I have a Jaguar 2017 XF 3.0 Premium with 40k miles. The cooling system sprung a leak in January and was rebuilt by a nondealer mechanic. This nondealer mechanic specializes in European vehicles and is well regarded. Seventh months later, I received a coolant low warning. Filled the coolant and watched it. And it continued to go down slowly. Took to the dealer and they identified a leaky hose that was replaced. They pointed out that when they drove the car, the coolant was bubbling. And they said that thermostat might be the issue because they suspected that the thermostat that had been replaced in January was not an original Jaguar part. I had them replace the thermostat and the coolant is continuing to bubble. The dealer is insistent that it is not the head gasket. There is no gas in the coolant or other signs of head gasket failure. They are now replacing the radiator which they say is not likely to be the culprit but they don’t know what else is the issue. They have told me that if the radiator replacement does not work, that means that the coolant blockage is in the engine block and the cost to fix it is prohibitive. I am shocked and dismayed. I would appreciate any advice about what to do.

 

Don't let them just go throwing expensive parts at it in hopes of finding the leak - that's what amateur shade-tree mechanics do. Thermostat was never the issue. You need to call them first thing Monday morning and tell them to stop what they are doing and just put everything back together because you're sending a tow truck to come get it. Then do your research and take it to somebody else in town who either knows what they are doing or isn't trying to scam you. There's tools that can pressurize the system cold. You could even get one at Harbor Fright and do this yourself. Pump up the system to (can't remember how high but its printed on the cap), take all the covers off and even remove some parts out of the way if necessary in order to see where the coolant is leaking from. Use a really bright LED flashlight, like Fenix or such. If its not obvious in half an hour of inspection with a bright light, next test is to remove the undertray, lay some clean paper under the car and leave the system pressurized all day, checking it about once an hour, maybe even leave it overnight if its a very slow leak. Almost guaranteed the paper will eventually be wet with a little orange stain in some spot. Follow the wet trail of the drips upwards to the source of the leak. They should have done all that. There's a whole bunch of parts in the cooling system that are actually very likely to be leaking at this age such as the front seal on the water pump, the reservoir itself or any of several tubes and connectors made out of PA-66 Nylon, a material which only lasts on average about ten years in a cooling system but if you live in a hot place like Texas, yes, its shorter.

But since you said the "system was rebuilt" seven months ago (I'm going to take that to mean they changed the water pump) and has been slowly leaking since, I'll wager its the funny o-rings at the back of the water pump. If they aren't lubed up when the water pump is installed, they'll roll over on themselves and not seal properly. Professional mechanics can tend to get in a hurry and forget or skip that critical little step,. Have you ever gotten a whiff of coolant smell when you get out of the car on a hot day?

 

Thank you so much for your reply. The system has been flushed multiple times and they believe that the coolant is not leaking. The coolant is bubbling and they are saying the temperature of the coolant is about 70 degrees warmer than it should be. They believe that there is a blockage somewhere...but they don't know where. Is your advice still the same? The car is being worked on by a Jaguar dealership. We don't know where else to take it in Houston.

 

I should also mention that i have been skeptical from the get-go, and told the dealer that i dont think its either the radiator or the thermostat. Have been in multiple convos with the manager and the shop foreman. Also the other well-reputed nondealer said they used Jaguar parts and did not. The dealer said there is nothing that can be done if it is not in the radiator. Have taken it to two dealers and two non-dealers and been very dissatisfied with all. I am not a mechanic. My options are to (a) try this and hope (replace radiator, where the dealer suspects the blockage is but arent sure); (b) take the car back and drive it till it dies; (c) start over with a fifth person (which will likely be a few more thousand bucks). I previously had a beemer and while the car had its issues, i loved the mechanic. I have no trust in anyone.

 

You described coolant levels going down so I just assumed you were describing a leak. Blockage is rare nowadays. Cars used to develop blockages from corrosion all the time but metalurgical and chemical technology has improved. I can't think of anything that would create a blockage on a car this age except for a "mistake" by somebody previously like pouring in a whole bottle of magic headgasket repair or filling it with ordinary tap water and running it that way for a long time. Did they try flushing the system? The other possibility might be installing a gasket incorrectly or using too much RTV. That might be harder to track down but still correctable.

 

Bubbles coming up from the coolant could be head gasket failure despite what they say. So here is a test - when the engine is stone-cold, is there pressure in the coolant jacket when you remove the pressure cap ?