2004 XJR

There is an annoying rattle that emanates from the driver-side dash. It has done this since I purchased the car 2 years ago, so there is no repair etc. that I can link it to. I have provided a video below/attached. I initially thought something was loose behind the dash, but given that (1) it persists when driving straight and at a constant speed and (2) it goes away when the car is warm, I suspect it may have something to do with the coolant. Air in the heater core? For what it’s worth, the previous owner said he had the coolant flushed, and my heater performs poorly. Thank you!

- Rattle only happens when the car is cold. It goes away when the car is at temp.
- Rattle persists even when driving straight at a constant speed
- Bumps in the road exacerbate the rattle
- Rattle stops when the car is stopped, e.g., at a stop sign
- Performance is not impacted
- Previous owner flushed the coolant, and the heater does not provide a lot of heat

 

Are you sure that rattle is coming from the interior? Almost sounds like something coming from the engine bay.

My initial thought about the weak heat is that the previous owner likely had the coolant flushed to try to resolve the heating issue, rather than the other way around. Assuming your thermostat is working correctly and the gauge eventually hits the middle, my first instinct would be to check the auxiliary coolant pump as they are known to fail on these cars and help significantly with cabin heating.

 

The first thing I would do is to do a further flush of the system to see whether there really is no air in the system anymore. Even if the rattleis not connected to the flushing, at least you will see whether the heater works better again, or whether the heater matrix needs replacing.
As you have an XJR, the flushing is a little bit more complicated than on the n/a engines, but it is really not such a big issue.

As the rattle stops when the car is sitting, it might also be a problem with the suspension. Sometimes, also there you get noises that are depending on temperature.

Best regards,

Thomas

 

Edit: the rattle does persist when the car is at temp, i.e., in the middle. However, it is not near as persistent (sometimes non-existent) as when the car is first driven.

I’ll add a coolant flush to my to-do list. I’ve been meaning to flush the heater core, so I might as well. While I am at it, I’ll reverse flush the heater core.

The aux coolant pump could be out, but I don’t believe that it is. A while back, I used a mechanic’s stethoscope and determined that it was running/whirring when the electrical systems were on (before the engine was started). I’ve read that it’s advised to replace it with a more puissant Bosch model with a modified bracket.

It’s possible that the rattle could be coming from the engine bay. The rattle sound is “hollow” which makes me think it’s coming from the dash. Additionally, it sounds “closer” that the engine bay. I’ll see if I can devise a way to investigate.

Again, I appreciate the input.

 

Flushing the heater core is integral part of the flushing process. There is no way to flush the heater core separately from the rest of the cooling circuit.

Best regards,

Thomas

 

See my post "front end rattle"

 

Thomas,
I may be wrong, but I thought one could isolate the heater core by disconnecting the two hoses that lead from the front passenger side of the engine bay through the firewall.

 

Meirion, I’ve got to put the air deflector back on following an oil change. I’ll check when I’m down there. A local shop that specializes in Jags, Land Rovers, BMWs, etc. did my brakes and recommended new front and rear control arms.

 

My understanding of "flushing" is mainly to get rid of air trapped in the cooling circuit. In this context, it would not make any sense to disconnect the heater hoses. The heater matrix is integral part of the cooling system. By disconnecting and reconnecting the hoses you will introduce air again that will circulate through the whole cooling circuit.

If by "flushing" you mean to try to see whether there is some debris in the heater matrix that you can get rid of, then yes, you can do it the way you propose.

But after reconnecting the hoses again, you need to flush the whole system according to the workshop manual to get rid of air trapped within.

Best regards,

Thomas

 

Couple tips:

- Your XJR has two elec coolant pumps; one is for SC circuit; the other heater circuit. Common to retrofit SC pump with Bosch E55 pump, but your heater pump not. Look at aux pump parts diagram to find location. V common failure; not hard or expensive to fix. Avoid Chinese replacement pumps

- Dash rattle when cold - yeah; mine does also; below freezing; first couple miles. Believe cold plastic shrinks a bit... Fix your hearing; it'll warm up faster ; )

 

Having watched your video and read the responses thus far, I wondered if you had had any success in identifying and rectified the noise. I have the same issue.

Thanks in advance.

 

I appreciate your response. I have not looked into it. It seems like it went away for a while and has only recently returned…or maybe I got used to it. It’s not a pervasive problem. Under what circumstances do you notice it? I can’t tell if it is coming from inside the dash or underneath the hood. My car has a conversion kit on the suspension. Does yours? Does your heater work well? Random, I know.

I am chasing another lead, and I will let you know if I learn anything.

 

Thanks so much for your reply.

It generally occurs in the first 5 minutes after a cold start, but on occasion it has reemerged later on a long drive. I'll take a video of it soon, but to me it sounds exactly like your issue.

I've still got air suspension. Is your suspension conversion to coilovers? If so, that probably rules out the noise being related to the air suspension such as the compressor.

The heating doesn't seem to be affected, although I can't say that I've paid particular attention to it - I'll monitor that.

Thanks again. If your learn anything new it would be great to hear about it.

 

I have a coil-over conversion.

I’ve updated my inquiry on Reddit - general auto mechanic forum - to include your input. I’ll let you know.