8N Overheating

Have mowed grass and bush-hogged pastures nearly weekly with my early 8N (front-mount, 12v, EI) this summer, without difficulty or issues. Yesterday, about 1 1/2 hours into a 2 hour job, with temps in the mid-80's (not as hot as some days), it began spewing steam from the radiator cap overflow hose that terminates underneath. Driven to the barn without problem and shut down. After cooling off, the 50:50 Prestone:Water mix was still above the fins and about 3 below the top of the radiator..., which is where I keep it, so little coolant was lost and no fluid was dripping from the water pump. Fan belt is normal and alternator is charging, so no loose belt issue. This morning checked: started normally, but after warming up no turbulence could be seen in the top of the radiator and after a few more minutes began steaming again out the top of the radiator (cap off).

I would think a stuck thermostat (which has probably not been touched in many years), but I don't know why or how it would cause this 1 1/2 hours into use and I think it would have overheated sooner if it was stuck closed at the start-up. Can a water pump quit circulating without leaking? Someone has probably had this problem, what did it turn out to be? Trying to avoid taking off hood if I can, since back problems don't allow me much lifting strength these days.
 
Bush hogging puts a ton of debris into the radiator fins. Try blowing out your radiator with an air hose. If your fan is a pusher, blow it out from the front.
 

#1 rule bar none.

Coolant absorbs the heat air takes it away... Log that in its a hard fact never forget it as you work thru the issue.

I have been bit by the belts OK I would like to see a pix of the alt/belt set up...

Next is the radiator fins free of debris.

The next fact you have not proven its overheating yet.
 
The main causes of radiator overheating are: overfilling coolant level, under filling coolant level, stuck or lack of a thermostat, inefficient fan blade operation, and plugged fins or leaks obstructing air flow. How old is the radiator? Have you ever had it cleaned and serviced? Might be time to pull Thermostat, test, and replace if needed. Is Thermostat mounted correctly with pointy end towards radiator? Is the band or tie wrap on hose keeping the unit in place? Pulling the hood is time consuming job but sometimes you need to bite the bullet and do what is needed. Good, old time radiator shops are getting hard to find.

Tim Daley(MI)
 
This problem occurred while using the finish mower, and there was no debris in the radiator fins. I have had in past times lots of fall flower debris and other stuff in the radiator fins when bush hogging, so I know when and how to clean that out when needed. That is not part of this issue. And the radiator was cored and boiled once since new and there is normally good flow in the system. Thermostat has been working normally, to my knowledge, for many years; and fluid level is the same it has been also for years without issue and no overheating. Nothing has changed until two days ago when it steamed out the overflow hose, so something has changed. I just wanted to know if water pumps could fail (stop circulating) without leaking or if a thermostat could close suddenly while in use. Never had that to happen, but there is a lot more experience here than I will ever have alone. Hobo, don't know what the picture shows you other than the belt being mildly frayed but no slipping is occurring and obviously nothing has changed in its set-up. Don't know how you define overheating, but when steam started coming out I headed to the barn since that had never occurred before. Are you saying there might be nothing wrong?
cvphoto95821.jpg
 
This morning checked: started normally, but after warming up no turbulence could be seen in the top of the radiator and after a few more minutes began steaming again out the top of the radiator (cap off).

Pretty much indicates bad thermostat, water pump, cracked head, or bad head gasket. Take your pick.
 
Jim in Western MI,Your belt is badly worn on the sides and loose also.Replace it with a new one the correct with and tighten it up that will help the fan cool it down.
 
Jim, Couple of things If I may .....

Reason I mentioned about blowing out the radiator with air is because I have seen what looks like a clean radiator, but in reality can be plugged almost completely with dust that has turned into pellets inside the fins. I've seen this when an original radiator is removed for thorough washing and cleaning.

As far as a water pump looking good, but not circulating coolant - I've never seen it in a lifetime of working on tractors, but I suppose anything is possible.

I have seen thermostats fail in both the open and closed positions though. Not common, but I've seen it.

Hard to tell by the pic of your fan belt, but the fact of it being frayed makes it look a little loose to me. Hard to tell though, again, with just the pic.

Hope you find and resolve your problem.
 
Here is an example of what thermostats can do. The year before last I was using my NAA and it overheated like yours did but never did it again. Then last year I was mowing with a rotary mower and noticed that the engine never got up to normal temperature. I replaced the thermostat and now it's back to normal.
 
See rule #1 that belt looks like chit I would wager its slipping... That means air is insufficient to remove the heat...

I would wager engine off you can grab the fan and turn it if so the issue is looking you in the eye... A lose belt will also undercharge the battery it will get you in time...

Heating is when it boils all water/coolant steams when its gets hot... I would say you were getting to that point tho on the ragged edge. No temp reading no logic to work on other than your gut...

Take care of that belt all other questions are mute at this time...

I will never understand how over filling the radiator will make one run hot... They need to get that out of their head... Its very misleading...
 
New belt installed and securely tightened. No change, after about ten minutes of mowing, steam out the overflow tube and around the radiator cap. Seemed worse going uphill back to the barn. No water in the oil, no oil in the water; so head gasket and cracked head at least temporarily ruled out. Will be going for stuck or partially opened thermostat next.
 
(quoted from post at 19:55:12 07/28/21) New belt installed and securely tightened. No change, after about ten minutes of mowing, steam out the overflow tube and around the radiator cap. Seemed worse going uphill back to the barn. No water in the oil, no oil in the water; so head gasket and cracked head at least temporarily ruled out. Will be going for stuck or partially opened thermostat next.

Jim, I hope the thermostat does the trick for ya. If not , I do think I read here once of a impeller on a water pump being loose and slipping, but I could be mistaken. Good luck and thanks for the update.
 

A N is extremely EZ to check the operation of the thermostat. The radiator fill neck is located at the outlet from the thermo. What we don't know is what's the temp below the thermo. Without indicators tools and such its a judgment call.

To start diagnostic you need a bone cold engine the coolant set to the proper level, fire it up and let us know the history of coolant flow from the thermo as it warms up thru a heat cycle. A temp gauge even a meat thermometer will take the guess work out of it...

Keep in mind an OEM thermo starts to open at 160 (starts not fully open) its not fully open till 185/190. Once it reaches 185/190 it should be able to maintain a constant temp if not then something is suspect.

Thermostats in general either work are they don't use your window (fill neck) to make that call... Count you blessings unlike most machines its laid out well... Another rule I can not diagnose it HOT I have got to start out with it COLD and go thru the steps of how we got to this point.

Proper coolant level and air flow is always on my mind.
Coolant absorbs the heat air takes it away : )
 
Can a water pump quit circulation? Yes the impwller can break lose and not turn. In thissituation it is trying to just thermosifon the coolant like older engines designed without a water pump. Add a pump and will run cooler.
 

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