Oil Pressure changing with heater position

[TUS 2 CON]

Bit of an odd one this. I had a bit of a shock the other day when I noticed that my oil pressure reading was down to 17/18 PSI while I was idling in traffic. I immediately stopped and checked the oil level, which seemed to be fine, but I topped it up with a litre of Mobil 1 just to be on the safe side. On the journey back it was back up to 27/28 at idle in traffic and the sort of readings you would expect under load.

I was out today, sitting in traffic again, when I noticed I was getting low readings again. I was a bit surprised at it suddenly happening, because I had been out for a while and keeping an eye on the pressure. It then clicked that I had turned the heater dial down to it's coldest setting just before I noticed the drop. I turned the heater back up to hot and, sure enough, the oil pressure reading immediately went up by 10 PSI. Experimenting with it, the two are definitely related because as you turn the dial you can watch the pressure change instantaneously. Funny thing is, the heater fan was turned off - it's just the temp dial I was turning.

Any ideas what the problem might be? The car is a 2005 mk2.

[fredd1e]

poor earth somewhere?

[Walford]

fit a mechanical gauge,and check the electronic reading that way

[Arapo]

I am getting a lower oil pressure when I am turning the aircon on.

Was worried at first, but then I was told that its normal since the idle revs drop, and so does the oil pressure. You learn a new thing every day..! :-)

Could it be that you somehow turn the aircon on as well?

[Walford]

Arapo said:

I am getting a lower oil pressure when I am turning the aircon on.

Was worried at first, but then I was told that its normal since the idle revs drop, and so does the oil pressure. You learn a new thing every day..! :-)

Could it be that you somehow turn the aircon on as well?

How low psi ??????

[Arapo]

If I remember correctly, revs drop by around 200 when the aircon is on, and from around 16PSI oil pressure that it normally shows when warmed up in idle, it goes down to 12PSI or so.

My Tuscan is a MK1 Tuscan by the way, and from what I was told oil pressure depends on the oil used - right? Should I start getting worried??

[Walford]

I would not trust the transponder/ECU/dash to within 5 psi maybe you should check the pressure with a quality gauge and take it from there

[TUS 2 CON]

Arapo said:

I am getting a lower oil pressure when I am turning the aircon on.

Was worried at first, but then I was told that its normal since the idle revs drop, and so does the oil pressure. You learn a new thing every day..! :-)

Could it be that you somehow turn the aircon on as well?

No, it drops regardless of whether the aircon is on or not. The thing it seems to be related to is simply the position of the heater dial. My feeling is that it is (in my case) a poor earth somewhere as suggested above. In support of this, one of the guys at Power (when I last popped in) told me he thought I had a poor earth because my rev counter and speedo needles were 'flickering' more than normal.

I've checked the oil levels again which has given me some confidence. I also found this on Graham Varley's Sagaris page "With fresh Mobil 1 5W/40 mine runs on idle ;- 20deg 65 psi , 30deg 50psi, 40degC 35psi, 65degC 25psi.", which is about what I'm getting if I leave the heater dial alone.

[Arapo]

Walford said:

I would not trust the transponder/ECU/dash to within 5 psi maybe you should check the pressure with a quality gauge and take it from there

You overestimate my knowledge and abilities... :-)

Edited by Arapo on Monday 18th April 17:58