Does anyone have an opinion on installing the German Wahler thermostat, which has an opening temp of 88C (190F), which is 10C lower than OEM (98C or 208F) based on my brief web search.

Can anyone confirm OEM opening temp?

Would this confer less heat cycle strain on the cooling system during each warm-up?

 

The OEM thermostat for most F-Type engines typically opens around 98°C (208°F), so the Wahler 88°C unit is indeed lower. Using a cooler-opening thermostat can reduce heat cycles and may slightly lessen engine warm-up stress, but it could also affect optimal operating temperature, fuel efficiency, and cabin heating, so weigh the trade-offs carefully.

 

Are all Wahler thermostats 88C ?

 

Yes, it seems so, which makes it a compelling choice. It is also listed as an OEM alternative replacement.

I notice on first warm up the car goes to 220F then settles down to 190-200F when not in dynamic mode. In dynamic mode with the exhaust valves fully open it goes to 200F then settles down to 190-200F after first warm up.

I see no reason for the additional temperature spike when in non-dynamic mode. Anyone else notice this phenomenon? The thermostat is wired so must have some ECU control input going on to explain this.

 

'Traditional' thermostats are usually sticking closed initially, when the the temperature spikes like that. I've had new ones do that (not on the Jag).

Often the 'wired' aspect of a t-stat (or it's housing) is where the dash gauge receives its signal.

 

I wouldn't. The thermostat on these includes a heater control, basically the ECU can warm up the wax as needed to allow it to open earlier based on parameters in the ECU. Meaning it can open early if needed. (Those two wires with a single harness connected to the thermostat)

If you want more capacity in the cooling system, then you'd have to increase mass or the efficiency.

 

Dynamic most likely forces the thermostat open earlier. The way the PCM controlled ones work, they are mechanically set for say 230F, but the heating element can warm them up and open them earlier. So in normal mode they want max heating available from a cold start, and to warm the engine up as fast as possible for good emissions. Dynamic probably overrides this and keeps the t-stat open at it's earlier level for more room for performance use. Sustained full load would drive temps over the t-stat minimum anyway, but unless you are on a top speed track run that just isn't possible. Running the car 10 degrees cooler isn't going to have any noticeable effect, for good or bad, on a modern car. You do run the risk of the PCM flagging a fault temperature below desired if the t-stat opens too fast, but that's usually triggered below 160F.

 

@RoverJoe Thanks for the explanation about Dynamic mode - makes sense now.

Because much of the forum is dedicated to preventing overheating to avoid total engine loss, here are some other thoughts: The lower opening temp won't make the engine run cooler, just decrease the upper limit of the heat cycle after starting up. This is what many consider the main reason for the plastic coolant pipes deteriorating over time. Just a theory. There's no reason this engine should rise to 220-230F and risk overheating and head damage from regular driving after first start-up. There is also the possibility that parking the car at 220F and turning the engine off will lead to even higher temperatures in the head when the coolant system is no longer circulating.

Another potential issue is the temperature sensor possibly sensing the coolant coming out of the radiator (coolest) and not out of the block (hottest). I can’t say for certain that this is the case in the F-Type based on the cooling diagram, perhaps someone can confirm? Looks like there is a sensor in the rear heater pipe or near the power steering pulley:
https://www.jaguarforums.com/forum/a...581d1627244885

There’s a deep dive on several Porsche forums regarding this topic, with mention of pockets of coolant slowing down through certain low-flow areas of the block and heads. During spirited and/or high ambient temperature driving these coolant pockets may superheat past boiling then remix with cooler temperature coolant downstream (with normal temperature detected by the sensor). This results in oil separation/thinning and potential cylinder damage.
https://rennlist.com/forums/997-foru...e-scoring.html

 

Yes and no, in general the t-stat opens at say 190-200 degrees, and the fans come on around 210-220. So opening the T-stat sooner won't actually change the limit of how warm the engine gets, as the fan still controls that. A tune would be your best bet to bring the fan on sooner if keeping temp spikes down is the goal.

For reference on one of my cars that I tuned, I left the t-stat opening at 180 all the time, and brought the fan turn-on down from 220 to 205 for the first stage, and then ramped at 220 to full blast. OEM logic had the car hovering around 230 in normal conditions, and that car didn't have an actual temperature gauge, so the room between a warning and overheat damage was miniscule.

There is afterrun logic in the PCM for fans and aux water pumps to stay on and circulate things for a bit if the temps are high enough. There are multiple sensors, 3 in total I believe on that configuration, for the coolant. The car mainly uses the one at the cyl head outlet to make it's changes, but it looks at all of them for inferred temps on other things and many calcs. It also sees oil temperature, ambient and inlet air temp pre/post intercooler, it's a lot of info to use. It's not so simple as on/off anymore sadly.