Oil Pressure drop

[Cuppa]

Today it was pretty hot. We drove our car (without the Tvan) up a steep, very tight & windy hill which went for 16kms. We were in 2nd high/2wd all the way, except for dropping back to first on a couple of extra tight hairpins. For anyone who knows it it was the road in Mt Field NP, Tassie, up to Lake Dobson. 2000 to 2500rpm all the way. Coolant temp went up to 92 & EGR's were around 400.

Toward the top it became apparent that the oil pressure had dropped a little. At 2300rpm it would normally show about 59/60psi on the gauge once warmed up. It had dropped to about 52psi & at 2000rpm was at about 40psi. If I revved it harder I could still get the reading to rise to 61psi (the max it usually shows when hot) & when slowing down the minimum oil pressure remained at around 20/21psi which is normal.

We parked at the top & spend about 1.5 hours walking around the lake before returning to the car. When we did oil pressures were back to normal & remained so all the way back down the hill to the camp site.

Oil is semi synthetic Penrite HPR 15 (15w50).

This has happened once before under very similar circumstances, about 3 weeks ago ie long steep slow hill on a very hot day - except that one was bitumen & towing the Tvan.

On both occasions the smell of a hot motor has been quite noticeable when exiting the car at the top of the hill, but subsequently readings have quickly returned to normal & remained so.

Oil level is correct on the dipstick & hasn't changed.

QUESTION: I'm thinking the semi synthetic oil must 'thin out' when it gets hot, (& hoping that if so it still does he job it's intended to do). Am I right & would oil thinning out on a steep incline cause a drop in pressure reading in a TD42.

No nasty noises, no factory oil light.

[PeeBee]

Hot oil will present as lower oil pressure against cold oil. These are not disturbing numbers Cuppa. You can compensate for this oil pressure drop relative to viscosity in hydraulic systems with control valves, however perhaps simplest to say is that oil pressure is simply system resistance to flow, so as oil heats up, it thins and flows more readily. You mentioned the oil pressure did raise with a blip of rpm, this is exactly to my point as your pump is increasing flow i would imagine V rpm, so greater flow = more resistance = higher displayed pressure. If the oil pressure dropped dramatically and stayed there I would be concerned if hot though, however this does not seem to be the case.

[jff45]

Cuppa, without checking the manual I get the impression your figures are above factory spec. From memory, TD42 idle pressure hot is around 11 psi.

[Winnie]

Cuppa, without checking the manual I get the impression your figures are above factory spec. From memory, TD42 idle pressure hot is around 11 psi.

Mine idles at 25psi and drives at 50psi

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[mudski]

Mine idles at 25psi and drives at 50psi

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When the motor has been driven for hours and the oil would be screaming hot, it will idle around the 11psi - 15psi mark. Normal town driving it would idle around 20-25...