Hello everyone,

It seems that part MJD4400BA (coolant expansion tank) is now NLA (no longer available) from Jaguar.

Earlier this year, my genuine tank failed by leaking at the seams. I replaced it with a Eurospare tank purchased from FCP Euro. The result: a “Low Coolant” warning despite the system being completely topped up.

I initially reused my original sensor — the warning persisted intermittently. I then replaced it with a brand-new genuine Jaguar sensor, but the issue remained. The problem appears to be a defective float mechanism inside the Eurospare tank.

I attempted to purchase another genuine tank from FCP Euro, but the following day I received an email stating it was back-ordered with no restock date. My credit card charge was reversed even though their site had shown the part as in stock.

Checking SNG Barratt, their website now lists the genuine part number as superseded by the same aftermarket reference, confirming that the OE tank is discontinued.

From what I can tell, all aftermarket versions currently available suffer from faulty floats or sensors.

I also reached out to Radtec about having an aluminum tank fabricated. They responded that they cannot replicate the sender/float mechanism, and that the tank’s shape would require a complex machined design, making it considerably more expensive.

So I’m wondering — has anyone here found a reliable aftermarket tank (any brand) that doesn’t suffer from float or sensor issues.

Any confirmed success stories or long-term fixes would be greatly appreciated.

 

I had to replace the coolant expansion tank (MJD4400AB) on my wife's 2006 XK8 in September 2017. I ordered it from rockauto.com and paid $58. It obviously was not OEM, but it still holds up today (probably because the car was no longer my wife's daily driver as of late October 2018)....

In March 2021 I decided to order another one as a spare, knowing that sooner or later I would need it. Same part number, same rockauto.com source, and the price had increased to $62. It sits on my garage shelf waiting its turn....

As you indicated, they all eventually leak either at the seam or the nozzles. If you can find one somewhere for your XKR, regardless of manufacturer, I would order at least two of them....

 

FWIW I purchased one for my XK8 from Amazon last month. So far it's been working fine.

 

I bought mine from RockAuto.com at least 5 years ago, the SKP brand, not the URO. It’s still working perfectly. It comes with the cap and the sensor. Currently on RockAuto for $38


Z

 

The Eurospare has not been working for me. I just checked rockauto and found that the SKP is available at $38. For that price, I don’t mind trying it out, especially given that you have had a good experience with it. I’m going to order one right now.

 

when I checked the price and found it was $38 I dug through my records to see what I paid for it years ago. My search came up empty handed.
so much for my complete collection of expenditures. Hah ! But I do remember bitching about the RockAuto.com shipping charge being over 25% what the item costs.

Hint: the cap will last much longer if you take the following steps:
1) drizzle a few drops of coolant on both of the cap’s o-rings before installing
2) push down with your thumb (print) on the center of the cap when turning it. It’s impossible to cross thread that way, and very easy to cross thread if pushing down on the edge of the cap when turning.
3) another forum member posted this one: don’t crank down on the cap. It only needs to be snug. The o-rings are doing the sealing so the cap doesn't need to be tightened very much for them to work as designed. This tip alone will give your cap a much longer lifespan.

Z

 

I had the same problem and it turned out to be sludge in the overflow bottle in the right hand wing. It is easy to get to and remove. It was not obvious from looking at the clean coolant within it, before removing it, but once removed found sludge in the small tube entry orifice. Cleaned that out and much better now, not a top up bottle float problem at all.

 

What prompted you to check the overflow bottle? And why would sludge be the issue?

Zray, I ordered the SKP tank and it should be arriving by tomorrow. If you recall, did you use the sensor that the tank came with without issue or did you swap for the original sensor?

 

I believe I used the sensor that came with the new aftermarket piece. It only senses the presence or absence of the “donut” free floating part that fits inside the tank on the vertical rod. It’s just an on or off sensor, so no danger of something not being calibrated correctly.

someone please chime in if I have described it poorly.

Z

 

I believe that fluid moves to and from the overflow bottle as the temperature of the engine changes. The sludge was preventing mine from allowing this to happen fast enough, so when sat in traffic and the engine got hot, I would get a low coolant warning, but when going again, the warning would go away. I put my ODB scanner on and monitored engine temp for a whole drive and found it was fine and not over heating at all, but when it got hot for a little while, the low coolant would come on.

 

FWIW:
I just checked the Rock website, and they now only list the URO brand for $56 and change. I bought two of these from A- Premium on Amazon, one in 2018 for my '99, and one in May 2024 for my '98. They both have performed well. Currently priced at $35.86 including cap and sensor.

Best, Rick

 

The SKP tank from rockauto arrived today. However, before installing, I'm going to check the recovery tank for sludge. The pictures you posted are quite convincing and the symptoms match mine.

I'll clean it and then drive the car until it's hot enough to see if the low coolant warning returns or not. If it works, I'll just keep this tank for when the current one fails.

 

I have a URO one in my XKR currently (least favorite brand but all that was available at the time) and its been working fine for a year now.

 

I just got done with inspecting and cleaning my recovery tank. It did have sediments, and sludge, but much less than what your pictures showed. The hoses to it were clean.

 

Cleaning the atmospheric recovery tank did not resolve the issue.

I have proceeded with changing the expansion tank and sensor. I noticed a little bit of green corrosion on the harness contacts. I am making liberal use of contact cleaner and light scraping of the contacts until they look clean.

I hope this finally solves my issue.

 

Do note that if you remove the sensor, which is easy and just clips out, that it has an orientation in the clip, it is easy to clip it back in without getting it quite rotated in the right place and then it will sit just a little bit lower in the tank. Don’t know why, but for some reason there is a cross piece in the round clip on the bottom of the tank that the slight gap on the sensors clipping edge needs to sit in to get it to sit flat and at the right height.

 

Final update:

The new SKP tank and sensor seems to be working fine. The low coolant warning has not returned, but more testing is needed.

I know this is not the topic of the thread but…
To my horror, when I was replacing the atmospheric recovery tank after cleaning it yesterday, I noticed the outer brake pad of my front right brembo caliper was wearing unevenly. The outer pad was worn more than the inner one, but one of the edges of the pad had more wear than the other one. I bought new pads and began the brake job, only to find that the dust shield of one of the pistons had broken, which I guess explains the uneven wear.

Does anyone know where I can buy a caliper rebuild kit for the front brembo brakes?

 

Some time ago I bought from Bigg Red UK. Good quality rebuild kits.

 

Thank you! I was able to purchase a kit that includes the pistons before I saw your reply. I'll keep them in mind for next time.