Recently bought a John Deere 650G dozer, SN 743651. It started burping coolant out the radiator overflow nipple. There’s no overflow tank, so it just sprays forward. I installed a new 7 PSI cap (per the manual). That didn’t stop it. I put a manual temp gauge on it. It never goes above 145–165°F. Today with a radiator pressure tester on it, temp never went over 140°F. I’ve run 3–4 combustion gas leak tests. All negative. Fluid stayed blue even while I could see it bubbling in the tube. Left it on 3–4 minutes with no color change. Stuck the same tester in the exhaust and it changed immediately, so the kit works. Ran it at 50–75% throttle with the pressure tester on. System built to about 14 PSI, briefly hit 16 PSI when I idled it down, then settled back around 14 PSI. Still never over 140°F. Oil and filter were just changed. Oil is clean — no sign of coolant in it. Machine runs well and starts on the first turnover. I can’t figure out what’s causing the bubbling in the radiator. Next step is to pull the water pump belt and see if the air bubbles stop. Any recommendations on what to check next?
Head gasket.
Thanks, I just thought a head gasket would be showing more signs like water in oil, failed combustion gas test. etc.
Took the water pump belt off and it wasn’t bubbling. However, I didn’t run it very long. What could cause the bubbling with the water pump?
No water pump flow means any bubbles formed from a failed head gasket are probably trapped in the head, for now. The circulation from the water pump moves the combustion gases to the radiator.
Shouldn't it fail the combustion gas test if it's combustion gases?
I have no faith in those combustion gas testers.
Interesting….as I tested our Hitachi EX270 with a combustion gas tester...it showed no color change. Yet the radiator was creating significant pressure and ‘blowing steam’ At the time I wondered if the tester was actually indicating true values/pressures in radiator.
Before you start pulling the head, can pressurize each cylinder to verify there's a leak?
I opened the thermostat housing and it didn’t have any in it. I put two new ones in and it’s getting to about 185 now. I pushed with it about 20 minutes and it didn’t push any coolant out of the radiator. Temps stayed below 190. Had a pressure cap on it and it got between 6-7 PSI. When I turned it off it hold pressure for a good 10-15 minutes. I’m going to run it more tomorrow to see how it goes. The waterpump was rebuilt not long ago. Maybe a new pump was constantly turning water to the top of the radiator and creating foaming.
Run it for couple hours today. It's still pushing out the overflow nipple after an hour or so of running. It doesn't have an overflow tank, so it just sprays out. The oil still looks great. It's staying around 175-190 Temp. Yesterday, it held pressure on the system after I shut it off for a good 10-15. I figured it would leak down if something was leaking.
Are you saying it's missing an overflow tank that's supposed to be there or never had one at all? Since you have the overflow nipple, any chance you can rig up a diagnostic overflow bottle from a 1 gallon milk jug? I think the typical one gallon translucent (not clear) plastic jugs are HDPE which should easily withstand hot fluid for a bit. Run the hose to the bottom of the jug so it can suck back any overflow once the engine cools. Watching the level of the coolant in the jug when cycling the engine from cold to hot and back to cold should tell you if you have air being introduced.
Yes, according to the manual SN 743651 doesn't have an overflow tank but it has the nipple there for a tube. Yes, I thought about buying a aftermarket overflow tank, but a jug sounds easier. I will get a hose and try that.
How far do you fill it up? If there's no expansion tank you don't fill close to the top. The antifreeze will expand and blow out. With cold anti freeze it should be down 1.5 to 2 inches.
I've been stopping a couple of inches from the top. I talked to one guy that had a 700 John Deere, he said you could only put 2 gallons of coolant in it because it would blow it out if you put any more in it. He said it never got about 190 degrees. I still think something its aerator the radiator. It's not foaming as bad now but still bubbles a little.