I am losing coolant in my 2013 XJL 5 liter supercharged. There are no visible leaks, it is not losing a lot of coolant but I am topping it off every few weeks. Took it to my mechanic and he run pressure tests and believes it is a head gasket. Has anyone run into this problem? How big of a job to repair?

 

A head gasket is a fairly large job. The supercharger and everything around the head has to come off. If that is the problem make them replace all the plastic tubes in that area as well. A bad head gasket will look like a slight loss of pressure, about 2 PSI, and then will hold steady from then on. Your filling the cylinder with antifreeze and when it fills up no more pressure will be lost. A slow steady drop that doesn't stop is a leak somewhere and keep looking for a puddle. If it doesn't drop and doesn't leak anywhere replace the radiator cap. I've had head gaskets done before for about $1,200 on a Pontiac v6. At least double that for a supercharged Jaguar I would suspect. That is if they take it to a machine shop and have the head shaved to be flat again. Aluminum warps and that's why you get a leak. Getting on it a lot will stress the aluminum and over time will blow a gasket. Depending on the mileage you might want to have them look at the timing chain guides as well.

 

Did your mechanic inspect the water pump?

 

An other vote for the water pump. The 5.0L rarely loses a head gasket.
Maybe test the coolant for combustion gases first?
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I had a head gasket failure at approximately 47,000 miles on my 5.0L SC which, fortunately, was covered under the new car warranty. It was at the dealership for about a month and they did send the head out to be milled. Has been fine since the repair.

Dwayne

 

Put the car on a lift and remove the aero pans. Look at the top of your transmission bell housing. If you see green coolant drippings, you need to replace your rear crossover tube. A pain, but better than replacing head gaskets.

 

Where's the OP? Why no updates in over a month?