2006 RTV900 coolant leak

a hole in the thermostat will have no effect on cooling but will dramatically affect pressure balance. there may be an air bleed plug in the thermostat housing below the thermostat for this reason. if you run the machine with air in the system it is likely to cook the head.
 
While there are some significant differences with which I am not familiar between the RTV900 and the RTV-X900 that I have... I thought I’d mention the problem I ran into similarly with my X900 cooling system.

I found a small leak beneath the drivers seat which proved to be where a rubber hose clamped to a metal pipe. I removed the clamp and cleaned corrosion off the pipe and reassembled things .... then went to refill the coolant. THAT’s where a problem developed:
I refilled the radiator and noticed the overflow reservoir was still full so I thought everything was OK. But. NOPE. It overheated very shortly and when I rechecked the radiator it’s tank was empty AND the overflow reservoir was also!

I had to add almost another half gallon and the reason I was puzzled was because prior to the work both were full, and I caught ALL the drained fluid and was able to pour it back in which gave the impression all was fine.

BUT... I did not know about a “vent hose” which is equipped with a plastic valve for the express purpose of venting air out of the system after it’s been opened for service.

If your system hasn’t been completely re-filled you’ll likely know it shortly because it will overheat. This can damage the head gasket and perhaps even crack a head...so immediately shut it down if it does overheat and let things cool off before opening/re-filling the system. I’ll try to find that other post where I showed the vent hose location and come back to edit this post with a link to it.

Here’s the thread: http://www.nettractortalk.com/forums/showthread.php?t=17953
 
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Thanks for the tip about the vent hose. In the thread you linked, others with a 2006 RTV900 said they don't have one as described, but I'll take a look anyway. I did try running it with the front wheels elevated and the radiator cap off and I was not able to get any more coolant in. I called the Kubota dealer and one of the service techs told me they use a vacuum system when refilling coolant as it is hard to get all the air out. I guess the next step is to drill a hole in the thermostat as aurthuritis suggested.
 
Well I'm still stumped. I took out the thermostat to drill that hole only to discover it already has one. Then I looked at the parts diagram on Messicks and you can see the same hole, so using that as a way to bleed air seems to be the design. But I'm still left with the question of why I can only put in half of the capacity of coolant I should be able to. Do I just have a bad radiator full of plugged tubes and rust? It stays cool, but I only go on very short trips. Using the plow this winter should tell me whether I have a problem or not I guess.
 

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I went back and looked at all the threads in this post and I don't see if the block was drained. If not, there's a large amount of coolant/water in there. That may account for the low amount of coolant you can add.

Before you go any farther, be sure you know the concentration of antifreeze in the system. A simple ball tester from the parts store should do it.

If the concentration is low, I'd drain what I could again and add as much 100% antifreeze as I could and test again. If it's close I'd drive it and see what happens as long as you had washed out the radiator.

I don't recall your location but the antifreeze concentration is not only important to stop freezing but also for corrosion control as you can see from the condition of your system.

If you want to go further, the radiator should go to a proper shop for cleaning and repair.

I'm hopeful you have solved the problem with the steps you have taken so far.
 
Each time I have drained the system I did it just as described in the manual. Open the drain valve on the bottom of the radiator and remove the radiator cap. I have done it both with the rear wheels elevated and with all four wheels on the ground. Neither the owners manual or the service manual suggest any other steps that I am aware of.
 
dennardo said:
Each time I have drained the system I did it just as described in the manual. Open the drain valve on the bottom of the radiator and remove the radiator cap. I have done it both with the rear wheels elevated and with all four wheels on the ground. Neither the owners manual or the service manual suggest any other steps that I am aware of.
Click to expand...

When my RTV900 radiator was replaced I filled as you describe. Drove it around for about 15min. then topped it off. Was able to fill to spec.

Since the coolant was crappy when flushed the radiator is probably plugged. When removed the rust could be heard with a shake.

One site lists the new net weight at 4.7 lbs. Maybe weigh yours to compare?
 
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I have let it run at least twice that long after filling and never been able to get any more coolant in. I'm pretty convinced now that it is probably the radiator, but I sure don't want to go back in there and replace it right now, especially since I've never had any overheating issues. I think I'll just see how the winter goes and replace it if I have to.
 
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