S4 temperature gauge oddity.

[Siena]

For what it's worth, after 166K miles, both my oil and coolant sit in the middle of the dials... So that's 90 and 120, or he other way around. Always have done, always will do.

Not in dispute at all, oil temps can be as high as 130 - 135 degrees.

But, at what engine / road speeds does your oil temp sit at 120? At idle? Regular town driving? At motorway speeds?

 

[jonnya]

If you're running something like 10-50, then you should be ok sitting at 120 degrees. However if you use a more viscous oil, ie: 10-40, which is recommended for the S4, you are in danger of the oil becoming too viscous and not protecting your engine properly.

10W40 is LESS viscous (i.e. thinner) than 10W50 not more (at 100DegC). With a thicker oil it's
normal to see higher peak oil temps. High temperatures can damage the oil, depending on
what type of oil it is. Synthetics are a lot more resistant to temperature than mineral oils.

On MY S4, normal driving, my oil is around 100. If I start really caning it, then it quickly
gets to about 120. For a track, I would definitely need an oil cooler.

 

[Blue_Thunder]

10W40 is LESS viscous (i.e. thinner) than 10W50 not more (at 100DegC).

Sorry, got my terminology wrong. I meant more fluid rather than more viscous, which I hope I got across.

Dan, how are the water temps looking?

 

[Dan Gliballs]

Well this is my dash after just idling in the drive. There's only about 2mm difference between 110 & 120 degrees, but I think we're all agreed water temp at 90 is absolutely correct, so as the water is cooling the oil then obviously the oil has to be hotter than the coolant.

Interesting pic

On the motorway journey up here it showed around 85-ish degrees for oil temp and 75-70 degrees for water (sitting at around 80-100 units of speed per hour in the 3-4 degree outside air).

We'll be doing excursions up here tomorrow, so I'll make note of how things are under stop-start low speed driving.

Many thanks for the input and opinions by everybody so far by the way

 

[GSB1]

On the motorway journey up here it showed around 85-ish degrees for oil temp and 75-70 degrees for water (sitting at around 80-100 units of speed per hour in the 3-4 degree outside air).

For motorway driving the oil temp sounds right to me, water temp reading too low.

 

[SonicDeathmonkey]

Not in dispute at all, oil temps can be as high as 130 - 135 degrees.

But, at what engine / road speeds does your oil temp sit at 120? At idle? Regular town driving? At motorway speeds?

Almost all motorway. On the way home from bristol, to be fair, the oil was about 100... as was the spedo! unless any feds are reading this. Then, the spedo said 70. honest.

 

[AndyMac]

For motorway driving the oil temp sounds right to me, water temp reading too low.

Given that we all seem to agree that the coolant should be 90, you honestly think the oil temp should be lower than the coolant. Can you explain how this is physically possible please, I'm intrigued?
Just to recap, as the name suggests, the "coolant" is there to cool the engine. How on earth can it get to 90 if the oil temp is only 85?

 

[Siena]

I travelled from Suffolk to Chelmsford, 46 miles each way, on the A12.

Speeds were between 60 and 85mph, my coolant temp sat as it always does, at 89 degrees, my oil temp varied between 75 and 100 degrees. It was a warm day today too, outside temp varied between 10 and 15 degrees.

 

[GSB1]

Given that we all seem to agree that the coolant should be 90, you honestly think the oil temp should be lower than the coolant. Can you explain how this is physically possible please, I'm intrigued?
Just to recap, as the name suggests, the "coolant" is there to cool the engine. How on earth can it get to 90 if the oil temp is only 85?

I have no idea of the physics or any other theory. I write based purely on what I personally experience with my S4. Also my expereince of my S4 tallies with the expereinces of many others with S4s on the S/RS forums.

Keep in mind that us 2.7tt drivers have a paranoid eagle eye on the oil temp guage because we drive like nuns until we see water and oil temp sufficient to feel safe enough to boot it.

It does depend on the oputside temperature, but more often than not coolant is up to 90 well before the oil temp moves off it's rest.

With "normal" driving by which I mean following the pace of moving traffic, no hard accelerating, no sitting in traffic, no hard accelerating the oil temp will often site around 80-90. Now for motorway speed driving from memory maybe more the 90 scale for oil. Spirited driving, on a warm day you might see 100. To get anywhere close to seeing the centre 120 degree mark you are talking about some serious fun, giving the car a workout on a hot hot summers day. I think I may have got the car around 110 perhaps, but never actually reached 120C.

EDIT: Just checked my pics from VMAX. Oil temp not fully in shot but you can see enough to see the white of the needle is not at the dead centre position, so even at 160mph+ oil temp was not 120C.

I have also read the Oipe Oils thread where it is explained oil temps of 120C are NOT good!

This is my expereince, with a mapped S4, and based on the fact their are many B5 S4 owners who agree, I don't believe this to be anything but the norm.

This I would say is useful information for a fellow S4 driver. As Dan's issue is water temp related, I think you should either start a new thread or leave the thread to help Dan and his water temp issue.

Dan, never seen the water guage not work it's way up to 90 in ther first 15 minutes of driving maximum and then stay there, rock solid, regardless of condition nor driving. Totally unlike oil temp that varies quite a lot.

 

[Blue_Thunder]

Saying that though, his oil temp looks perhaps a little low for doing '80-100 units of speed per hour' from Sussex to Lancaster.

Going right back to the top of the thread, I think Andymac has hit the nail on the head with a possible thermostat problem.

 

[GSB1]

Thermostat or a temp sensor. Thermostat could be fine but guage reading wrong. I think. Temp sensors are a common VAG fault. They dont last forever.

 

[Siena]

Hmm. But, the fact the oil temp readings are on the low side, for the distance covered, I'd be inclined to say the thermostat's either partially stuck open, the spring's gone soft, causing it to open earlier, or even the wrong one.

Though, if coolant temps have been up to normal range in the past, I'd say most likely the first 2 options.

My coolant temp will rise to 90 degrees withing 15 - 20 minutes of driving, and remain there.

 

[AndyMac]

I've had both these issues at different times, but admittedly on my 2.8Q not an S4. Could be both, but my moneys on the thermostat. If it was just the temp sender, the oil temp would still be reading correct at around 100-110 and it's very unlikely both the coolant temp sender and the oil temp sender go faulty at the same time.

GSB1 - of course the coolant gets up to 90 well before the oil. Water is easier to heat up than oil, so even though the oil may be 60 when partially warmed up, the coolant will reach 90 because the thermostat has shut off the rads and is purely circulating around the engine, which will reach 90 pretty quickly, while the oil lags behind. i.e. see how long it takes to boil some chip fat compared to boiling a kettle. It is the engine that is heating up both, so the oil will always lag behind.
Ultimately though once the engine is up to temp (20-30mins of driving) then the oil cannot be at a lower temp than the coolant no matter what the weather or the driving style. That is unfortunately just basic physics.

 

[GSB1]

..... the oil temp would still be reading correct at around 100-110 and it's very unlikely both the coolant temp sender and the oil temp sender go faulty at the same time.

.....
Ultimately though once the engine is up to temp (20-30mins of driving) then the oil cannot be at a lower temp than the coolant no matter what the weather or the driving style. That is unfortunately just basic physics.

I still don't think 110 is normal or a regular occurance on an S4.

 

[AndyMac]

What part of 100-110 don't you understand?
We've already established it has to be above 90, so is 100 still too high?

 

[GSB1]

Well it's higher than 90 where I said I thought my temperature would be if it wasn't hot and I wasn't giving it some beans.