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I started a thread last year about this time about my 721d over heating and trouble shot what everyone could think of and never found a fix. The shop I bought the mower from went out of business at the end of last years season so I am still battling the same problem however I noticed something when I was cleaning off the radiator while it was cooling down the last time it over heated.

The top 1/3 of the radiator is about 4 times as hot as the bottom 2/3. So, I'm guessing that it is full of jukn and needs to be cleaned out. I am by no means mechanically inclined but thought maybe there was a way to flush it without needing to take it off the mower. I've flushed a truck radiator before but dont know if there is any difference in a deisel that I should know.

If flushing doesnt work how hard would it be to take the radiator off? I'm sure the mower shop would charge an arm and a leg just to take it off and run it down to the radiator shop.

Thanks all and any opinions/suggestions would be great!

Flush it like any radiator...
It may have something restricting the water flow, but the top of a radiator will be the hotter end... Water comes in the top from the engine, then cools down and exits the bottom back to the engine...

Is there a shroud around the fan to insure adequate air flow through the radiator...
Is there a good pressure cap on it?
really shouldn't be hard to keep a diesel cool.. :smile:KennyV

might help too if you blow the rad. fins from behind using compressed air.I always do this after each mow and a considerable amount of dirt and chaff comes out...russ

KennyV said:

Flush it like any radiator...
It may have something restricting the water flow, but the top of a radiator will be the hotter end... Water comes in the top from the engine, then cools down and exits the bottom back to the engine...

Is there a shroud around the fan to insure adequate air flow through the radiator...
Is there a good pressure cap on it?
really shouldn't be hard to keep a diesel cool.. :smile:KennyV

Click to expand...

The top is so hot that you cant touch it while 2/3 of it down is cool enough that you can keep your hand pressed up against it for as long as you want.

Yes
Yes
And I know and have been trying to figure it out since the first time it over heated after purchase.

173abn said:

might help too if you blow the rad. fins from behind using compressed air.I always do this after each mow and a considerable amount of dirt and chaff comes out...russ

Click to expand...

Yeah, like I said I had a thread last year at this time and trouble shot a bunch, it was a 4-5 pages thread.

I checked hoses for blockage, radiator cap, blew out radiator from both front and back which I do anyway, and then I noticed the difference is temps of the actual radiator the other day.

That difference in temperature shows that the radiator is transferring heat.
The inlet will be at engine temperature, around 180 to over 200 degrees, way too hot to touch with your hand... Have you actually measured the temp at the inlet & the temp at the outlet?
also, Check the Water flow rate, You can get fairly close using a garden hose running into the top hose connection- and measure the quantity that free flows out of the bottom... Or just remove it and let your rad shop check it out...
I do remember you having this problem last year...
Is there any chance that someone replaced the original radiator with a Smaller BTU capacity rad, prior to you getting this... ? a radiator meant for a smaller engine could look to be the same size, but will have fewer rows of cooling tubes.... :smile:KennyV

I am new to this group and joined for this very reason. I also have a 721d grasshopper with a overheating issue. the temp at the top of the radiator measures 190 and the bottom 170. I have a friend with one who has the very same problem. I wonder if some early models came out with undersized radiators or could there be a head gasket issue which causes excessive heat into the radiator but does not show up in engine performance.
Ron W.

You could take the radiator to a radiator shop. They would have the tools and experience to be able to take the tanks off and "rod" out the radiator core.

If it is not repairable, they would be able to find a new core for you.

WELCOME to LMF, Ron W.....
20 degree temp drop is a little anemic... check that you do not have an air flow OR a water flow problem...
Any dirt coating the cooling fins will prevent heat transfer to the passing air, belt slip or or no fan shroud....
Deposits inside the radiator will slow heat transfer, thermostat not fully opening, collapsing Lower radiator hose or slipping belt on the water pump will reduce the water flow rate....

Diesel engines don't need a Lot of radiator but it is possible to overload the factory radiator... My ZTR mower with a 4 cylinder Kubota can overwhelm the smallish radiator if I push it hard... never have ran out of power but I have ran out of cooling when the ambient temp is over 100 degrees and I get into a hurry... :smile:KennyV

Thanks for the replies, both good ideas. I have cleaned the radiator and tightened the belt to the pump but a check of the t-stat sounds like the next step. I really like the power this diesel has but the high water temps cancel that out.
Thanks again,
Ron W.

You have recieved a lot of good thoughts of how to solve your heating problem. In my opinion the first should be checking for sure that it really is heating up and not just a faulty gauge or sending unit. This can be checked by geting the MFG temp for mid range then remove the sending unit placing it in a bowl of heated water of a know temp using a second thermometer to check the calibration while still connected to the gauge. I have a 721 Grasshopper gas and even during this hot summer on a 100 dg. day it would rarely get past mid range never out of working range.

Its been a while since I posted but did finally manage to figure out why the mower was over heating. A engineer from Paducah KY had been informed of the problem and he managed to fabricate some kits to help the problem. The shroud/screen that covers the radiator doesn't keep clippings out of the fins so it continues to build up with small debris over time. I bought my mower used and was informed to blow air through the radiator by members here and also from my local repair guy. I was able to see particles coming out of the radiator after mowing when I blew it out but had NO idea just how much junk was trapped in there. I literally ran water through the radiator for an entire day before all the particles were finally removed. It has never over heated since the long thorough exterior cleaning. Blowing it with an air hose after a couple of sessions.

The engineer basically made three metal sheets that help keep clippings from entering between the screen and radiator. One piece on each side and one that slides up under it that is attached to the bottom of the seat. The kit hasn't been that helpful on windy days as I still have to clean off the front of the radiator after a few acres but the temp goes down immediately after rubbing the clippings off.

So its just a design flaw with the screen that doesn't keep everything from being sucked into the fins. An extremely good cleaning took care of the problem along with regular blowing it out throughout the season has kept the problem from returning.