^^id start with coolant levels also. Even with my valley leak I never had any fluctuations; this includes heavy spirited driving and never once has it passed centre.

 

Not good, to be frank with you, I never ever seen coolant temp change, but with that said, there's not many things to look after.

1) Get the compression done - (leaking compression, specifically into cooling tract may result in over-pressurizing the cooling system, blowing coolant out and then overheating)
2) Hanging Thermostat - Not sure how many crazy ISF has, but in good'ole Scoobies and Evo's there was only one, stop or restrict circulation of coolant. I always had a fully open at hand, mocked up from original without the thermostat part. Happens rarely, very even.
3) Burping the System - Usually consists of running car through few hot> cycles and having the radiator cap open letting all the air out, can't go wrong with https://www.amazon.com/Lisle-24680-S...Burping+Funnel as water expands creating pressure, higher pressure, the higher the boiling point and more velocity. After you stop seeing bubbles coming out of the funnel then you can cap it and close the top radiator cap.

I'd really go with 3 and 1 first, I never ran into hanging thermostat, going full open was usually just a patch.

Also some questions to ask, when are you overheating (traffic, city driving, highway, all)?
Does it ever go 1 bar above mid?
Do you hear radiator fans kick in?
Does the oil temp climb at anytime (besides track use)?

 

Unless your idea of normal driving is completely insane then the dealership is wrong and that is not normal, had mine in florida summers(95+ temps + humid) and colorado summers (easily 100+) and it never went above normal operating temp even under spirited driving. GL getting this sorted out, at least its under warranty.

 

I would find another mechanic and get another opinion.

 

I live in So. Cal and deal with triple digit temps (110°F) and my temp gauge has never gone beyond the normal temps even with "spirited" street driving

 

My coolant temps never went past the normal setting even when oil temps were one bar from maximum at a track weekend in 102F heat. Cap could be bad, valley plate could be leaking, o-rings from the coolant pump to the valley plate could be compromised, but any of these thing would be found on a basic cooling system pressure test.

Sounds like you need a better diagnostic tech on your issue as it is not even close to normal.

 

Bought my 2011 F in to get checked by Dealer waited week to have the master tech check car, symptoms back in December 2015 Topped off the coolant because it was low by June 2016 it was back to low again top it off one more time in june now nearly two months later lost close to inch of coolant. My Car currently has 69760 miles factory warranty will cover any necessary repairs. I'm having them check the transfer case gear oil as well as the tranny oil while it's there, I do my own oil changes and will be changing the spark plugs when I get the car back. I've already had all recalls done on the car which were the wiper blade nut abd fan bolt replaced. My car is not currently a candidate for the elf recall. I hope they find the valley plate leak or any leak that may be causing it to lose coolant while the car is still under warranty I actually wanted to find something. I asked for pressure test as well as visual inspection when I spoke to the Master tech he said he was aware of issues with the LS 460 Valley plate leak that it was caused by the sealant degrading. To date He's only seen one ISF with Valley plate leaks that he would use his camera to do a visual inspection.

 

Is it using coolant ?? do the fans cut in and bring the temp back to normal check temp with a external heat gun could be a crook senser, good luck and let us know what you find

 

UPDATE: Turns out there was a valley plate leak causing my car to run hot, i purchased my car certified pre-owned so the whole repair process and rental car were covered by warranty, got the car back today and drove it quite a bit to see if the temp would fluctuate and after about an hour of driving the temp gauge didn't budge from the normal level even once. I'm happy to have my IS F back and I look forward to owning it for years to come!

 

That's great to hear. The valley plate leak seems to be occurring more commonly.

 

Good to hear and thank you for coming back and letting us know what the problem was and how it was fixed.

 

Interestingly enough i just had my 08 with 75k miles serviced for a automatic transmission flush and my service advisor mentioned the valley plate is commin for leaks and its hard to detect. He had his tech check it just incase and im all good. Defined something to look out for continuously and the oil change service interval.