Hey guys,
Last week, my XK8 started taking forever to reach operating temperature. Once it gets there, all is well. With the cold weather here, I can turn the car on and let it idle for 15 minutes to get heat, but I don't like letting it idle that long. I had replaced the thermo and the housing a few years back and it always functioned properly. Before I tear into it again, I'm wondering if there could be any reason other than the thermo that would suddenly cause this to happen. Thanks!

 

The thermostat is the most likely cause and I would start there.

 

Your electrical heat pump may have slowed or failed.

 

Thanks. I've never been clear on what the heat pump is. Can you explain a bit?

 

Although Thermostat is the most likely cause, a faulty ECTS (Engine Coolant Temperature Sensor) sending an invalid signal to the ECM (Engine Control Module) could also cause apparent slow warm up.

Graham

 

Don't discount a basic heater core cleanup. Best I can figure, the dexcool forms a form of film that sort of prevents good heat transfer, it's not about real obstruction. I went from having the car take many miles to get warm to getting some heat within a half mile, and hot air coming out the vents with the needle barely halfway to operating temperature. You have to set the expansion tank aside for access, empty it with a turkey baster, then reach out and disconnect the 2 hoses to the heater core (long reach hose pliers a must here). Then hook up a short clear tube with a garden hose adapter on one side and the rest of the clear tube on the other side as a drain. Drain into a container for later inspection, but don't expect anything dramatic (I had some sort of "sea foam" floating on mine, no hard debris). Do forward and then reverse flush for good measure. Using a bit of proper radiator cleaner does not hurt (Prestone, etc.). Hose and adapters should set you back less than $20. Then use gravity/siphon to clear the water from the core and hook everything back up. Then refill with dexcool as usual. There are many videos online that show this basic procedure really works. Definitely worked for me...

 

Graham, she's definitely slow to warm up as evidenced by the heater putting out appropriately cold/cool air until operating temps are reached (verified by the RealGuage). Then all is normal.

 

Fmertz, I hope that's not the case as I don't have a garage (next house definitely will!) and it is too cold to be messing around outdoors with coolant now. I'm concluding it's the thermo since it happened suddenly one morning, not gradually. And the heat rises in lockstep with the Real Gauge rising. I will probably live with it until we get a day warm enough to work on it. Of course, I'm hoping the Jaguar fairy will one day suddenly pop open the thermostat for me.

 

Thanks, all!

 

this comment has nothing to do with your issue, but there is NO good reason to let a car idle until it's fully warmed up.

Yes. by all means, let it idle for 60 seconds before driving off. And once under way don't give it full throttle, i.e a heavy load, until the engine's oil is fully warmed up. But the fastest way to to warm up a cold engine is to drive it (like a sane person) after the 1st minute of idling.

A little work being done by the engine will speed up the warming significantly vs. just idling in the driveway, and won't harm anything. When idling the cars lubrication system is barely providing adequate protection to the moving parts. Every respectable automotive engineer will tell you most wear occurs when the engine, and the engine's oil, is cold, and just idling. A quick warm up by actually driving the car is reducing the time the engine is running cold, and thereby is also reducing the period in which most wear occurs.

and you can take that to the bank.

Z.

 

Then I think component failure is much more likely than electronic glitch. The latter would keep the rpm up with rich mixture ("cold" start settings) for longer than normal.

Graham

 

Zray, of course, I agree. The only time I'd let it idle a short while is when we hit the low-teens and single-digits and a cold car is nearly unbearable.

 

^^^^^ nearly is the key word

decades ago, in the hippie years, I had to drive a car about 200 miles one WINTER night with no heater and a shot out side window (don't ask, statute of limitations, and all that). I was pretty miserable until I found a paint stirring stick I could put between my teeth to keep them from chattering together.

If I recall correctly, that was the same winter I couldn't pay the gas bill and they turned it off. Man, cold showers in 20 degree F weather will give a person incentive to get off their a** and get a job.

Z

 

As I read the posts in this thread, I saw two issues discussed. One problem was the engine slow to warm to operating temperature, and the other was a lack of heat in the passenger cabin. These problems are related to the point that the engine needs to warm up to provide heat to the heater core for heat in the passenger cabin but they are otherwise separate issues. If an engine is slow to come up to operating temperature, the most probable cause is the thermostat being stuck open, allowing coolant to be circulated through the radiator, slowing and limiting the increase in coolant temperature in the engine. The function of the thermostat is to separate the engine coolant from the radiator coolant to allow the engine to warm up, then to regulate the engine temperature by opening enough to circulate coolant through the radiator. Lack of heat in the passenger cabin with a properly warm engine is either a problem with coolant flow such as a clogged heater core or an airflow problem.

If this is not a thermostat problem, I'm sure I'm not the only one interested in what it is. Keep us posted.

 

Greg,
There's no shortage of heat... once the engine reaches operating temps. Thermostat is the problem, not the heater.