Kubota Servicing 101: Part 3 – Cooling System

This article is the third in a series that covers off some basic servicing procedures for your Kubota. Earlier articles covered air and fuel systems. In this article we touch on your Kubota’s cooling system:

  • radiator cap
  • cleanable mesh screen
  • hoses (top, bottom and bypass)
  • radiator fins, body, shroud and fan blade
  • overflow tank and drain petcock
  • contents of the radiator

Radiator Cap
Your Kubota is designed to operate with a pressurized cooling system, same as you typically find on a car or truck. The pressurization raises the boiling point of the coolant so it’s important that it hold pressure.

Check the cap – it should be rated for 12 to 15 lbs of pressure. If you have a coolant pressure testing system, pressurize the cap and see that it holds at the indicated pressure. If it slowly drops, then replace the cap. If you don’t have a tester or access to one, then inspect the cap, its spring and rubber sealing gasket. If the gasket is torn, or as is often the case, chipped, replace it. If the cap wobbles or doesn’t seem to engage snugly with the neck of the radiator, replace it. It’s money well spent to prevent a costly engine repair.

Making sure the pressure on the rad cap remains steady

Making sure the pressure on the rad cap remains steady

Clean that Screen
Most B, L, L-1, Grand L, and M Series Kubota’s have a removable mesh screen installed in front of the radiator. The problem is, most owner/operators don’t even know it’s there. These screens are discreet and often just look like part of the radiator which explains why they are often not removed and cleaned.

The fine screening is designed to keep debris out of the radiator fins and its this screen that needs periodic cleaning and blowing out, particularly if you do a lot of mowing or rough cutting. The newer BX models are designed with the radiator mounted more mid-tractor and the fan blades direct air back through the radiator. This keeps the radiator and cooling system on a BX cleaner than earlier L Series Kubota’s.

To clean this screen, find the hold down bolts, loosen them off and withdraw the screen and frame. Using some air pressure, blow the screen out and blow off the exposed front of the radiator fins then reinstall. Simple!

What we are looking for when it comes to hoses is feeling around for any softness or mushiness – a weak hose. Push your thumb into the middle of the upper and lower hoses feeling for softness. The lower hose may have a coiled spring inside it, so workaround that. Twist and pull on the hoses slightly where they are held in place by the hose clamp. Any tearing? Do you hear ripping?

Test rad hoses by feeling for soft spots, twistly slightly and looking for tears or listening to ripping

Test rad hoses by feeling for soft spots, twistly slightly and looking for tears or listening to ripping

Early L-Series Kubota’s had fabric covered hoses. If your tractor still has these on the hoses, it’s time to replace them. The hoses in general should feel supple, yet firm. They should not have bulges or soft spots. If they look original and the tractor is 10 years old, replace them.

Don’t forget to take a look at the bypass hose if you have an L-1 or Grand L Series either. Those little 4″ long hoses can go bad too. Get down on the shop floor and look up from the underside of the radiator if your tractor has a drain petcock on the right hand side of the frame. Chances are there is a hose running along the inside of the frame rails from the left hand bottom side of the radiator to the back side of that drain petcock. Those who own an L1802, L2002, L2202 gray market Kubota will know how difficult this little hose can be to change out! Seems like Kubota had a hose and then built a tractor around it.

Belts, Thermostat and Water Pump
The fan belt is a fairly easy check over. Push down in the center of the belt to measure deflection. Should be 1/2″ or so of give. Tight, no slack. Roll the belt over and check the v-groove side for cracking and glazing. The belts should be replaced if you notice fraying, cracks or excessive glazing. If it makes noise when the tractor is running, replace it as well.

The belt is hard to get to so we are using a socket extension to test its deflection.

The belt is hard to get to so we are using a socket extension to test its deflection.

The water pump should be visually inspected for any leakage from either the pulley bearing area or from the gasket/front engine case area. On a Kubota you’ll know when the water pump or thermostat require replacing as the engine operating temperature will ramp up very quickly and you’ll be hemorrhaging coolant. Shut down and investigate ASAP!

Rad Fins, Body, Fan Shroud and Blade
Visual inspections here can really save on expensive repairs and down time and take only a few moments once or twice a season.

When blowing out the mesh screen from the earlier step, also blow out the radiator fins. Blow from the engine side to the grille or front of the tractor. Take a look at where the fins attach to the top and bottom tanks of the radiator. Corrosion showing here means a repair is looming.

The tanks of the radiator should be of normal size, not distorted or expanded which may indicate previous expansion freezing due to a weak coolant mixture. Grasp the fan shroud and make sure it’s firmly attached to the radiator body. Align it if it’s contacting the fan blade. All Kubota tractors employ a flex style white plastic fan blade. Visually inspect for cracks on any of the blades. Clean the fan blade if yours looks black!

Overflow Tank and Drain Petcock
Quick visuals are all that is required here. Check inside the overflow tank for sludge. Unclip the reservoir and clean it out if it looks ‘muddy’ in there. Top it up with new clean 50/50 coolant mix. Open the drain petcock (have your catch basin ready below) to discharge any rust or heavy deposits that have settled into the lowest part of the system, the drain. Removing these annually will keep the cooling system in top shape.

Open the overflow tank up and check for sludge or muddy coolant

Open the overflow tank up and check for sludge or muddy coolant

Radiator Contents
If your Kubota is operated in a warmer climate where the possibility of a freezing temperature is remote and you’ve been running water alone in the cooling system, now is the time to upgrade to a proper 50/50 glycol water mix. Why? Well it has a higher boiling point, has anti-rust properties, lubricates water pump bearings and is safer on gaskets than water alone. But it too must be changed regularly to ensure continued engine protection.

All too often in the service department we see needless upper cylinder head damage caused by overheating, porous cylinder head gaskets and blown expansion (frost) plugs. These are expensive repairs that absolutely could have been avoided by proper radiator cooling management. Those early Kubota L Series tractors had a whistle installed on the overflow tube to sound off like a train when the radiator was run completely dry. If you’ve ever heard that whistle think of it as the sound of money being spent in my service bay! Point being – don’t ever let that whistle blow.

Checking the coolant frequently is a good habit to get into

Checking the coolant frequently is a good habit to get into

Check the contents of the rad before operation each day. Kubota recommends an annual flush and refill of the cooling system. Don’t operate on water alone and don’t operate on straight anti-freeze/coolant. A 50/50 mix is recommended. If the coolant doesn’t look green, has a brown color or looks like mud, it’s been too long since it was serviced. Up the diligence here as this one is pretty serious.

Summary for Servicing your Cooling System

  • check radiator cap by seeing if it can hold pressure
  • remove and clean mesh screen in front of radiator
  • test rad hoses for softness and tears
  • test fan belt for deflection of not more than 1/2″
  • check fan belt for cracking, glazing or fraying
  • blow out radiator fins and visually inspect for corrosion
  • check overflow tank for sludge or deposits
  • make sure your radiator contains as 50/50 glycol water mix

Service Department Vic

Related Articles
Kubota Servicing 101: Part 1 – Air Filter
Kubota Servicing 101: Part 2 – Fuel Filter
Kubota Servicing 101: Part 4 – Oil Change
Getting to Know your Kubota’s Clutch
Forum: Service, Repair & Maintenance


  1. Geoffrey Said,

    November 10, 2008 @ 2:33 am

    Hi, I am on the process of buying a second hand farm tractor and after reading your articles I’ve finally decided to get a kubota brand, I’ve read your articles and learn alot from it. But never find any regarding TIPS and things to consider on buying a second hand tractor. Could you be kind enough to teach me some pointers, thanks in advance and more power!


  2. AK Said,

    January 14, 2009 @ 7:54 pm

    Good Stuff, I recently bought a B6100DT and your fuel bleeding article came in very handy when I ran the tractor out of fuel. The manual is good but comes no where near what you give us in your videos/articles.

    I am changing all the filters and fluids. Would do a video and article on changing the transmission and front wheel drive fluids? Also, the steering box?

    Thanks and much appreciated!

  3. Mr. K Said,

    January 14, 2009 @ 11:35 pm

    Hey there AK,

    Thank you for taking the time to post a comment and glad to hear that our fuel line bleeding video and article helped you out a bit. Regarding additional videos for changing transmission, front drive and steering box fluids – a great idea!

    The next time we setup for filming, we will cover off how to change these fluids as you suggest. I’ll write you a quick email to let you know that we have some new content. Thanks for the suggestion! Much appreciated.

    Mr. K

  4. jim turnage Said,

    April 10, 2009 @ 2:24 pm

    My L3130 has been stalling when I put it in gear. I have changed all the fluids and filters, checked the coolant and added injector adn carb cleaner.

    I notice there are two tubes going into the coolant overflow bottle. One hangs loose, connected to the bottle on one end and nothing else on the other. Is it supposed to connect to something or is it supposed to hang loose?

  5. Vic Said,

    April 13, 2009 @ 6:21 am

    Just like Elvis. “Hang Loose”!”

  6. mohomad bigi Said,

    April 21, 2009 @ 2:50 am

    i job meckanick farm machenery kubota

  7. Julian (from UK) Said,

    April 22, 2009 @ 2:17 pm

    Great article – I hope you do not mind me adding my thoughts and experiences – although based on my European specification B1750, I think some may be valid to US readers too.

    You state that the fine filter is in front of the radiator. Mine isn’t – it is behind the radiator.

    I think it is a case of blowers and suckers. Cars, for example, suck air through the radiator – the air comes in the front, goes through the radiator then over engine. When moving, the engine fan which is behind the radiator is not required (so is often electric or viscous coupled) as the air flows through with the movement of the car and a fan is not necessary.

    Kubotas (or at least my B1750) do not do these sorts of speeds and are what I term blowers. The fan is direct driven off the engine, but more important it works the other way, Air is pulled over engine (thus cooling it) then blown forwards through the radiator. The fine mesh is thus behind the radiator. I think Caterpillar crawlers are similar.

    I suppose the point is to blow through the radiator to clear any debris in the fins, the air jet should be in opposite direction to that of normal flow – so the debris goes back out the side it came. So, for my B1750 you blow from front of tractor, not the engine side as the article suggests.

    One other thing – I try and clean the fine filter off first with an industrial vacuum cleaner rather than using an air jet – I like the idea of sucking the debris up and capturing it rather than blowing it everywhere then breathing it in. Just me.

    I can confirm that the blocked fine filters will cause overheating if not kept clean! And it invariably happens when you are furthest from workshop / top-up water.



  8. Julian (from UK) Said,

    April 23, 2009 @ 12:16 am

    I should also have added that on hydrostatic tractors, there may be a second cooler for the transmission oil that also needs to be kept clean.

  9. Mike Said,

    October 15, 2009 @ 8:44 pm

    I have recently purchased my first tractor. It is a Kubota L2000. It is in great shape other than the brakes ( they are somewhat weak on stopping power). I was wondering if there is a u.s made comparable model that is the same as the “grey market” tractor i purchased (without knowing the trouble it would be finding info on it). I want to keep it serviced but don’t even know what i’m looking at! A service manual with diagrams, specs and fluid recomendations would be great if I could find one. Any ideas on what u.s model is the same as the L2000? Perhaps i could find a used manual on it. Thanks, Great site! Mike

  10. Bisbano Said,

    November 23, 2009 @ 6:19 am

    Wher exactly is the radiator petcock on the b7100 3 cyl deisel ayway, I don’t see it.

  11. Vic Said,

    November 23, 2009 @ 8:03 am

    Right between the frame rails at the front lower grille area, slightly to the left . Your operators manual covers this.

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