I have a 2003 XJ8 I drained the engine coolant to change it. I filled the system through the cap near firewall. Let it set for couple of minutes...topped it off. Started it up...turnd all ac and heat off...held rpms at 1500 till cooling fan kicked on. Then turned ac on high and turned temp to HIGH...LET IDLE TILL ALL HEAT CAME OUT VENTS. Shut it all down...topped off coolant...replaced cap. Now it will run fine...no water in oil....no white smoke out exhaust...all is fine....temp gauge comes up to half...run about 5 to 10 minutes longer and temp needle starts creeping up...at about 3/4 up if I turn on ac or heat the needle drops back to half instantly. Cooling fans run when key is off till they automatically shut off....please help....whats the problem...is there air still in it...am I doing something wrong? Help

 

Probably still air. Try squeezing and releasing the upper radiator hose repeatedly with the pressure cap off. called burping the system. It can be difficult to get the air out.

 

As i drive it the temp needle goes bouncing...then to hot...and I shut it off...cause it is hot...not needle pegged...is there a bleeder on the system or no?

 

As mentioned, you should be able to burp the system without too many problems.

If you did not do it, just replace the thermostat as well, they are known to stick over time.
Mine did so soon after changing the coolant.
They are cheap.

 

I was thinkn the same...replace thermostat. I have no foam in oil and no white smoke out tailpipe....is it safe to say headgasket is ok? Its just in back of my head...thanks in advance.

 

You should be ok, but dont gamble by driving it more.

 

By saying that there is no white smoke or water in oil now .... that there was before you changed the coolant ?

 

IF it was running at a stable temperature BEFORE you drained and refilled the coolant, it will either be air in the system (the likely cause of erratic temperature) or the most extraordinary coincidence of a failed thermostat/water pump.

Graham

 

The coolant was never dirty...or the oil...nothing...I was just trying to get some maintenance done....now cant get it right...cant BURP the air out...temp needle never did this till I tried doing some maintenance....hmmmmmm

 

At the risk of creating a leak, or breaking the plastic, you can remove the cap on the thermostat tower and be sure there is no air.
It is the 2nd highest point in the N/A cooling system.
Replacing that tower for an alloy one, replacing the plastic cross over pipe in front of it, and replacing the thermostat are then good precautionary matters.

 

Whats the best way to make sure headgasket is good? A forsure way....

 

Combustion gas leak tester, for example: https://www.walmart.com/ip/COMBUSTIO...IESEL/16550935

 

You can find a host of youtube video’s on this topic that give you several practical options that you can do/check yourself


if all fails, then at some point in time you will have to do a proper pressure leak test. It requires some test equipement,

Good luck

Jeroen

 

You can borrow a pressure test kit from autozone and other stores.

 

 

I used orange...thats what was in it....was that correct?

 

 

Off chance: did you remove the black plastic pipes that run from the coolant tank by the firewall: one house runs to the radiator, the other to a sure tank behind the left fender. These are suppose to be crossed; often as not, people run them direct vice cross them over. The pipe at the front of the tank goes to the radiator, the pipe on the side crosses over and goes to the fender surge tank. When these are installed wrong you get blow by and overheating.

Second choice: stuck thermostat. Third choice: disconnected fan switch.

 

So here is the latest...I started all over...drained all coolant. Added 50 50 mixture to fill. Started it up...topped it off..put cap on. Held rpm at 1500 till fans came on with all climate control off. Once fans came on...I turned ac on high HOT. HAVE LOTS OF HEAT OUT VENTS. Shut down car. Let sit for 25 min. Took cap off topped it off again. Replaced cap. Started it up....ran in driveway for 30 min...fans came on...shut off...needle never went passed half. Take it for a drive...get about 5 miles down road...I turn all climate control off...slowly temp goes above half. As soon as I turn ac on with Hot temp controls the needle drops back to normal. I turn around head home. Get home and now its leaking coolant near crankshaft pulley. I believe its leaking out of waterpump...if thats near the top...below radiator hoses. Does anybody think thats my entire problem? Water pump os bad..and now leaking? Im so confused....

 

Do you have a way to pressure check the cooling system with a tester...or maybe rent one...that is what I had to do to find my leak. Had to get the front up in the air and take off all underbody covers and anything on top not cooling related...pressurized the system and found it from the bottom..different car of course but principle the same...and did it while cooling at ambient so I could move hoses around and get a good look...a lot of work but it was the only way for me at that point