The MY97 coolant reservoir exploded and was replaced last night.(please refer to my post yesterday. https://www.jaguarforums.com/forum/x...beware-137040/)

While test driving it this morning, it reached normal temperature and held there for about 10 minutes before the needle started to climb steadily and the red overheat light came on in less than 5 minutes. I pulled over and noticed that I left a trail of coolant on the road surface. The trail is in line with the driver's seat, i.e. right side of car as mine is a RHD. I checked page 23 of the SNG Barratt XK8 parts catalogue which showed that there is an Atmospheric recovery bottle which catches the overflow from the Coolant Reservoir. But I could not locate the Atmospheric recovery bottle on my vehicle. Would a fellow XK8 owner be kind enough to show me where it is located?

I am really baffled as to what is causing this overheating and would like to hear from you experts. TIA.

 

The recovery bottle is behind the plastic wheel well.

The system probably has air in it. With the reservoir full and the cap off 'burp' the radiator hoses as the engine warms up. It would help to fill the system from the thermostat tower but be very careful removing the cap. It is now 18 year old plastic and using a 10mm Allen Wrench is guaranteed to break it. Use a strap wrench.

 

I would follow Test Point's advice re: refilling.

I don't think you need to gain access to the overflow tank at this point. It is designed to dump coolant when its capacity is exceeded, and if your engine got hot enough you could have boiled coolant within the engine, which would have sent a large quantity to the overflow tank. Easily too much for it to hold. (Coolant mix boils at about 260 degrees with our 15 pound cap.)

In other words, nothing in your description of events indicates (to me, anyway) a problem with the overflow tank.

 

I took off the reservoir cap, noted the reservoir is half full, started the engine to warm things up while squeezing the upper and lower radiator hoses which are quite soft and squeezable. After reaching normal temperature, the water level in the reservoir begins to slowly rise. I switched off the engine and waited for the water level to recede, then filled up to the bottom of the neck and tightened the cap. Restarted the engine and soon the fans turned on and temperature showing normal and steady. The hoses are now quite stiff and become hard to squeeze under pressure from the water pump.

Its time for another test drive. First 10 minutes went okay and then the water temperature starts to creep up slowly from normal, and eventually the red warning light came on. Switching on the air conditioning to get extra cooling air through the radiator did nothing. I was 30 seconds away from a safe place to pull over, but in 20 seconds another bang and a big puff of steam came out of the engine compartment.

Upon inspection, the bottom radiator hose came off of the thermostat front cover, spilling more than 5 litres of coolant.




Note: I moved the hose clamp to the left of the hose end to prepare for reinsertion.

Now the big question is: What is causing the overheating?

I believe it is a faulty thermostat stuck closed or partially stuck closed, not allowing sufficient coolant through the radiator, thus overheating the engine and building up a tremendous amount of pressure within the cooling system, and whichever is the weakest joint/point that cannot bear the pressure will give: it first split the top/bottom half joint of my 17 year old coolant reservoir 2 days ago, and today pushed the bottom radiator hose off the thermostat cover. Any comments on my diagnotics would be most welcome.

Please give me pointers as to what to watch out for while replacing the thermostat, as well as any improvement(s) to carry out while I'm at it. TIA.

 

Please do not reuse that lower hose!

The thermostat is an excellent choice for the source of the problem but you obviously have others. The bulged short hose between the cross over pipe and the thermostat housing will the next to go and the lower hose shortly after.

Time for the full Monty including the thermostat, water pump, cross over pipe, all hoses and the aluminum thermostat housing.

Your car is 18 years old and it would appear from the picture the hoses are original. The next time the engine is overheated could be your last!

 

Thank you so much for your response. I have now ordered all related parts from the U.K. for a fully Monty as you suggested.

Cheers!

 

I was going to say also look at those hoses, they look horrible. As stated, replace it all.
Don't get your hoses from Jag, WAY to pricey, I got mine off Ebay. Replace the complete Tstat housing and stat, wp, all of it.

 

Looks like you have had SLOW leaks on the parts to the far right of your pic also. One can see the dried up coolant.

 

Compare your Bypass Hose in post #3 with this new one!



Graham

 

Test Point posted a good reply. When we service these cooling systems, most would simply fill the system through the reservoir. This traps air in the system. The engine temp will act exactly as you experienced. It is absolutely imperative that you fill the system through the plastic tower at the top front of the engine. As stated, the cap will probably crack if you use a 10mm allen wrench to loosen it, if it is aged. Either use a strap wrench, or simply get a new cap. Fill the engine here, until it will accept no more coolant. Secure the plastic cap, and top up the reservoir to the proper level. Run the engine. For me, a sure fire method to double check for trapped air in the system is to run the heater. If the heater gets warm, you are good. If you dont get warm air, run the engine speed up a few times and recheck. If you still get no heat, stop and start over.

 

Could it be that the coolant reservoir exploded as a result of overheating??

 

I'm quite certain the coolant reservoir was the weakest point in the entire cooling circuit and could not take the raised pressure due to overheating. After replacing that, next come the bottom hose connection at the thermostat cover.

 

The mystery continues...

Since taking out the thermostat is just 3 easy-to-get-to bolts, I figure I can just take it out and run the car until the new one arrives. But I cannot find anything wrong with the thermostat after taking it out. So I am now pointing my finger at the Water Pump. Can someone tell me if my diagnosis is correct or not? There are no strange noises coming from the water pump. Are there any other means to detect a failing water pump?

In the mean time, I guess I'll have to wait for the arrival of the Full Monty of cooling system parts I've ordered before dismantling the water pump.

 

The early water pumps were prone for the pedals breaking into pieces, (plastic), unless someone replaced it with the original type, it lasted much longer than most. Get one with the metal pump blades and be done with it. When you take it off and there are some missing parts, give it as much of a flush as you can. Then maybe it won't overheat in that stop and go traffic in Hong Kong, it's will be doing better than most if it doesn't.


Wayne

 

Thermostat test: It should be closed at room temp of course. Put it in some water on the stove and watch it as the water approaches boiling. Should be opening then.

I'd recommend against running with no thermostat at all. Life is harder on some components until the engine gets up to temperature.

Good luck.

 

I agree with all of the above posts. In addition, a thermostats often stick intermittently.

 

In preparation for replacing the water pump, I've read Gus' page on it JagRepair.com - Jaguar Repair Information Resource and would like some clarifications.

1. First of all, the water pump pulley should come off before you can reach the water pump mounting bolts to remove the pump?
2. I note the belt tensioner has a 15mm nut in the center. In order to release the belt tension to remove the water pump pulley, can I just pull on this nut with a wrench with sufficient extension to gain leverage, without worrying about loosening/undoing the nut? Or is there a better way to relief the belt tension for water pump pulley removal?

Fedex tracking says my order should be delivered Monday afternoon Hong Kong time (GMT+8). I'm keeping my fingers crossed. Thanks for all the help.

 

Just changed my pump last week. In answer to your questions-

1. Just loosen the pulley bolts before removing the belt. Remove the pulley after removing the belt.

2. The belt tensioner nut has what I think they call left hand threads. In other words it loosens by turning clockwise and tightens counter clockwise. So facing the front of the engine you need to pull on your wrench counter clockwise. Or if you are working from the passenger side (left hand drive) fender pull the wrench toward you to take the tension off the belt.

Hope this helps

 

Just noticed you are in Hong Kong so I guess you will be working from the drivers side not the passengers side. Sorry I did not catch that before.

 

On the X308 a common cause of mysterious behaviour in the cooling system
is the attachment of the bleed hoses. They are often installed in the improper
position because the arrangement is non-intuitive.

The X100 may have the same arrangement. You should go back and verify
that the hoses are indeed installed in the correct arrangement.

Then proceed with the rest.

ps. it looks like the cap on the cooling tower is toast.