Coolant temperature versus oil temperature

[dparm]

For a long time I have said that applying too much load and/or going WOT before the oil is warmed up is a good way to increase engine wear. While I won't go as far as saying this is the sole reason why some people have suffered scored cylinder walls, it is certainly a contributing factor. My advice has always been to avoid heavy load and WOT until 10-15 minutes AFTER the coolant gauge stabilizes -- because the oil will take longer to warm up.

My B8 S4 was just VAGCOM'd to show oil temp in the DIS so I thought I'd share my findings. The B6/B7 S4 is obviously a different motor but the principles are the same. If anything, the B6/B7 S4 is an even more extreme example since it has an even larger oil sump (7 versus 9 qt) and is just a bigger motor.



Ambient temperature this evening was around 30 F. My car was parked in the open so the oil was basically the same temperature -- the viscosity would be about 687cSt at this point. The oil is whatever the dealer uses (I have AudiCare), so it's likely Castrol Syntec EDGE 5w40.

I drove slowly and avoided heavy load. Within about 5-7 minutes of around-town driving, the coolant temperature stabilized. But the oil temperature wasn't even registering in the DIS, meaning it was under 140 F -- so the viscosity was over 40cSt. So yes, the [coolant] temp gauge showed the motor as warm but the oil was still far away from normal temperature!

After about 12 more minutes the oil temperature finally leveled out at 220 F, meaning it had a viscosity of about 14cSt.



So going WOT when the coolant is warm and the oil is not means that oil you're forcing through is at least three times thicker than it ideally should be! The oil pump is working extra hard to do this, and you're not going to force as much oil into the places it is needed.

When it's the dead of winter, it will take a lot longer for the oil temps to stabilize. And picking an oil that's too thick only slows that process down too. And if anyone is wondering, letting the car idle for a bit before driving it won't help much. It just dilutes the oil with fuel. Engine load will warm up the oil, not idling. If anyone with an oil temp gauge, or even a B7 owner wants to post how long it takes for oil temp to stabilize, feel free. I just wanted to give some context to the advice I had provided people with for so long.

[Blackstallion]

good info/analysis like always dparm

EDIT:This is random but any particular reason why you know your oil specs and such so well?

[QIKRNU]

AMEN.

Thank you for a very concise explanation. I believe this has been needed for some time.

[dparm]

good info/analysis like always dparm

EDIT:This is random but any particular reason why you know your oil specs and such so well?

I read a lot in my spare time. I also have a brother who is a chemical engineer (obviously he knows tribology and polymers), and my father has been a gearhead for nearly 50 years.

[dparm]

BTW, I plan to report back with my new ultra-high viscosity index "homebrew" oil cocktail that I'll be changing out for tomorrow. Anxious to see how it influences the speed with which it comes up to temperature, and how the normal operating temp changes.

[Blackstallion]

BTW, I plan to report back with my new homebrew oil cocktail that I'll be changing out for tomorrow. Anxious to see how it influences the speed with which it comes up to temperature, and how the "normal" temp changes.

haha!

keep us posted...

[Axel-]

If anyone with an oil temp gauge, or even a B7 owner wants to post how long it takes for oil temp to stabilize, feel free. I just wanted to give some context to the advice I had provided people with for so long.

I don't have my oil temp gauge properly hooked up yet but VAGCOM has oil temp reading so I'll hook up my VAGCOM and see if I can get you some data for the B7 tomorrow.

[dparm]

Awesome. Would be interesting to see the reported oil temperature right when the coolant temperature levels off.

[Das Audi]

I don't have my oil temp gauge properly hooked up yet but VAGCOM has oil temp reading so I'll hook up my VAGCOM and see if I can get you some data for the B7 tomorrow.

Looking forward to your results considering we live in the same temperature zone and drive 4.2s.

[Das Audi]

BTW, I plan to report back with my new ultra-high viscosity index "homebrew" oil cocktail that I'll be changing out for tomorrow. Anxious to see how it influences the speed with which it comes up to temperature, and how the normal operating temp changes.

Corn oil?

[Axel-]

I'll log both coolant and oil temps in VCDS, output it to Excel and make a line graph showing both temps rising. Should help visualize the difference.

[Graze]

B7 RS4, ambient temp in Australia (Brisbane - approximates to Miama FL) is different to most of US. The B7 has a warning not to exceed 7000rpm til oil temp reaches 50degC (122degF). I restrict revs to 4000rpm in this phase - allows good smooth gear changes without loading the motor. That takes me about 1km of normal load driving. I then give it another 3-5min before I rev it over 5000rpm. By then it is at 80-90degF (176-194degF). Norla operating temp is about 100-105 deg C unless under extreme k load (track when it can get up to 122deg C (250 degF). hope that helps

Graze

[65vetteC6]

I will also try to get out tomorrow and log oil temp and pressure in VAG. Its supposed to be a high of 40 so it should be a decent representation.

[dparm]

Corn oil?

LOL no, it's just two different viscosity oils mixed in a certain ratio to get me what I want.

[vhstejskal]

Very cool thread topic. Other than using an oil temp gauge having a baseline to when your oil get to temp is good to know. I've wonder why some car manufacturers don't incorporate water/oil heat exchangers. Probably cost but would help with getting the right viscosity sooner prolonging engine life.

Lastly, the factory oil cooler somewhat serves this purpose but isn't adequate for true shorter time to op temp.

[event]

Thanks for the post OP, really wishing I had an oil temp gauge.

[Axel-]

From this morning. As you can see, the coolant temps plateau at about 9 and a half minutes. However, the oil temp doesn't reach optimum temperature until about minute 20.
Edit: This was normal slow city driving. I believe highway driving would accelerate everything.

http://docs.google.com/a/gauntlet.ne...x=4kho6akvuven

For anyone wanting to see the original chart and data:

http://docs.google.com/spreadsheet/c...kI3Nm5PUTVacXc

[dparm]

Cool graph, Axel. Similar to what I saw: coolant stabilizes 5-10 minutes before the oil. I would assume it was fairly cold in Toronto today (around 0 C).

Just curious, what oil are you running? Any upgrades to the lubrication or cooling systems for that SC?

Also, what are your typical oil temps around town?

[Kookie]

From this morning. As you can see, the coolant temps plateau at about 9 and a half minutes. However, the oil temp doesn't reach optimum temperature until about minute 20.
Edit: This was normal slow city driving. I believe highway driving would accelerate everything.



For anyone wanting to see the original chart and data:

https://docs.google.com/spreadsheet/...kI3Nm5PUTVacXc

Cool graph, Axel. Similar to what I saw: coolant stabilizes 5-10 minutes before the oil. I would assume it was fairly cold in Toronto today (around 0 C).

Just curious, what oil are you running? Any upgrades to the lubrication or cooling systems for that SC?

Also, what are your typical oil temps around town?

Dparm, as usual, your post is incredibly helpful.

Axel, thank you for posting a graph so quickly

Hopefully we see more of these motors preserved and cared for properly.

[dparm]

No problem man. It's a community and we're all here to share and help each other out.

I see no reason these cars can't run for a very long time. Plenty of examples out there now with well over 100k on them.

[Axel-]

Cool graph, Axel. Similar to what I saw: coolant stabilizes 5-10 minutes before the oil. I would assume it was fairly cold in Toronto today (around 0 C).

Just curious, what oil are you running? Any upgrades to the lubrication or cooling systems for that SC?

Also, what are your typical oil temps around town?

My mechanic uses Liqui Moly 5w40 Toptech 4100
No additional cooling systems for the SC from an intake aspect. The only difference is an open cone air filter in the back passenger side with some cutting of the original ducting for greater air flow (to get cold air from the outside front of the car directly to the cone filter as the engine bay gets quite hot). Also, rubber strips removed to keep things cooler (that rubber gets really hot).

However, there is an oil cooler kit (and auxiliary radiator delete) installed for the oil for the sc.

It was fairly chilly, about 3c. Car was parked overnight in an underground garage at around 14c (which is why the temps start there and not 3c). It would have probably taken an extra 5-10 minutes had it been left outside all night.
Typical oil temps are 95c I believe if I don't push the car hard.

[dparm]

Surprised he's using Toptec 4100...not optimal for North American fuels.

Thanks for the reply.

[RicardoTG]

This is an awesome thread; thanks dparm and Axel- for some amazing information. I have some potentially dumb questions.

1. Which temperature is more indicitive of the engine block temperature?
2. Does the oil pump operation depend on engine load (i.e. does the pump change speed depending on RPM)? I'm tempted to think that the throughput of the oil pump would be based on oil viscosity and not engine speed. This would mean that the engine will certainly suffer from lack of lube in cold temps, but also that wear on the oil pump is independent of the weight of the driver's right foot.
3. Also however and in addition, isn't our multi-grade 0w40/5w40 oil supposed to reach an acceptable viscosity more quickly? Or is that just a gimmick?

Just trying to get some clarity as to exactly how high RPMs at low temps cause additional wear. I'm at 160k on my 2005 B6, and while I don't have to deal with sub-freezing temps in socal, I want to make sure my baby reaches at least 250k.

[dparm]

High engine load (not necessarily RPM) on a cold engine causes additional wear because:

1. The oil is thicker and does not carry heat away as quickly
2. The oil is thicker and cannot be pumped into the needed areas as quickly
3. Some of the oil additives and even the base chemistry are not fully 'activated' until higher temps are achieved (the molecules literally re-align)
4. The oil pump/filter may very well be operating in bypass mode
5. The oil is not hot enough to have burned off any moisture that accumulated


Multi-grade does indeed offer the benefits of better protection across all temperatures, yes.

[ken5018]

Great info dparm! Thanks for the graph Axel! It always good to see proof in writing instead of just talk!

[QIKRNU]

This is an awesome thread; thanks dparm and Axel- for some amazing information. I have some potentially dumb questions.

1. Which temperature is more indicitive of the engine block temperature?
2. Does the oil pump operation depend on engine load (i.e. does the pump change speed depending on RPM)? I'm tempted to think that the throughput of the oil pump would be based on oil viscosity and not engine speed. This would mean that the engine will certainly suffer from lack of lube in cold temps, but also that wear on the oil pump is independent of the weight of the driver's right foot.
3. Also however and in addition, isn't our multi-grade 0w40/5w40 oil supposed to reach an acceptable viscosity more quickly? Or is that just a gimmick?

Just trying to get some clarity as to exactly how high RPMs at low temps cause additional wear. I'm at 160k on my 2005 B6, and while I don't have to deal with sub-freezing temps in socal, I want to make sure my baby reaches at least 250k.

#1 Block temperature is not nearly as important as oil temp, although they are closely related.

#2 I may be wrong, but I have not seen an automotive oil pump that was not directly related to engine speed.

[quattroloco]

ohfuck what have i done... my poor turbos.

i may consider this before deciding mid coolant temp means BRaaaaaaaaaaaaaaaP POW BRaaaaaaaaaa... well, you get the point.

no more hotrodding to get milk n eggs.

[S4 lynx]

dparm,
Strong work! Thank you for the time and effort devoted to this research and your teaching on the subject. I know this is slightly off topic, so please forgive me. What would cause an Audi approved synthetic 5w40 to burn in the summer but not in the spring/winter/fall. Obviously, one would expect the oil temperature to perhaps run a little higher in the summer, but given that the coolant temperature gauge is rock steady once warmed up, why should the ambient temperature make a significant difference in oil consumption? Thanks in advance.

[dparm]

Oil temperatures will be the same year round. These are water-cooled cars, not air-cooled.

[Axel-]

dparm,
Strong work! Thank you for the time and effort devoted to this research and your teaching on the subject. I know this is slightly off topic, so please forgive me. What would cause an Audi approved synthetic 5w40 to burn in the summer but not in the spring/summer/fall. Obviously, one would expect the oil temperature to perhaps run a little higher in the summer, but given that the coolant temperature gauge is rock steady once warmed up, why should the ambient temperature make a significant difference in oil consumption? Thanks in advance.

Do you mean winter? You write "summer but not in the spring/summer/fall"

Would it have anything to do with colder temps at startup regarding the seals and stuff?

[S4 lynx]

Oil temperatures will be the same year round. These are water-cooled cars, not air-cooled.

Thanks dparm,
Of course, I recognize that the car is water cooled. Ultimately though, the radiator has to transfer the heat to the air. So my question is given the superior ability of cooler ambient external air to cool the coolant via the radiator in the winter, could there be at least temporary spikes in oil temperature in the summer months relative to the winter months? Perhaps this would not be detected by the coolant gauge? I sure dont claim to be a maven on the topic and am just thinking out loud.

[S4 lynx]

Axel,
Sorry, my mistake. I edited my post above. I meant to say oil loss in summer only, but not spring, fall or winter. Having said this, that is an interesting hypothesis regarding seals, etc. Thanks!

[65vetteC6]

Logged some data today, coolant leveled out after 10 minutes. Then oil leveled at around 93*C after another 5 minutes of highway driving. Outside temp was 32*F. I logged the data, or so I thought, just gotta find it.

[dparm]

Thanks dparm,
Of course, I recognize that the car is water cooled. Ultimately though, the radiator has to transfer the heat to the air. So my question is given the superior ability of cooler ambient external air to cool the coolant via the radiator in the winter, could there be at least temporary spikes in oil temperature in the summer months relative to the winter months? Perhaps this would not be detected by the coolant gauge? I sure dont claim to be a maven on the topic and am just thinking out loud.

Nah, not really. The oil will come up to temp a bit faster, but the operational temps shouldn't vary unless you're out on a track.

[TypeRx]

FYI, this morning on my RS4 (18 degree F ambient temp), it took about 5-6 minutes of driving for the oil temp to start registering (7000 rpm limit turns off and oil was at around 145 degrees F) and about 20 minutes before it reached full operating temp.

[Axel-]

Logged some data today, coolant leveled out after 10 minutes. Then oil leveled at around 93*C after another 5 minutes of highway driving. Outside temp was 32*F. I logged the data, or so I thought, just gotta find it.

Yeah, the highway driving will accelerator warm up over slower stop and go city driving.

[the huff]

FYI, this morning on my RS4 (18 degree F ambient temp), it took about 5-6 minutes of driving for the oil temp to start registering (7000 rpm limit turns off and oil was at around 145 degrees F) and about 20 minutes before it reached full operating temp.

So say for arguments sake, it takes on average 20 mins for the oil to hit full temp, how harmful is it to be running the engine for just 20 mins at a time in the morning? My commute is right around the 20 min mark, 4 lane divided highway w/ light or no traffic (if I'm out of the house on time), about 10 lights, speed limits float between 40 and 50 MPH most of the way.

[ilko]

Your oil would be up to temp in that type of environment, I wouldn't worry about it.

What you need to worry about in short trips is water condensation. As oil cools after the car's been driven it is normal for the steam to become water. Obviously water and oil don't mix so what you need to do is drive the car so the oil can reach operating temp and the water will evaporate. If your driving style includes many short trips where oil temp doesn't get hot enough you would need to change the oil more often.

[the huff]

Your oil would be up to temp in that type of environment, I wouldn't worry about it.

What you need to worry about in short trips is water condensation. As oil cools after the car's been driven it is normal for the steam to become water. Obviously water and oil don't mix so what you need to do is drive the car so the oil can reach operating temp and the water will evaporate. If your driving style includes many short trips where oil temp doesn't get hot enough you would need to change the oil more often.

Ok, think I'm starting to get it...so the real downside of shorter trips is contamination of the oil, which then inhibits it's ability to its job, ultimately leading to premature engine wear. I sent in a sample for UOA to Blackstone before Thanksgiving, but still waiting on report. Oil had about 4500 on it, about 3000 of those since I've owned the car. I'd say 80% of my driving is like this, though I should see some more longer HW trips with ski season here. Should I consider more frequent changes than 5k?

[ilko]

Let's see what Blackstone says. I had done a lot of short trips on my previous A4 over the course of an oil change once and the report came back showing insignificant amount of fuel and other contaminants. So as long as you take a nice long trip once a week you should be OK.