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Discussion Starter #1
Hi all:

Still working on this 1999 diesel gator I got from my father-in-law. I've been working on it solid for eight days. Latest issue is the radiator fan. After I got it running I headed up the road for a test drive. After about a half a mile I turned around and came back. In that whole time the radiator fan never came on. Temperature outside is 70-ish today. I would think that would be long enough for that fan to come on. I checked the service manual and it looks like I have to pull the cab, seats, plastic cover and the radiator fan assembly to get at that radiator core thermostat, pull it out and stick it in a pan of hot water to test it. Holy crap.

Someone has cut about a 3 inch hole in the plastic cover above the top radiator hose. Through that I was able to stick a stiff copper wire down into the return side of the radiator fan and ground it. The fan came on so I know it's good. I pulled the radiator cap and there is coolant there, for whatever that is worth. There is about 2 inches of coolant in the overflow tank, again, for whatever that is worth. The temperature warning light never came on. It lights up when you first turn the ignition switch on so I know the lamp is good.

So, the question for the forum is this: is it likely that I could drive that thing a mile in 70° temperatures and the fan would never come on? Does anyone have any idea how I might test that radiator core temperature switch without spending an entire day tearing the whole thing apart?

There are so many ugly scenarios here. I suppose my thermostat could be stuck and no water is getting to the radiator. Maybe the engine temperature warning circuit is also bad. So I would have to have a bad radiator core temperature switch, a bad engine temperature warning light circuit, and a bad thermostat and/or water pump in order to damage my engine.

If anyone has any thoughts I would sure appreciate it.

Best regards

Mike
 

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Next time you're out check the return hose to the radiator. After a mile I would think you'd feel some warmth if the thermostat was opening. I believe the fan is meant to come on at 190*, but it is possible that a mile isn't enough to either trigger the overheat or fan switch. These engines run quite cool. Get an infrared temp gauge and check the temp at the thermostat housing.
One other thing, these things are a bear to burp all the air out. There's a plug on the intake manifold that's there just for that purpose. My "guess" is you're OK.
 

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Next time you're out check the return hose to the radiator. After a mile I would think you'd feel some warmth if the thermostat was opening. I believe the fan is meant to come on at 190*, but it is possible that a mile isn't enough to either trigger the overheat or fan switch. These engines run quite cool. Get an infrared temp gauge and check the temp at the thermostat housing.
One other thing, these things are a bear to burp all the air out. There's a plug on the intake manifold that's there just for that purpose. My "guess" is you're OK.
Hi, Cheapsnake!

Thanks for taking the time to reply. I will grab my infrared thermometer and head out. One of my worries is that there is not enough coolant in it. I couldn't get coolant to go into the radiator cap, but, as you said, with the thermostat closed it can be hard to get these things to take water. I propped the fill hose up with a stick so the inlet would be higher than the engine and was able to dribble about 2 quarts of coolant into it. That can't be good. When I drove it a mile, I parked it and let it cool off, and it did not draw water out of the overflow tank. Of course the overflow hose could be bad....

Having said all that, I devised what I think is a fairly ingenious if somewhat dangerous test for that radiator core thermostat. This could be a good trick for someone else who is in this position of having to spend a whole day's work in order to test that thing. I got out my 1200 W hot air gun and just blew hot air through the radiator grill up into that corner where the thermostat is. I kept the gun about 6 inches back from the grill (wouldn't want to melt that plastic radiator tank!!) It took about 15 minutes and that fan came on. Of course, I have no idea at what temperature, but at least I know it works. So now I am down to finding some way to ensure that there is enough water in it.

I tried to find that bleeder plug you mentioned, but I couldn't. I can't find it in the service manual, but it can be hard to find things in a 700 page e-book. I'm going to grab my infrared thermometer and go for a drive. I'll let you know what I find out when I get back.

Thanks again for the help

Mike
 

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Hi, Cheapsnake!

Okay! We have an update. Apparently the fan wasn't coming on because there was no coolant in the system. The 2 quarts of coolant I managed to dribble in there gave me a lot of information. About a half a mile up the road the fan came on. I stopped, raised the bed to do some of the temperature checking you suggested with the infrared thermometer and antifreeze was dribbling out of the radiator cap at a pretty good clip. So now I guess I know why there was no coolant in it. Still makes me wonder about the engine temperature light, but maybe I never ran it enough to overheat the engine with no coolant in it. So I will be getting a new radiator cap and do some more testing. I will post here what I find.

Thanks again for the help

Mike
 

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I've found it advantages to drill a small hole in the thermostat (1/8") to allow air to escape when filling. Also have the fill point as high as possible, which typically means raising the front end up on jack stands or other. Use a special radiator funnel and with extra fluid in the funnel squeeze the hose rapidly to get the water moving (Burp it). Some water momentum works wonders in clearing the air from the system.

Example of funnel: RADIATOR FUNNEL

With respect to weep hole... Some thermostats come with such a feature. SUPERSTAT (Read the features: "Technologically advanced designs use bleed notches, check valves, and other methods to assist in releasing air from the cooling system"

You might have saved yourself some time and perhaps frustration by purchasing the Technical Manual and understanding at what temperature the fan is designed to cycle on and theory of operation. My 855D temperature switch should turn on at.199F +/-5F.

Glad adding fluid solved your problem.
 

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Hi, Cheapsnake:
I do have the service manual. As I said in my previous post, I tried to find that plug you mentioned in it. I knew what temperature the radiator core switch is supposed to come on at. The problem is how to measure that. The service manual says you have to remove it and put it in a pan of water, heat the water and see what temperature it comes on at. Again, you're talking an entire day of work in the case of my gator with the cab on it. The manual actually says you should test that switch every time you change your antifreeze. I sometimes wonder what the guys are thinking who write these service manuals. I think your idea about the infrared thermometer should at least be somewhat helpful in this regard. I live 25 miles from town, but I should be in there tomorrow, and I will pick up a new radiator cap. After I am able to keep the coolant in it, that infrared thermometer might teach me something. That said, the fan came on yesterday, so I think the sensor is probably working okay.

I have seen thermostats with a small weep hole in them. I might just take mine apart and see if it has one. That said, as I was driving yesterday with my infrared thermometer, and actual antifreeze in the system, I watched that top radiator hose with the thermometer as I was driving. It held pretty steady until all of a sudden it started warming up about a quarter of a mile down the road, so I think it is safe to save my engine thermostat is working.

Your link to the "radiator funnel" took me to a John Deere technical page, but I couldn't find any route to the funnel you mentioned.

I looked at the article about the Stant "superstat". It sounds like a lot of really good engineering is in that thing, but I couldn't find a listing for the John Deere gator on the website. Again, I think mine is working as intended. My father-in-law, bless his heart, was not the best at maintaining his stuff. I hate to think how long he drove this thing with no antifreeze in it. It is likely he never ran it long enough to get the engine overheated, as he only has 10 acres.

Today I'm going to work on figuring out how to cover up that hole someone cut in the plastic above the radiator, fix a bunch of cracks in the roof, get the brake/tail lights working, and address some rusted through spots in the bed.

Thanks a lot for your help. Especially the idea about the infrared thermometer. I'm a little embarrassed that I didn't think of that.

Best regards

Mike
 

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Good work Mike, I truly wouldn't fret about your thermostat and fan switch until you have a fully burped system and the easiest way to do that is to find the plug on the intake manual. It's right at the top of the manifold to the rear of the carb. It actually looks like a attachment bolt, but if you loosen it you'll either see coolant flow from it or air hissing. Leave it out and fill the radiator, as 200mph mentioned, with the front raised slightly. Once you see coolant at the plug you're good to go. Don't worry about the hole in the thermostat, the plug accomplishes the same thing.

Rest assured, you aren't the first to have problems with air in the coolant system. It's a common problem that the manual does a really crappy job of addressing. Thanks for keeping us posted.
 

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Hi, cheapsnake:

Thanks again for the help. I think I understand why I'm not finding this plug. Your post said " It's right at the top of the manifold to the rear of the carb.". Mine is a diesel, so I'm thinking maybe it doesn't have this plug. I sure couldn't find any mention of it in the service manual, and you're right they don't give you much help about getting air out of the system. I did jack up the front and I have been dribbling 50/50 in there a few ounces at a time while I work on other things.

Hopefully I'll get a new radiator cap tomorrow, if they have one in stock, and then I can road test this cooling system. I agree that I don't appear to have any trouble with my thermostat or radiator core temperature sensor. I made an aluminum cover to cover up the hole someone else put in there above the upper radiator hose. Now I wish I had not put that on there, as it would be much easier to monitor the operation of that fan while driving. I'll let you know what I find out.

Thanks again for the help. I'm a fairly good mechanic, but first time around on a totally different machine is always challenging. John Deere buried the cooling system pretty bad on these old gators. Not sure how the new ones are. Hopefully better.

Best

Mike
 

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DOH! Diesel would explain why you wouldn't find the the carb. I think you're well on your way to getting that bad boy on the road.
 

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Mike, if you do not have a bleed screw on the cooling system, here is a trick my dad taught me many years ago. Take your new (or old) thermostat and physically deflect the movement. Place a large aspirin in the gap. With the gator oriented with the radiator fill port at the highest point (for burp purposes), install the stat, reassemble and fill the coolant. At that point you should be relatively air free. Naturally do the stat installation last, as the aspirin will start to dissolve when moisture gets to it. Immediately start and run to circulate fluid before the aspirin dissolves and closes the passageway. Check later that the fluid is at the proper levels. No air. Click-pow.

I would strongly suggest that while you are doing this, go to the dealer and get a dealer stat, not a parts store unit, which may or may not be the right one. You are on the right path of a new dealer cap. Many people overlook the cap as an important component. It is critical, just like the pump and stat. Some cars (like Subaru) are dependent on dealer parts in the cooling system and will not function as intended if anything other than OEM is used. Deere may be the same. Dave
 

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Hi Dave:
Wow. That is really ingenious. I can't imagine how someone thought of it. At this juncture, I have decided that I don't need to replace the thermostat. My one test drive with the leaking radiator cap seemed to indicate that the thermostat is working. After I get the new radiator cap I am going to implement cheapsnake's suggestion of driving the machine and checking the temperatures with an infrared thermometer. If I get some indication that there is a problem with the thermostat I will replace it. That said, thanks to your dad, now I have a very cool new item in my bag of tricks.
 

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Hi all:
Got the new radiator cap on today. Ran it a couple of miles up and down the county road. The radiator fan cycled on and off a couple of times like it should. Apparently what cheap snake said that about that engine is true. It appears to run very cool. I had to run it up hill really hard to get it hot enough to make the radiator fan come on. Doodling along at about 3 mph, I never saw a temperature on the engine of over about 160° and never saw any temperature anywhere above about 190°. I do not see any leaks.

The only thing I don't have working is the brake lights. I think it is probably the brake light switch. According to the service manual, in order to get at that, I have to pull the cab, pull the hood, pull the seats, and pull the black shroud from under the seats. This is not going to happen.

I'm calling it road ready. The brakes still chatter at low speeds even with the new oil and the PEMO additive. Per one of my previous posts, the old transmission oil was absolutely horrific. I'm going to run it a few hours, drain it again, and put new oil in it a second time. The bottle of PEMO "friction modifier" that I got from John Deere specifies a treatment rate of 1 to 1.2%. The thing holds a little over a gallon, so I put 2 ounces in. I will try that rate again when I put in the new oil. If that doesn't fix it, I will try some more.

Very much appreciate all the help I received on the forum.

Best regards

Mike
 
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