I have a 2006 XJ8 (X350) that overheated on a long trip. It was through ‘bug country’ in Florida’s north. (lovebugs) My windshield literally needed to be scraped off as they were more than washers could handle. There was a lot of stop & go through what was supposedly the ‘shortest/fastest’ route.

After heading back south, I decided to veer over to the interstate. (Guessing less bugs!) My poor old XJ has had a hard life in the hot south. The touch screen is ‘sunburnt’ & lately won’t even light up unless warm enough! (And side controls don’t work until on)

I had passengers and because cool temps outside couldn’t shut off a/c. (Much warmer in South vs North where we currently were.) When I first got car didn’t realize air cleaner unlatched in one corner. Car occasionally got hot & (TSB bulletin describes) fault where a/c quits, Speedo & gauges quit (Except gas) and is hard to start (TSB claims ‘won’t start’ but I found out engine wire housing comes ‘slightly loose’ & pressure solves it.)

Anyway I thought maybe I could ‘recreate’ that to cause a/c to be off! In retrospect I’m guessing lovebugs covered RADIATOR as much as windshield & bumper (I had scraped the latter two & ignorance skipped cleaning off the radiator.) so the car overheated & developed leak (Seemingly) at upper rad hose. It was Sunday & needed to drive several hundred miles so tried using ‘bar’s leaks’ just to make it home. Battery light was coming on intermittently too.

Made it home only adding some (watered down) coolant. (Used a lot refilling since had overheated.) Ordered hose & reservoir just in case (Had reservoir leak on previous Jag). Battery died & recharged & died again. Tested bad so replaced. Hoping just V-Belt damaged from overheating so bought that.

Mechanic suggested change thermostat too but Rockauto sent ‘wrong’ so couldn’t use. (Late model 06 are like 07) Alternator must’ve been ruined from coolant too as shop said bad. After pickup still got ‘coolant low’ message. Shop said because still need new thermostat. Got new thermostat assembly (All plastic so it’s recommended to replace all.)

Picked up car (Billing 4-5 hours for removal & replacement?!?) And after idling 5 mins waiting for someone and as turned onto highway say temp gauge climbing so turned heat high/fan low & temp was dropping so decided to shop at store & let car cool. I guess aluminum blocks cool fast as in 1/2 hour normal but ‘coolant low’ light on. Checked w/engine on & looked ‘fine!’

Went back to shop. Mechanic claimed he let car idle 2 hours. What or WHY would car idle normal (except a/c not cooling properly) and begin to overheat when put in drive?!? ‘Coolant Low’ only comes on if car is running for a while! OR at low speeds.

Bad reservoir sensor?!? I determined engine fan no longer functional (Could coolant have damaged it too?!?) so that’s why getting hotter idling and driving low speeds. I just don’t understand coolant reservoir sensor ‘behavior.’

I’m ordering a new fan soon but will have shop ‘test’ it first. Anyone have any ideas about reservoir?!? New reservoir, new upper hose, new thermostat assembly includes temp sensor. New V-belt, alternator & battery.

Thought Bar’s Leaks could be issue but mechanic claims flushed twice. They didn’t use orange OAT but universal green. (There ARE still a few visible copper ‘flakes’ in coolant.)