Oil warm up time: GC (Castrol Syntec 0W-30) vs. BC (Castrol Syntec 5W-40)

[eliminator]

What kind of car is this? i don't see it mentioned, but assume its a VW since the VAG-COM is mentioned.

Is it a 1.8t? If so, maybe the GC warms up faster because it flows better at low temps, and can flow through the oil cooler faster than BC. Since the 1.8t has an oil/water heat exchanger, the engine coolant actually heats the oil during warmup.

Just a thought.

-Steve

 

[zoomzoom]

The car is 2001 Audi S4 2.7L Twin Turbo V6 with oil coolant heat exchange element and 7qt sump capacity.

Heat exchanger helps oil reach 90C faster when car is cold and it cools oil down when car is driven hard since coolant temperature remains 90C

 

[Gary Allan]

Can you plot the indicated PSI/bar on the same graph?

 

[AEHaas]

Ferrari data example:

For a 40 wt oil at operating temperature:
The oil is thicker, has more internal resistance and therefore requires more pressure to get the same flow.
RPM....Pressure..Flow
1,000......30 PSI....1
2,000......60 PSI....2
4,000....120 PSI....4 The maximum flow because of the oil pop off valve at 90 PSI will be 3
8,000....240 PSI....8

Cold engine showing very high pressures because of the thickened oil at startup:
For a 40 wt oil at 75 F at startup:
The oil is thicker, has more internal resistance and therefore requires more pressure to get the same flow.
RPM....Pressure..Flow
1,000......60 PSI....1
2,000....120 PSI....2 The maximum flow because of the oil pop off valve at 90 PSI will be 1.5
4,000....240 PSI....4
8,000....480 PSI....8

An oil that is thicker at start up will hit the pop off pressure sooner. It will have a decreased flow. It will therefore pick up less heat as it takes longer to cycle all the oil through the engine.

Chemically thick or thin oil has the same specific heat so there is no difference in heat capacity per say.

aehaas

 

[zoomzoom]

Very interesting stuff AEHass..

So on the cold morning with temp below 32F as soon as we get going pop of valve will open due to the oil thicknes and high pressure...

With thicker oil (BC in my case) pop off valve will stay open longer then with GC(thinner oil) thus letting GC warm up faster since more of it is flowing trough the engine..

Makes me wonder looking at my data at what point in time oil is warm enough that pop off valve is not open any more?

What good is the extra protection of 40wt oil when at higher rpm not enough can flow to the engine!!

Gary I am not sure if I can measure(log) my oil presure..I will check on that..

 

[Gary Allan]

That would integrate your other questions. If we see how long the pressure antenuates at peak, we should be able to see some phase relationship between the heating process. It won't be perfect, but will give us just a little bit more data to expand upon in theory. That is, we will extend our assumptions further with more real and inferential data.

 

[AEHaas]

If the thinner oil is taking some more heat off the engine then the coolant should perhaps warm up slower. Is this the case?

aehaas

 

[Gary Allan]

Good question. I've wondered this myself. I would think that there would be a marginal slowing of the coolant warming up ..since you're effectively expanding that which it must heat. OTOH, if it was all that much, the oil wouldn't lag the coolant by as much time and would track it more closely.

Funny you should ask this. I'm going to add multiple heat exchangers to see how fast I can get the oil to temp. I wondered if I'll just end up delaying the coolant from reaching the threshold for getting out of fuel enrichment

I'm starting off with two of these since they're the easiest to install in the heater circuit:

 

[zoomzoom]

I will plot the coolant temps with two different oils to see if there is difference as how fast it gets to 90C..

hmmm..however with coolant there is another variable...T-stat...I think it opens at 80ish, not sure but I will check...so lets look at time it takes to get to 80C...

 

[bulwnkl]

aehass, were those oil pressure and flow data derived or measured?

 

[AEHaas]

Derivered, but close to the actual value. Use the flow rate of 1 to represent whatever your system flow rate actually produces. Then 2 times the flow rate would be correct if you double the RPM. In actuality it is not fully true as there are losses.

In any case, the flow rate is maximized as the pop off pressure is reached. Again this is not exact either, as the actual pressure and flow rate increases slightly as the RPM goes up.

But for demonstrative purposes the numbers are correct.

aehaas

 

[Gary Allan]

What would really clinch this is if you went real radical on the visc. I don't really expect anyone except someone like me to do this sorta thing. You would go with 5w-20 ..then go to 20w-50 on like days. That should step on most of the variables in ambient temp and event length/duty to make them non-factors.