Oil Pressure: Vauxhall 1.8 SOHC

[Randal Tarn]

As usual when I seviced my car over the Christmas break, I replaced the old Mobil 1 0-40W with the same.

 

My car is a Vauxhall 1.8 SOHC powered Classic which had done 4,000 miles.

 

However, some 500 miles further on I see a noticable drop in Hot Oil Pressure, from 4 Bar to 3 Bar at 3,000 + RPM and from 2 Bar to 1.5 Bar (just touching the red) at idle.

 

Blipping the throttle gives a quick response form the guage, so I am presuming that neither the pump, nor the guage are completely knackered.

 

Cold oil pressure is a steady 4 Bar for about 10 minutes, so I also presume the pressure relief valve is not completely shot. (This may not be logical but it suits my non mechanical brain to think this way.)

 

The temperature guage shows as it always has, ie the water temperature is not rising any more quickly than previously.

 

No sign of oil on the outside of the head, block, sump, or garage floor.

 

No sign of oil and water mixing to be seen on the dipstick, the oil filler cap or the water expansion tank.

 

The car is running as well as it ever has.

 

I have a number of questions therefore:

1. Should I be panicing???

 

2. Arnie Webb stated recently that he felt there was a issue with Mobil 1 0-40W Hot Oil Pressure on all Vauxhall Engines. Mine is not a twin cam, so may not have been included in his thoughts. But do the experts out there believe that 15-50 would be a better oil to use, given that half my sevening mileage is on the 12 mile trip to work, ie car not fully warmed up until the end of the journey?

 

3. Is it possible that the composition / spec of Mobil 1 0 - 40W has changed between Christmas 2000 and Christmas 2001 giving the drop in pressure

 

4. Caterham Guages are legendary for their approximation of the true situation, is a gradual decline in pressure reading consistent with this syndrome?

 

5. Finally, if all above points to a problem....where do I look to find the cause and hopefully the solution.

 

Many thanks for any assistance

 

 

Randal V92 FPF

[C7JFM]

for what its worth...my 1.6 sohc VX does just the same and it doesn't bother me abit. The engine is healthy and i presume this a characteristic.

[8vastra]

i think mobil 1 has changed spec, but i would say it was too thin an oil to use myself.

my 1.8 8v didnt behave in this way, but i ran it on vauxhall 10W40 and it was fine.

the relief valve only comes into play on full throttle AFAIK

i take it the pressure is taken from by the oil filter. are you running an oil cooler? these are supposed to open at 92 degrees, which 'might' explain the pressure drop when the engine is up to temp, but it should stay strong when going above 3k revs.

which 1.8 engine is it? as the early one runs very low idle oil pressure (one of the things revised in the later engines) so isnt too much of a worry.

[Randal Tarn]

Thanks for the feedback so far.

 

Perhaps I should look where I am going and not at the Guage.

 

I do not have an Oil cooler, but the connection to the pressure sender is down in the area, above and behind, the Oil Filter.

 

The engine is a pre 1993 unit, I believe originally used on the Astra GSI (8V).

 

I am pleased to hear that low idle pressure was a characteristic of older VX 1.8 SOHC engines, and I assume as described above mine is one of those.

 

Randal.

[AndreK]

Randal

Wouldn't worry too much my Vx 1.6 is only slightly better on the pressures, using Castrol synthetic 0w/40. A 5w/40 Synthetic would probably be even better though when hot?

 

[EFA]

A 5/40 like Comma SynerG will give a firm 2 bar when hot even when thrashed around the track!

 

At 3000 rpm you should be getting at least 3.5bar.

 

Fat Arn

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