Help me understand pressures

[Superchickenn]

Hi everyone I'm looking for some guidance.

I have posted on here recently as I'm having oil pressure issues with my golf 1.8t.

I've installed a digital pressure guage to determine if the warning lights are being in trustworthy.

I purchased this car with a smashed sump, I then set about repairing said sump.

All was well.. during the sump replacement I checked the bearings and all was good there... put it all back together and drove it and again all was well.. or so I thought..

After a little while I kept having the low oil pressure warning so rigged up a digital pressure reader and indeed my pressures were low on idle... to be fair the car had done 196000 miles..

Therefore last night I fitted a new pump.. however same issues today and I have been logging whilst driving to try and find a trend...

The oil pump is driven off the crank via a chain so should match engine speeds... here is what I've discovered and my associated questions..

The car has given today a oil pressure of 8-12 psi on warm warm idle (fine when slightly warm or cold) when should be around 14+

Secondly when driving around 1500 rpm the oil pressure warning beeps too low even reading 18-22 psi on the display.

The biggest thing I have noticed that I don't understand is.....

When off the throttle at 1500 rpm the oil pressure shows 38psi when light to full throttle is applied pressure drops to 18-22psi and beep... I don't understand how this could be if chain driven off the crank.. can anyone explain please?

[anonymous-user]

How often do you need to top up the oil and how much oil do you have to put in?

[anonymous-user]

Also,

• What oil are you using?

You could try a thicker viscosity to see if that helps maintain pressure, but it's a bodge rather then a fix.

• Do you know how far the car was driven after the sump got smashed?

You say you've checked the main bearings. Another possibility is camshaft bearings, especially if the top end suffered oil starvation after the sump damage.

[Superchickenn]

rockin said:

How often do you need to top up the oil and how much oil do you have to put in?

The car has only done 250 miles and has had 4 oil changes so wouldn't know.. sorry

I got 20l drums of oil and just pour what I need

[Superchickenn]

Nanook said:

Your oil pressure is not going to be higher when the engine is warm. I'd expect pressure to be lower at idle when the car is warm, than when it is cold, as oil is not as viscous when it's warm.

Got enough oil in it? If you don't, there could be aeration, which can cause pressure to drop. Same can happen if there's too much.

Yes I full agree.. and plenty of oil.. have even over filled on one occasion with no difference..

Stone cold the idle is 68 psi warm ish idle is 30 psi ..

Apparently vw say min warm idle is 0.9bar so 14 psi

[Superchickenn]

rockin said:

Also,

• What oil are you using?

You could try a thicker viscosity to see if that helps maintain pressure, but it's a bodge rather then a fix.

• Do you know how far the car was driven after the sump got smashed?

You say you've checked the main bearings. Another possibility is camshaft bearings, especially if the top end suffered oil starvation after the sump damage.

I've tried 5w 30 recommends and now running 10w 40 to see if that would help..

This car is having a hammering in September (ring trip) so trying to iron out the faults..

The guy said (use this term loosly) was turned straight off.

I haven't checked the cams yet that was my next option really

[Superchickenn]

Nanook said:

Superchickenn said:

rockin said:

How often do you need to top up the oil and how much oil do you have to put in?

The car has only done 250 miles and has had 4 oil changes so wouldn't know.. sorry

I got 20l drums of oil and just pour what I need

Just keep doing that til it dies then.

It's a Golf that's most of the way to the moon, just run it til it goes bang.

I have another nice 1.8t that I didn't want to take to the ring hence buying this thing on a punt.

I was thinking about running 60 weight oil but would rather fix

[Superchickenn]

Nanook said:

Superchickenn said:

Yes I full agree.. and plenty of oil.. have even over filled on one occasion with no difference..

Stone cold the idle is 68 psi warm ish idle is 30 psi ..

Apparently vw say min warm idle is 0.9bar so 14 psi

OK. You said

"The car has given today a oil pressure of 8-12 psi on warm warm idle (fine when slightly warm or cold) when should be around 14+"

I took from that, that 8-12 PSI was fine when slightly warm or cold, but that you'd expect to see 14+ when it's 'warm warm'

And I've read it another half a dozen times, and that's still what it says, so I'm not sure what you mean

Sorry buddy vw say it should be 14+psi

But today on warm warm idle after a good drive of 45 mins she was idling lower on the pressures I mentioned. Hope that helps.

My biggest confusion is why the pressure increases when I lift off to when I accelerate when it's connected to the main crank so should stay the same in my theory

[TooMany2cvs]

As a rough and generic rule of thumb, you want to be looking at 1 bar of oil pressure per 1k rpm, warm and above idle. 14.5psi = 1 bar.

200k mile engine bought with a smashed sump? I'm not sure I'd even be bothering to diagnose. A used VAG 1.8T is not exactly rocking horse st, is it?

[Superchickenn]

TooMany2cvs said:

As a rough and generic rule of thumb, you want to be looking at 1 bar of oil pressure per 1k rpm, warm and above idle. 14.5psi = 1 bar.

200k mile engine bought with a smashed sump? I'm not sure I'd even be bothering to diagnose. A used VAG 1.8T is not exactly rocking horse st, is it?

I agree but if it could be something simple im missing hence asking here once my knowledge has been exhausted...

I dont understand why the PSI goes up when i lift off the throttle when RPM's are staring the same

[Mave]

Superchickenn said:

I agree but if it could be something simple im missing hence asking here once my knowledge has been exhausted...

I dont understand why the PSI goes up when i lift off the throttle when RPM's are staring the same

What's the pressure referenced back to? If it's referenced back to the crankcase, it could be that the rings are worn and / or the breather blocked, so the crankcase pressure is causing the reading to drop when you open the throttle.

[Superchickenn]

Mave said:

Superchickenn said:

I agree but if it could be something simple im missing hence asking here once my knowledge has been exhausted...

I dont understand why the PSI goes up when i lift off the throttle when RPM's are staring the same

What's the pressure referenced back to? If it's referenced back to the crankcase, it could be that the rings are worn and / or the breather blocked, so the crankcase pressure is causing the reading to drop when you open the throttle.

The 1.8t's come a spare sensor port... its at the top of the oil cooler.. right next to the standard oil pressure sensor ... hope thats what you referring to

[Mave]

Superchickenn said:

I have another nice 1.8t that I didn't want to take to the ring hence buying this thing on a punt.

I was thinking about running 60 weight oil but would rather fix

I don't think running 60 oil is the answer unless you're worried about consumption. You're trying to get the right amount of oil to the right parts of the engine - putting thicker oil in just makes the oil pressure light go out!

[Superchickenn]

Mave said:

Superchickenn said:

I have another nice 1.8t that I didn't want to take to the ring hence buying this thing on a punt.

I was thinking about running 60 weight oil but would rather fix

I don't think running 60 oil is the answer unless you're worried about consumption. You're trying to get the right amount of oil to the right parts of the engine - putting thicker oil in just makes the oil pressure light go out!

Thats it Mave i would rather find a fix if possible..

[TooLateForAName]

How cracked was the sump? Did you check the oil pickup for damage?

[SouthHamsGaz]

Having changed the pump i expect the answer to this to be yes, but worth asking anyway. Did you check the oil pick up pipe? They are notorious for getting blocked on those engines.

[Mave]

Superchickenn said:

The 1.8t's come a spare sensor port... its at the top of the oil cooler.. right next to the standard oil pressure sensor ... hope thats what you referring to

I wasn't referring to anything specific as I'm not familiar with the 1.8t - just going back to basics. If the oil pressure has dropped it's because the feed pressure has dropped or the sink pressure has increased - I was thinking of the latter as a less obvious possibility. Reasons the feed pressure might drop are change in viscosity (probably not in this case) or change in flow (either because the pump isn't putting it into the system, or its leaking out somewhere!) What condition is the turbo in? Any sign of oil leaking out under boost?

[Superchickenn]

TooLateForAName said:

How cracked was the sump? Did you check the oil pickup for damage?

Cracked wasnt the word... smashed...but the pick up was like brand new .. and clear

[Superchickenn]

SouthHamsGaz said:

Having changed the pump i expect the answer to this to be yes, but worth asking anyway. Did you check the oil pick up pipe? They are notorious for getting blocked on those engines.

good guess... yes i checked it and it was fine... but also blasted it with carb cleaner to ensure it was clear

[Superchickenn]

Mave said:

Superchickenn said:

The 1.8t's come a spare sensor port... its at the top of the oil cooler.. right next to the standard oil pressure sensor ... hope thats what you referring to

I wasn't referring to anything specific as I'm not familiar with the 1.8t - just going back to basics. If the oil pressure has dropped it's because the feed pressure has dropped or the sink pressure has increased - I was thinking of the latter as a less obvious possibility. Reasons the feed pressure might drop are change in viscosity (probably not in this case) or change in flow (either because the pump isn't putting it into the system, or its leaking out somewhere!) What condition is the turbo in? Any sign of oil leaking out under boost?

turbo seems good.. no smoke and pulls hard .. i havent checked the play yet... i may look at that later

no oil leaks on the car either