Thinner Oil, Lower pressure?

[frubes]

I had my oil changed for the first time since I bought my 350i a couple of months ago.

I asked what oil to put in and got recommended 0W40. I think the mechanic said he put in 10w40 or maybe 10w50. Not sure what was in there to start.

Before the oil change the car would idle around 50 lb/" on oil pressure and go up to about 80 lb/" under hard load.

Now though it idles around 30-40 and only goes up to about 50 under load. Is that normal? Is it prehaps thinner oil lowering the pressure? I have checked the level and it looks ok.


Also it used to have a noisy tappet at start up that quickly went away as soon as it was warm. Now it is noisy all the time, I wonder if it is due to the lower oil pressure not getting the oil into the tappet? Any suggestions, shall i top it up with more oil, or put some thick oil in to thicken it?

[TVRleigh_BBWR]

Idealy you want more of a 15-20/40-50
The SD1 and LR Engines that the wedges are based on was a 20/50, if you was a serp. engine with the Crank driven pump then I'd maybe put a 10/xx but not in an early engine, esp if the pump gears are worn.

[GreenV8S]

frubes said:

Before the oil change the car would idle around 50 lb/" on oil pressure and go up to about 80 lb/" under hard load.

Wouldn't put too much faith in the gauge being accurate unless you've checked it, but if that's a true reading it's worryingly high.

frubes said:

Now though it idles around 30-40 and only goes up to about 50 under load. Is that normal? Is it prehaps thinner oil lowering the pressure? I have checked the level and it looks ok.

Still a little higher than average but not by enough to worry about.

[frubes]

50 is half way up the gauge, so cant be that high? Basically i need to get the thick stuff back in there!

[GreenV8S]

frubes said:

50 is half way up the gauge, so cant be that high?

That's faulty logic. 50 psi is at the top end of what's healthy. Significantly more than that and there's something wrong. You may be suffering from insufficient oil flow, and you will also be wearing the cam / oil pump drive gears excessively (which will then knacker your timing). You really can have too much of a good thing.

[Brap_Brap]

frubes said:

50 is half way up the gauge, so cant be that high? Basically i need to get the thick stuff back in there!

"Thick" is somewhat of a misnomer. Oil comes with 2 numbers.... for example, 10w40 is ten and forty.... ten references the "thickness" (or runniness) when cold, "forty" when hot.

I live in a climate that regularly drops temperature to -30C. A 0W or 5W oil is good for ice cold starting, but in summer I'll run 10w30 or 10w40. What I'm trying to say is that with England's climate, a 0W-anything is really uncalled for. 10w50 would suit your climate just fine.

So, as far as "thickness" goes, remember, each number on a quart of oil means a different extreme. If you pick a 0-weight oil designed for -20C or more, and start your car with it at +15C, no fkn wonder your oil pressure seams low and the oil seems "too runny". Until the oil gets hot, you're running it out of its designed range.

Edited by Brap_Brap on Saturday 23 May 09:28

[wedgefettler]

I've been using Millers CFS 10W-60 's for years.
The Rover engine, especially the pre-serpentine is an old design of unit,
and doesn't like oil that's too thin.

[gsx600]

Just changed my oil and my presure has halved

Before was using VR1 Racing 20/50 and was getting 40 - 50 max and about 20 - 30 minimum

Now only getting 18 - 20 hot or cold

Might have to go back to VR1 on next change

[rev-erend]

gsx600 said:

Just changed my oil and my presure has halved

Before was using VR1 Racing 20/50 and was getting 40 - 50 max and about 20 - 30 minimum

Now only getting 18 - 20 hot or cold

Might have to go back to VR1 on next change

Is that a fair comparison though .. don't forget you have had your oil pump apart.. so might even be a bit of oil on the sender wire.

What was the grade of oil that you got off Leigh - I know he had a load of extra virgin olive oil to get shot of

Edited by rev-erend on Wednesday 27th May 09:50

[TVRleigh_BBWR]

gsx600 said:

Just changed my oil and my presure has halved

Before was using VR1 Racing 20/50 and was getting 40 - 50 max and about 20 - 30 minimum

Now only getting 18 - 20 hot or cold

Might have to go back to VR1 on next change

Would have thought you should still get a larger change that that. you may still have a problem with the pressure valve.
I'm getting 50PSI cold on the Racer and 40-60 running hot. with the same oil, but I have a crank driven pump. so dont think it's the oil.

[gsx600]

No not the relief valve now ,as when I changed the valve and before the oil change, was getting near 50 psi, but on new oil around 20 psi

[Emmdat]

Not sure if this helps any but came across the following details in relation to the SD1 3.5ltr V8,

Cold 40-50 psi at 2400 rpm
Warm 27-35 psi at 2400 rpm
Warm 15-20 psi when idling

15W40 - Recommended for temperate Climates
20W50 - Use if evidence of slightly worn bearings

Incidentally, not many were sold on the idea of using synthetic oils in the above engine but did acknowledge that TVR had recommended the use of synthetic in their Rover based V8's. For my own information can anyone advise what TVR did to the base units that resulted in a synthetic recommendation?

[rev-erend]

TVR / Land Rover introduced the serpentine front assembly which included a better oil pump.

[TVRleigh_BBWR]

rev-erend said:

TVR / Land Rover introduced the serpentine front assembly which included a better oil pump.

Not in the wedge era

[JR]

Emmdat said:

Not sure if this helps any but came across the following details in relation to the SD1 3.5ltr V8,

Cold 40-50 psi at 2400 rpm
Warm 27-35 psi at 2400 rpm
Warm 15-20 psi when idling

15W40 - Recommended for temperate Climates
20W50 - Use if evidence of slightly worn bearings

Incidentally, not many were sold on the idea of using synthetic oils in the above engine but did acknowledge that TVR had recommended the use of synthetic in their Rover based V8's. For my own information can anyone advise what TVR did to the base units that resulted in a synthetic recommendation?

That's pretty much the same as what TVR said: 2bar at 2K revs when hot. I am not aware that TVR did anything specifically when they switched to synthetic oil; I believe it was on the basis that synthetic oil takes longer to break down than mineral oil.

[350zwelgje]

JR said:

Emmdat said:

Not sure if this helps any but came across the following details in relation to the SD1 3.5ltr V8,

Cold 40-50 psi at 2400 rpm
Warm 27-35 psi at 2400 rpm
Warm 15-20 psi when idling

15W40 - Recommended for temperate Climates
20W50 - Use if evidence of slightly worn bearings

Incidentally, not many were sold on the idea of using synthetic oils in the above engine but did acknowledge that TVR had recommended the use of synthetic in their Rover based V8's. For my own information can anyone advise what TVR did to the base units that resulted in a synthetic recommendation?

That's pretty much the same as what TVR said: 2bar at 2K revs when hot. I am not aware that TVR did anything specifically when they switched to synthetic oil; I believe it was on the basis that synthetic oil takes longer to break down than mineral oil.

+1
Probably sucking eggs here, but it gives me something to post ;-)

Synthetic is better quality (sort of in simple terms) the grading/rating depends on industry standards/norms the oil should comply to.
Mineral 20/50 and synthetic 20/50 do have (should have, as only tests can prove it in an academic way) the same viscosity-wise..... The higher the number the lower it will flow in a test, that is set at defined temperatures. Coldstart needs therefore low numbers at ambient temperature to minimise friction and get the pressure up as quickly as possible. RV8 with larger tolerances than modern designs need thicker and thus higher numbers at same operating temperatures when warm (and not too low when cold, like 0 or even 5. Only under extreme cold circumstances: the northpole).

Think that later RV8s were built to better known tolerances (only non-standard RV8 by TVR: 4.0 with 240BHP (even Rover asked if it was possible to use this for their MG RV8, Peter said no), 4.3, 5.0 and later the 4.5.
This & experience (and commercial deal...) took TVR into synthetic and higher viscosity as in Mobil1. Also like to think that TVR always used what was 'lying around' and they were into the AJP V8 (while still putting the RV8 5.0 into the griff as the AJP took longer to develop) that requires and can handle higher viscosity and is able to put more power out (higher numbers is higher friction).

Anyway, the non-serpentine RV8s need flow and not pressure. And compared to other engines (mainly more modern) the pressure is relatively low. But it is designed for that and it works fine, even in todays world. Especially if you consider how many people still use this engine for racing and in the past rallys like Dakar.

Sorry to type away like this. Do I qualify for being an anorak now?

Rob

[adam quantrill]

The anorak's in the post ;^)

There might be another thing going on here - what does the oil pressure gauge read when you turn on the ignition and haven't started the engine? If it's reading below the zero line there might be an explanation for some of what you are experiencing. What might have happened is this:

1) original thick oil plus possibly an occasionally sticking relief valve resulting in 'too high' pressure, especially when cold, overdriving the pressure sensor
2) sensor diaphragm is now slightly distorted and now reads lower (can happen with age too)
3) now it sounds like the engine oil pressure is more normal and don't forget the weather is warmer

So it might not be that surprising that your readings are different, maybe I can't explain the whole of the apparent drop, but at least some of it.

Try putting a known good pressure gauge on the warning switch port to calibrate your in-car gauge, you might find (like I did) that it's under-reading.