XJ6 & XJ12 Series I, II & III 1968-1992

coolant overflowing

 
  #1  
Old 09-20-2014, 10:42 AM
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Default coolant overflowing

Hello everybody,*
I recently bought a xj6 from the original owners carport since 2006, it only has 56000 miles and have just got it back on the road. I replaced the tyres, all the coolant hoses, the radiator and thermal switch for electric fan. I drive the car 45 miles each way to work every day and it runs beautifully at 85 degrees however, after I arrive (anywhere) and turn it off, the coolant expands and fills the overflow tank in the left front fender and continues to overflow about 2 quarts on the ground. I catch it in an old antifreeze bottle, refill the expansion tank before restarting and off I go only to have it repeat next time I shut it off. I also replaced expansion tank cap with a new one. Anyone have any thoughts as to why coolant expansion is so much?
Thanks
Daniel
 
  #2  
Old 09-20-2014, 11:22 AM
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Might be an airlock or blockage.
Try replacing the thermostat and flushing system out.
Refill and bleed properly. Heater set to hot
I also find it helps to undo one of the pipes at the highest point when refilling.

Does the coolant smell of exhaust? Could be worth doing a sniffer test to rule out head gasket.
 
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Old 09-20-2014, 11:36 AM
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I flushed the coolant when I repaced all the hoses. No abnormal smell to it, I have not replaced the thermostat but will try that. Do you think it could have an airlock even though it has about 1000 miles on it since I did hoses and radiator all freeway miles between 70-80mph? Never runs over 90 degrees and usually hovers around 85. I took the heater valve out as it was corroded and (for now) just run a straight piece of tube in its place (always flowing through heater core)
Thanks
Daniel
 
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Old 09-20-2014, 11:38 AM
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I have pressurized the system to 16Ibs cold with no leaks-holds pressure
 
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Old 09-20-2014, 11:49 AM
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I have seen this happen on two occasions, but the reasons were totally different.
The first time I saw this was due to a large air bubble/blockage...the coolant amount in the XJ6 is larger than a lot of vehicles and I've had trouble "burping" mine. Parking on a hill and loosening or removing a top coolant line can sometimes help. The second tiime I saw this happen was due to bad coolant. The car was fine when it was running and cycling the coolant, but when it was shut off, the coolant boiled in a few hot spots, pushing a lot of coolant out of the overflow. I'm sure there are several other possibilities, but it sounds like something is causing pressure to build after the coolant quits cycling. Loose pressure caps can also sometimes contribute to this problem as they keep the normal amount of desired pressure from building up and lowers the boiling point of the coolant. Good Luck!!

Jim
 
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Old 09-20-2014, 11:59 AM
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Well, I will try draining out the existing coolant and refilling with new whilst bleeding it with top hose cracked open. Is there a prefered antifreeze for these engines? 4.2 injected
 
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Old 09-20-2014, 05:13 PM
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Do you have the correct pressure cap on the expansion tank ?
When a car is shut off after a reasonably long drive is when the coolant temperature rises to its maximum, as there is no longer any cool coolant coming in from the radiator, but the engine is still very hot. So the pressure in the system rises and the pressure cap should prevent boiling by keeping the pressure in the system. In you case, I would suspect the pressure cap is no good or the wrong one. So with little or no pressure in the system the coolant is boiling and going into the expansion tank and out the overflow pipe.
 
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Old 09-20-2014, 05:37 PM
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Fraser,
Thats the mystery! I have a brand new 15Ibs cap from welsh ent. And it does build up pressure underway as it should, but ONLY after 3 minutes of shutdown does it start overflowing. It sucks it all back in as it cools except what I catch leaking out of overflow.
 
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Old 09-20-2014, 09:02 PM
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How much coolant are you putting in the brown header tank? Are you filling it more than about half way?

If so, stop.

Next time it pukes out coolant do nothing except let it sit until cool. Then open up the brown header tank and check the level. If it needs topping off don't go higher than about half way. A bit less tha half way is fine.

Repeat this for a few drive cycles and see what happens.

My guess (Not so much of a guess, really, as I've seen this a dozen times) in that the system (including the atmospheric catch bottle inside the fender) is simply overfill. Let the system seek it's own level and tell us if the coolant puking stops :-)

Cheers
DD
 
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Old 09-21-2014, 08:26 PM
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Hi Doug, thanks for that post. It clears up something. I've always been puzzled that my overflow settles under half full. Temp gauge is good, no leaks, no mixing with other fluids, tranny fluid clear, etc. I always thought maybe it should be filled more but good to hear you say keep it on the lower side.
 
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Old 09-22-2014, 06:16 PM
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Doug,
I also wondered about this but found if I don't fill coolant back up with what came out my low coolant light comes on. I have tried starting it cold, and filling it just until the light goes off (a little under 1/4 full in expansion tank) and driving around locally have no issues, however after my 45 mile freeway at around 65-75mph it still dumps out about a quart from the overflow tank. I have not yet changed antifreeze again and thermostat.
I tried leaving it one day (knowing that when hot it would expand) but the light stayed on for almost my whole drive. I kept a keen eye on temp gauge and its happy between 85-90 underway. I can turn it off, wait 5 minutes for it to start overflowing then turn key on (without starting) to see what it reads, and its around 95

Daniel
 
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Old 09-22-2014, 07:22 PM
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Shoot! I was hoping for the easy fix.


I'd be tempted to change the thermo on general principles but it really deosn't seem like a thrermo problem. And you already have a new cap.


Now I'll have to do some thinking.


Cheers
DD
 
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Old 09-22-2014, 08:52 PM
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I still have the old cap, I think I'll try it tomorrow (just because I can!) And unfortunately I have no idea what it did before changing hoses and radiator as I had towed it on a trailer home (original tyres where still fitted with cracks I could put my fingers through!).
I did not drain block but by replacing radiator and having all hoses off at one time thought it was drained enough. I will flush it properly soon though.
Daniel
 
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Old 09-23-2014, 06:53 AM
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I have to say I suspect the head gasket, they don't normally manage to get past about 85k miles even with the slotted block that stops the inter-bore cracking.
 
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Old 09-23-2014, 06:59 AM
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my head gasket made it to 89k does that make it special??
 
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Old 09-23-2014, 02:32 PM
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Originally Posted by Darrenmb View Post
my head gasket made it to 89k does that make it special??
Very !
 
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Old 10-02-2014, 10:02 PM
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Ok, so I finally dug out the original 15 Ibs cap that is sort of rusty and swapped it with the new cap. Problem solved. I am more frustrated with myself for trusting a new cap. It really goes back to 'kiss' keep it simple stupid! Thanks to all for recommendations and help, i can't believe i drove for 3 weeks catching and filling my coolant! Now, onto the dripping right side fuel tank when I put in more then 3 gallons!-new tank needed i believe.
Daniel
 
 
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