# Air in cooling system



## JMT (Aug 10, 2013)

My John Deere 6430 is losing coolant through pressure relief/overflow in the plastic "radiator" cap. At first I thought that the cap was not holding enough pressure as the cooling system heated up, but now I think that air is accumlating in the system.

Air is venting through the overflow about every 30 seconds. I can plug the overflow with my finger and air will accumulate until I release it. Without plugging the overflow, it will just do a small "burp" to vent pressure/air. When coolant is at normal level some is getting carried out with the air release. Cooling system seems to work until coolant level drops.

What can be the cause of the air in the system? Any replies are appreciated.


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## Vol (Jul 5, 2009)

http://manuals.deere.com/omview/OMAR283034_19/RW29387_00005A0_19_12DEC08_1.htm

Inspect the cap for defects.

Regards, Mike


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## glasswrongsize (Sep 15, 2015)

Knee jerk thought is head gasket. 
Someone else may know something more model-specific

73, Mark


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## JMT (Aug 10, 2013)

Vol said:


> http://manuals.deere.com/omview/OMAR283034_19/RW29387_00005A0_19_12DEC08_1.htm
> 
> Inspect the cap for defects.
> 
> Regards, Mike


I replaced the cap and the new one is doing the same thing.

When I plug it with my finger it does not take much pressure to plug it. Maybe the new cap is faulty too. Neither one have any visible defects.


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## mlappin (Jun 25, 2009)

glasswrongsize said:


> Knee jerk thought is head gasket.
> Someone else may know something more model-specific
> 
> 73, Mark


Unfortunately that's been my experience as well.


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## VA Haymaker (Jul 1, 2014)

glasswrongsize said:


> Knee jerk thought is head gasket.
> Someone else may know something more model-specific
> 
> 73, Mark


My thought too...


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## Farmerbrown2 (Sep 25, 2018)

Dad had a Farmall MD with a cracked sleeve I remember him showing me the tiny bubbles in the radiator. Wish you luck.


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## Wethay (Jul 17, 2015)

Head gasket or a pin hole in a sleeve are my go to ideas, but I hope I'm missing something simple and inexpensive. A radiator pressure tester would take the place of a cap and allow you to see how much pressure builds. If you were to get the system up to operating temp, then put the radiator cap on there should be no more expansion in the system to worry about so even a weak cap should keep everything in place. There are test kits available for detecting exhaust gasses in coolant, I believe an auto parts store would carry them.


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## JMT (Aug 10, 2013)

Thanks for the replies. Would be nice if it was something inexpensive and simple, but I think you all are on the right track.

Any rough ideas on a repair cost?


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## Farmineer95 (Aug 11, 2014)

Can try leaving pressure tester on overnight. Next morning see what the gauge does. Loosen oil drian plug and see if it is antifreeze first. Does it have egr cooler? Might see residue in exhaust if leaking antifreeze. Does air from vent smell like exhaust? Might be hard to detect.


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## JMT (Aug 10, 2013)

Thanks for your reply. I let Deere dealership have it. Called my service tech to come look at it, but after hearing what it was doing he said it needs to go to the shop, that it does not sound like a simple fix.

Thanks again for the responses.


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## JMT (Aug 10, 2013)

Tech thought head gasket was strong possibility.


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