John deere coolent issues.

[Tay14]

The father in laws 2003 6820 has developed a coolent fault.after about 10mims of running the pressure In the coolent system increases and eventually blows its pressure through the header tank cap and down the overflow pipe. if you run the tractor with the cap off it will blow small amounts of water out randomly.
the things I have tried so far but the issues are still there.

removed both thermostats
pressure test coolent system all ok
no water in oil
engine runs fine
carry out sniff test/ Co2 test.no exhaust gas in coolent
flushed coolent system and clean out radiator

one thing I have noticed is that there seams to but good water pressure near the water pump,good water pressure from the thermostat bleed screw but if I remove the top hose which runs to the top of the radiator there is very low pressure as if the water pump carnt pump coolent all the way round the engine?possible bad water pump? thanks paul.

 

[Lofty1984]

@Phil P

 

[Phil P]

Release pressure from rad, replace cap, start engine (tick over). Now squeeze the top hose and if you can feel it build pressure (like it’s been pumped with a bicycle pump) within 30 seconds - a minute your head gasket has failed.
If the engine isn’t running hot under load your water pump will be fine, they get hot QUICK when the pump fails.

 

[jd6820]

Release pressure from rad, replace cap, start engine (tick over). Now squeeze the top hose and if you can feel it build pressure (like it’s been pumped with a bicycle pump) within 30 seconds - a minute your head gasket has failed.
If the engine isn’t running hot under load your water pump will be fine, they get hot QUICK when the pump fails.

Yeah this is what I’d be thinking. Sniff test isn’t always accurate. As you’ve established there should be no water bubbling out of the tank with the cap off even with the engine running. As Phil says when the water pumps go they get hot real quick, you’d know if that was at fault for sure. I’m tempted to say head gasket with the symptoms shown. By the way, they don’t often mix fluids on these when the gasket goes. In fact I don’t think I’ve ever seen them mix with engine oil yet gasket had gone so bad it was hydraulic locking, then when running you couldn’t fill the header tank as it was blasting out and covering me and the underside of the bonnet. Yet no other signs of mixing oil or leaking between head and block etc...

 

[cousinjack]

Head gasket would be my port of call...