Oil cooler and oil temp at 250F - what's too hot for high-speed cruising / track use?

[thefleshrocket]

I have an '11 S4 6MT, dual pulley with an APR tune, upgraded heat exchanger and intercooler pump. The chassis has 137K on it; the engine was replaced with a 65K unit about 15K miles ago, so it has around 80K on it.

When cruising down the interstate at 85-90mph on an 80-degree day, oil temp sits around 240F. Cruising at 100-110mph results in the oil temp being around 250F. Prior to owning this '11, I had a '15 S4, and it sat between 215-225 at interstate speeds. My GF's '15 A4's oil temp behavior is similar, riding around 215-225 at high-speed cruise. To the best of my knowledge, the oil cooling system is the same from '10 through '16, which leads me to think that something is wrong with the oil cooling system in my '11.

From what I can tell, the oil cooler system is thermostatically controlled. Maybe that thermostat is stuck closed. Is the thermostat part of the oil cooler assembly? IE, if I bought this kit, would it likely address the problem? https://www.ecstuning.com/b-assemble...-06e117021gkt/

My main concern is that if my car's oil temp is at 250F during high-speed cruising, how hot will it get if I do a track day with it? And how hot is too hot for the oil? 270F? 280?

[SwankPeRFection]

I’d like to know where in Illinois you cruse at 110. Lol. That said, on mine, when doing pulls, it’ll climb into the 230’s and if cruising normal speeds 70ish or so, it’ll drop to 220’s. Generally I’m in the 220’s normally. Super high stuff can hit 250ish.

How are you reading the oil temp? Did you enable your track timer or are you doing it via another readout/gauge setup? The temps I spoke of are coming off the factory track timer on mine, which is basically the stock oil level/temp sensor.

Since you had your engine replaced, did you do that yourself or someone else did the work? If you didn’t do the work or aren’t sure, have you looked to see and make sure all factory oil cooler connections were put back how they should have been. There’s always the possibility that something wasn’t routed correctly and you could be either reversing the flow or putting in flow from other lines going to your IC heat exchanger or some other stupid shit. It would be hard to screw that up if you did a proper replacement, but it wouldn’t be the first time I’ve heard of someone deciding to route something different when upgrading parts and it causes problems.

Also, remember that these engines tend to run a little hot for the oil side of things. Audi did this kind of on purpose. Technically 230’s in right where you want to be with oil and operating temp for it.

[thefleshrocket]

I usually cruise the interstate at 90-95mph, and if someone passes me, I'll tail them. A few days ago, I followed a couple cars going 100-110.

I am reading oil temp via the lap timer.

The engine replacement was done by the PO, or rather, by a shop for the PO. The works seems solid as there haven't been any issues related to the swap in the 10K miles I've owned the car.

Rather than eyeballing or R&Ring stuff, I'd prefer to just replace anything that could be bad and causing high oil temps. Is the oil cooler thermostat external to the oil cooler (something that I would need to replace in addition to the oil cooler itself) or inside the oil cooler (so replacing the oil cooler would address the thermostat too)?

[SwankPeRFection]

I don’t believe the oil cooler is thermostated at all. It’s one that’s channeled right off the oil pan and has both oil and coolant flowing through it. These kinds do two thing, help in bringing the oil up to temp as your engine coolant warms up quicker than the oil generally and as a cooler once the oil is at a higher temp than the coolant. That said, if the coolant lines coming off of it have been misrouted and are plumbing in coolant from a hotter source, it could be introducing a heating affect that’s not there in stock form. It’s been a while since I’ve looked at those lines (when I did my mounts) but I don’t think you can mess that up too much.

You can try replacing it but I can’t guarantee that’ll fix the issue unless you’ve got something like a partially clogged core in yours where coolant may not be flowing as well through it. They don’t generally fail and if they do, it’s evident with coolant/oil mixing and other problems surrounding that. I’d get under the car and check things out and see what you’re working with. If you do need to replace it, it’s easy as it’s two hose barbs for the coolant lines and small screws around the perimeter of it, but you will need some small wobble extensions and flex sockets to get to the tight placed ones at the top and corners of it. Nothing too bad though. Make sure you have a new gasket however.

[SwankPeRFection]

I tied to find you a line diagram for the stock cooler, but I can’t seem to find one and 034’s pics in their engine mount guide that had this info as well aren’t working. They are cached on Google’s image search but don’t display if linked. I’d make sure the lines weren’t accidentally reversed for the coolant on it.

That said, if you end up wanting to do an aftermarket cooler for it Hel Performance makes one and Forge used to too. Just be careful to not overcool your oil while on the street. The idea of a cooler during racing is nice to have, but overcooling is also a bad thing to have as well.

[destrux]

The engine coolant warms faster than the oil, so there is no oil thermostat on the oil cooler. The oil temp is brought up as quickly as possible to operating temp by the hot coolant and then the coolant temp being regulated by the thermostat is what regulates the oil temp, the oil cooler doing it's best effort to keep the oil at the same temperature the coolant is at.

If your oil temp is elevated then suspect oil flow issues. Incorrect oil weight, oil contamination with other fluids, oil filter restricted, or oil cooler is restricted. Also consider that if your thermostat or other cooling system part is failing and your coolant temp is elevated that it will elevate the oil temp to match.

[thefleshrocket]

The engine coolant warms faster than the oil, so there is no oil thermostat on the oil cooler. The oil temp is brought up as quickly as possible to operating temp by the hot coolant and then the coolant temp being regulated by the thermostat is what regulates the oil temp, the oil cooler doing it's best effort to keep the oil at the same temperature the coolant is at.
If your oil temp is elevated then suspect oil flow issues. Incorrect oil weight, oil contamination with other fluids, oil filter restricted, or oil cooler is restricted. Also consider that if your thermostat or other cooling system part is failing and your coolant temp is elevated that it will elevate the oil temp to match.

Thanks for the suggestions. I've used Mobil1 5W40 and 5W50 with seemingly identical temps. No oil contamination--has been sampled and come back good. Oil filter has been replaced with no effect. I also just replaced the oil cooler over the weekend. Coolant temp is in the 203-207F range during normal driving.

[thefleshrocket]

Did a track day yesterday at Gateway near St. Louis. Four 20-minute sessions in 85F ambient. Coolant hovered around 205F. Oil crept up to 257F and didn't go any higher (whenever I glanced down at it). Charge cooler temp spiked into the low 180s on the front straight but immediately dropped back to the 130s by turn 2. I was expecting to see the oil get to 275F or beyond, so I'm happy with it having stayed just a hair higher than the 250F it sits at during high-speed interstate cruise.