Tonight the plastic coolant overflow tank decided to burst into three pieces. I am wondering what might have been plugged or restricted that might have caused the tank to over pressurize. Or it might have been the fact is plastic and degraded.

Any thoughts? I am going to replace it tomorrow, if I can find one local.

 

I have had one fail and have a leak now. I have a concern about not only the plastic overflow tank but all the other plastic parts on and in the engine. Everyone believes that the XK8/R is a classic that will endure forever but what shape do you think the plastic will be in when the cars are 50 years old like the E types?

Excess pressure is released by the cap on the reservoir. Heard of it failing by not holding pressure but not from too much pressure.

 

I have already replaced all the plastic on the front of the motor. It all came out in small mushy pieces. My tank actually exploded into three pieces going through the drive through at in-n-out, what a scene. The service life of my plastic cooling system seems to be about 7 years, so in 50 years you will have replaced them at least 7 times. I know you can get some of the parts from a vendor on this forum that are aluminum.

If your cap is leaking on the top of the thermostat housing, check the threads on the housing. My housing was cracked and I could not get that cap to seal. I thought it was the cap and went through about three until I spotted the crack in the housing. When I was taking it apart it started crumbling. So I replaced everything plastic... except the tank. What a mess.

 

What a shame using cheap stuffs like plastic in a Jag . I had seen a Mark V when it was 49 years old and they told me that that ride was still using original factory radiator and tank , I was so flabbegusted when I heard of that .

 

IDK, Its not that they used plastic. Plastic is a viable material in most applications including aircraft and space travel. It's the type of plastic and where they used it. My Ford truck has a clear plastic coolant overflow tank and its fine. In fact it will never need replacing unless it is physically damaged.

I am wondering how many jag radiators are filled with the mushy plastic debris from those parts.

 

someone should develop an all-steel cooling system set. Stainless steel overflow tank and braided stainless steel for all other fittings. It would be expensive but not as expensive as replacing the stupid plastic ones all of the time.

 

THe issue is that this is not an 'overflow' tank, as it is at full cooling system pressure.

The typical overflow or 'coolant recovery system' uses an overflow tank that is not pressurized. The radiator cap has a pressure relief valve that, when overpressured, allows coolant to flow to the tank. The cap also has a vacuum valve that allows coolant to be pulled back through the cap when the system cools down and the coolant shrinks.

The Jag (and some other modern cars) uses a tank that is at full system pressure, and as such, can burst when the plastic weakens through age. I'm not sure what the advantage of this would be except, perhaps, reducing coolant oxidation due to contact with air in an unpressurized overflow tank.

 

I agree that the tank is at system pressure. But the problem seems to be the degrading plastic material. Those "other" plastic overflow tanks retain their integrity. The plastic cooling system parts in the jag don't retain their integrity and actually crumble.

 

Yes, I agree that the plastic they used may have not the be best longterm choice... I've found the same in 80-90's Japanese cars. They appear to have learned the lesson earlier and changed to something with a longer life.

The issue certainly shows up as more catastrophic when the integrity of the sealed cooling system is lost due to plastic failure.

 

A radiator tank that is under pressure is not a recovery or overflow tank, it is an integral part of the radiator system. Most modern cars with crossflow radiators have such a tank mounted remotely from the radiator and they are usually plastic and have a pressure cap. The Jag overflow or recovery tank is under the left-front bumper and is invisible unless you get under the car. As you pointed out, it's job is to recover coolant which is released by the pressure cap when the engine gets hot. This tank is not pressurized. You ask why is the pressurized tank plastic....simple, it's cheaper to manufacture.

 

Apparently, plastic cooling parts fail on some cars and not on others. On the other, less technical forum, someone made the conjecture and offered links to an anti-freeze site that discussed anti corrosion additives in anti-freeze. The site claimed that different plastic compounds were attacked by some of the "standard" anti-freeze compounds. I am wondering if anyone who has used Jaguar brand anti-freeze exclusively has experienced the plastic failure?

 

Excellent point about the antifreeze formula. I've preached endlessly about the importantance of using the correct, factory specced coolant formula for the given MY. In late model Jaguars (1999, mid-year on), an OAT formula is specified. Jaguar designs all of the cooling components, including plastic compounds to be compatible with the specified formula. So, when owners choose different formula types, e.g - HOAT, NOAT, traditional green, phosphate, non-phosphate, etc., they are playing with chemistry that might have longterm ill-effects with little understanding of the real cause for failures or the nexus to the coolant formula.

The other issue - cracked bleeder cap on the thermostat tower is ALWAYS caused by overtightening this cap. Here is a tip for sealing this plastic cap with a guarantee it will not leak....or crack. Wrap the threads three or four times with plumbing teflon tape, wrapped in a CLOCKWISE direction when looking down at the tower. Replace the cap and HAND- TIGHTEN, If there is any seepage of coolant after the engine has warmed up and cooled back down tighten about 1/16th of a turn more with an allen wrench. This tower cap will NEVER leak and should never crack thereafter. It has to be a new cap however, if the old one is already stress cracked from overtightening.