I have a 1999 XJR with approximately 80,000 miles which I bought earlier this year. I have experienced two problems while driving on the motorway.

1. At approximately 65mph+, the cabin will vibrate intermittently - it occurs during acceleration, while holding a steady speed, and while decelerating. The vibration tends to worsen at higher speeds. I have had the wheels balanced, but the problem persists.

2. The engine coolant temperature is very low while running at motorway speeds: it is generally on the border with the blue segment. On one occasion, it fell right to the bottom and an orange warning light and "Restricted Performance" appeared.

Has anyone experienced either or both of these problems, and if so what is the solution?

Many thanks for any assistance.

 

Intermittent vibration is a tough one. Check the rubber jurid coupling in the driveshaft.

Change the thermostat.

 

Many thanks for your prompt response. That's very helpful.

I should have mentioned that the engine coolant temperature is normal during stop/start driving (i.e. in town). Is that still indicative of an issue with the thermostat?

 

That's when there is little airflow through the radiator. I'm wondering if you even have a thermostat.

 

+1 on the driveshaft coupler. Even though the car has relatively low mileage, it's also the age of these cars that reek havoc on the materials hence the rubber couplers are no longer pliable and turn hard as a rock. Or you may also have a coupler just coming apart.

Sounds like your thermostat is stuck open.

 

It should help if you mention where you are located.
Big difference if arctic or tropical temperature air flows through radiator .
Does your interior heat also drop down?

 

I'm in the UK, and it's a little chilly at the moment. That may explain why the temperature is so much lower. Yes, the interior temperature is also lower.

Thanks for the very helpful replies. I'll ask a garage to have a look at these.

 

The thermostat is intended to have a rubber gasket around it, to get a good seal. I had a problem where the thermostat was working OK, but the gasket was not installed, so enough water was leaking past to make warm up very slow, and in cold weather on the highway the engine would start cooling down.

 

My R type is very sensitive to out of round or out of balance tire issues.

Get a "Hunter Road Force" balance job done by someone who knows how to do everything the machine tells them to do.

+1 on the thermostat, either you don't have one, or it is stuck open.
Vector

 

The vibration appears to have been caused by incorrect wheel balancing after all - that is now fixed. A new thermostat has, I think, solved the temperature issue.

Thanks again for the replies.

 

sometimes it is the simple things . . . . . .