G5200 Cooling System

[Baby Grand]

I've noticed the temperature gage has been steadily finding a higher max operating temperature over the past 2 years. Last week it overheated while The Plant Manager was cutting the not-too-long lawn on a not-too-hot day, so I decided to see what was causing the problem. After some testing with an IR temperature gage, I determined that the thermostat wasn't opening until the temp gage was touching the red mark, so I ordered a new thermostat & gasket.

The old thermostat gasket was a paper composition type and had been RTV'd to seal it up. The new one is some kind of springy metal coated with a dark surface finish. Got it all put back together & it leaked like a sieve. Luckily, I had saved the old gasket, which was in almost new condition. Got everything back together, with some fresh RTV, ran it & it still ran too hot for my liking, even though the thermostat was now opening up at a lower temp. There's a coolant drain valve on the driver's left side of the engine, but when I opened it, nothing came out. I took the threaded plug out & tried to run a piece of wire up into the valve body, to snake out any obstructions, but the valve passage dead-ended. So I go out the twist drills and carefully started clearing the valve passage, starting with a 1/16" bit, in a hand chuck, and working up to 1/8". I kept getting grey, clay-like sludge in the drill flutes, but no coolant flowed out. So I decided to remove the port from the block with a wrench applied to the hex on the valve body. I was shocked that with just a little torque, the valve body sheared off, leaving the threaded hole in the block filled with the valve's threaded part:



Ugh! Ordered the replacement valve (which I learned is call a "drain cock") from Messick's, which arrived within about 48 hours of placing the order - really amazing. In the meantime, I decided to take the radiator out, clean it & straighten out the fins that had been folded over by a close encounter with a spinning fan and various other dings that have happened before I bought it, a few years ago. Getting the radiator separated from the tractor proved to be a major job. Maybe there's an easier way, but I ended up taking the fiberglass deck off to get access to all the fasteners:



This gave me an opportunity to clear all the caked on dust & grass clippings from every nook & cranny with an air gun. With the radiator off, fin straightening could proceed. This was slow & steady (and tedious) work, but went without a hitch.

Before:




After:



Removing the piece of the valve body stuck in the block did not go so well. An easy-out just smeared the pot metal, or what ever that thing is made of. I ended up hand turning progressively larger bits until I started contacting the threads of the block. Then I had to use a hardened pick with a right angle bend to scrape the pot metal out of the threads, which took about 2 hours. That being done, the new valve was replaced and everything reassembled.

I loaded the cooling system with straight water, ran it for a few minutes and drained it, getting lots of gunk & cloudy water in the collection bucket. Refilled the cooling system with straight, filtered water and Zerex cleaner and cut some thick grass for about half an hour. The temp gage stabilized a full 1/4" below the start of the red - success! I'll run it with the Zerex for a few hours, then drain & refill it with usual 50/50 water/coolant mix and keep an eye on the temp gage, but I think the problem is fixed.

-Jim

 

[artfull dodger]

I would say that cooling system was probably never serviced by the book. Good job on solving the overheating issue. Mike

 

[bones66]

I had a G5200 and loved that thing. I had the same problem, it tended to run a little on the hot side according to the gauge. I did some research and couldn't find any permanent solutions. I kept a constant watch on it and made sure to blow all the debris out after each use and it never overheated, but probably did run hotter than intended. The HST was really strong on that mower. The deck had some welding done on it and was beginning to need a little repair again. When I got my 5200 the steering had tons of play in it but Kubota offered a kit to fix that issue. The kit replaced most parts in the steering an wasn't easy but did take care of the problem. Good reading about your fix.......makes me wonder if I had done that (except the broken drain cock issue)maybe I would still be running around cutting grass on that thing.

 

[Baby Grand]

Mike - The Plant Manager cut for a few hours on Monday (in the 90's, here, and very humid) and says the gage never went over a 1/4" below the red, so I'm guardedly hopeful. I'll drain the Zerex mix, this weekend, give it a good flush and recharge with coolant mix.

bones - I love this G, too. Can't tell you why, precisely. It's an old, cantankerous machine, but I just love mowing with it. I find myself in (playful) conflict with The Plant Manager for seat time on it, because she really likes to run it, too. I can't begrudge her a little tractor seat time of her own, so I usually take care of trimming the edges with a line trimmer.

Thanks for posting about the steering fix - any chance you have a part number(s) for reference? Ours has a little more play than I'm good with and I know it isn't going to get any better on it's own. First I've heard of the kit. Did you buy your G5200 new? BTW - this is why I love TBN, the collective experience of so many good people is a kind of information gold mine for anyone who'd "rather do it themselves".

Jim

 

[bones66]

.....................................

bones - I love this G, too. Can't tell you why, precisely. It's an old, cantankerous machine, but I just love mowing with it. I find myself in (playful) conflict with The Plant Manager for seat time on it, because she really likes to run it, too. I can't begrudge her a little tractor seat time of her own, so I usually take care of trimming the edges with a line trimmer.

Thanks for posting about the steering fix - any chance you have a part number(s) for reference? Ours has a little more play than I'm good with and I know it isn't going to get any better on it's own. First I've heard of the kit. Did you buy your G5200 new? BTW - this is why I love TBN, the collective experience of so many good people is a kind of information gold mine for anyone who'd "rather do it themselves".

Jim

Sorry but I don't remember that number for the steering fix. I really think it's kit as every thing came in one box and complete instructions for the installation. I might be wrong it's been a few years now, My tractor was in extremely nice shape but the deck was weak. I bought it used from a friend and he did the rework on the deck and did a nice job on the areas he addressed. I just wish he had addressed a couple more areas. The engine on my tractor was clean as a whistle. Lots of fun to mow with an twice a nice when I got the steering fixed!!!

 

[artfull dodger]

I would not totaly trust the accuracy of the factory gauge either. My oil gauge in my old Dodge pickup never reads very high, but on a good mechanical gauge, she has loads of oil pressure. If you have access to a infared temp gauge or a different temp gauge that actualy shows the temp and not just lines, then I would verify the accuracy of the factory gauge. Mike

 

[Baby Grand]

Good point about the gage accuracy. I did use my trusty HR IR meter to check the thermostat operation, and I'll try to correlate what it says vs. what the temp gage says.
-Jim

 

[Baby Grand]

Following up on the gage calibration/accuracy topic that Mike brought up:
Here's the gage after 1/2 hour cutting field grasses (12 - 18", dry) in mid 80's temperature. Engine has been off for 3 or 4 minutes, so a little soak-back temperature rise:



This is a bit higher than where the gage was reading during the heaviest cutting - it was consistently centered between the hash marks. Just before I shut it down, and right after I popped the hood I took some spot temps - engine was running at medium speed, unloaded. This one is the highest temp that I could find on the radiator:



Here's the exhaust manifold high temp:



... and the highest temp I could find on the block/head:



I'm happy with the results - a big drop in operating temperature & no boiling over.
Drained the Zerex cleaner/water charge & refilled with Prestone 50/50 mix.
-Jim

 

[artfull dodger]

Looks good to me, great result to the problem. I have been trying to get our shop to purchase one of those IR heat temp readers. Would come in handy to see if one of the cylinders in an air cooled twin was running lean/hot. A common issue with the newer twin bore carbs. Mike

 

[Baby Grand]

Mine is a Horrible Fright cheapie and has easily paid for itself ($35) in the first 3 months I had it. Bought it for figuring out what was going on with an old wood stove that had draught/cool running problems - really helped me nail down the problem. Helped me diagnose and repair a failing-but-not-noticeably-bad thermostat on my car that caused me to fail an emissions test. Plus, it's very useful in the kitchen!