[ESPREE]

The service notes workshop manual states 1.4 bar minimum oil pressure at idle when hot.

Thanks, - yes this is 20.3 psi, so the current pressure seems low once it warms up.

 

Any thoughts on what could be the cause?

[Bibs]

What grade of oil are you using?

[ESPREE]

Hi Bibs,

That's a good question, though I don't know the answer.    I know he used conventional oil on this first fill for the break-in, but I don't know the weight.  It's about 32 degrees F here.

 

I would be very glad if it's just a matter of putting a different oil in!

 

He mentioned trying a different oil first (and checking the pressure with an analog gauge), so I guess we'll see how it goes this week.

 

Do you know what the current oil recommendation is?  Last I had seen, there was a TSB around 2000 for:

 

Cold: 0-15W

Hot: 40-60

 

Specifically Mobil 1 Motorsport 15W/50 and Castrol Formula RS 10W/60 (but neither of these are around anymore).

[fmxa]

You can still get Mobil1 15W/50 (even that mecca of high end shopping WalMart has it - http://www.walmart.com/ip/Mobil-1-15W-50-5-Quart/20713647).  Personally I use Redline 15W/50 - 

 

http://www.redlineoil.com/product.aspx?pid=6

Edited February 17, 2014 by fmxa

[sailorbob]

The minimum oil pressures when hot are given as:

 

Idle - 1.4 bar

3500 rpm - 2.4 bar

6500 rpm - 3.1 bar

 

Regarding causes of low oil pressure, these can be;

 

Wrong oil grade

Worn oil pump

Faulty oil pressure release valve

Excessive bearing clearances

Oil too hot

Oil level too low

 

Whilst the original oil specified by Lotus was Mobil 1 5W50 and 5W30 they also stated that any good oil could be used providing it has a maximum low temperature viscosity grade of 15W and a minimum high temperature viscosity grade of 40.

[ESPREE]

Thanks, everyone for the info!  The new oil is going in today and we'll see how it goes. 

[ESPREE]

Good news!  Mechanic reports that the valve tap went away this morning (the oil must have worked its way in there), and then he drained the conventional oil to refill it with the "normal" Mobil 1 synthetic 15W-50.  

 

Pressure went up to steady 23psi at hot idle, and the warning light has not come on at all (since pressure is above 20psi).

 

Whew!  Now he's got to go back to something different to complete the break-in (conventional again), but at least we can breathe a little easier knowing there is nothing mechanically wrong with it.

 

Thanks for the info, everyone!

[Bibs]

Good news