Hello Jaguar Fam,
I have a problem. I have a 2000 S type 4.0 v8 and I just replaced the head gaskets( yes I had the heads pressure check and milled and they are fine), new timing chains and tensioners, new water pump and thermostat, and new expansion tank. But my car is still running hot. If I let it warm up for about 15-20 min befor I drive it it won't run hot but if I hop right in it it runs hot. Any idea what my problem is?

 

R U sure it's hot, or pretending to B hot? Check coolant temp. with manual thermometer, plus re-check work performed along with purging air from coolant circuit.

 

Yea it was hot and boiling and Ive bleed the system twice . Im thinking that the new thermostat is bad going to buy another today to see if that helps cause when it doesn't run hot the heater will get cool then back to normal. but when it runs hot the heater stays hot.

 

Yep, sure does sound like the thermostat. Keep us posted after install.

 

I installed the new thermostat and it did good. Jumped in on cold start and drove about 15 miles no problems. I did discover a leak though, My expansion tank cap is the culprit going to get a new one.

 

Awesome! Good find on your part for thermostat.

 

I'm still having problems with my s type running hot it will runn forever in the driveway but runs hot if you drive it it has new head gaskets the heads were pressure checked and milled, new water pump and thermostat ne exspansion tank new tank cap bled the system until a steady stream flowed from bleeder and yes the heater was on full blast. Could it b the water pump old one had meatal impeler new one had plastic?Can someone please help almost at wits end with this car!

 

Are you sure all the hoses are connected correctly?

 

yea they are correct even double checked with a diagram

 

I read some where that the waterpump with the plastic impeller can sometime not pump the water correctly guess my next step is to take it off and swap it with the old on that has the metal impeller.

 

make sure your cooling fans are working. put a block tester on it to see if the combustion is leaking in to the coolant. Don't let it get to the boiling point.

 

the fan works bot it did boil on me twice stopped immediately when it did I have not tried the block tester but I did pull the plugs and look in each cylinder and there was no coolant.

 

i am not a mechanic but i remember something about the transmission being cooled by pipes that run through the radiator - im thinking if the car only runs hot when you drive it from cold but doesnt when you run it for 20 minutes at idle that maybe your transmission fluid is low ( it expands when heated doesnt it?) if the transmission fluid is low then the transmission might run hot until the fluid level rises which might result in a higher than normal running temp but not at idle when the transmission isnt under load.

i seem to remember that one of the members here found his thermostat had been put in upside down by his mechanic which might effect the running temperature.

there is always the possibility that your second replacement thermostat is also faulty.

if your vehicle has the electric handbrake could this be dragging slightly ?

just a few thoughts.

hope you sought things out soon.

 

I thnk you might be on to somthing because when I drive it it will start lurching right before it runs hot.butwhen I drive it and it doesnt run hot it won't lurch. I let it idle for about an hour befor I drove it today and it only ran hot when I drove it.

 

worth investigating then ;-)

 

My first move would be a block tester. Defective Tstat is rare.

 

Maybe you should post a picture of the connections to the expansion tank anyways. It's a known boo-boo area. Especially as you are suspecting the cap.

 

Some additional info. Afeter I replaced the headgaskets and timing chain and tensioner I bled the system and drove it about a hundred miles befor i had any problems. Another bit of info is that when it first tries to run hot it lurches but does not lose power then the needle starts to creep up but it will start to go back down. It wil go back to normal if I drve a ways but if I have to stop at a light or stop sigh I'm in trouble.

 

Oh boy can someone a tech or some one who knows help me out so far on the drivers side all cylynders dont leak through the expansion tank but number 4 on the drivers side seems to leake through the oil cap (I know bads news) going to check the passenger side now

 

correction nuber 3 on the drivers side