‘48 8n coolant Issue

I recently bought an 8n and it overheated a couple times
when it got over 100 degrees outside. I made sure the coolant
was just over the top of the radiator fins, tried richening the
mixture, ordered a jig to set the timing, made sure the belt had
proper tension. It didn’t have a thermostat so I figured it was a
good time to flush the coolant and install a thermostat with the
pointy end towards the radiator and installed close to the
engine block. I was able to only get a couple gallons of
coolant in so I figured I needed to run it long enough to open
the thermostat. After a bit of running time the fluid level rise
and it started pushing coolant out of the radiator. I checked
the upper hose and it was too hot to hold onto on both ends of
the hose. The lower hose was not nearly as hot. So it seems
my problem is worse than before flushing and installing a
thermostat. What am I doing wrong? Thanks for any help.
Oh- the temperature today outside was only in the low 90s
and the tractor was in the shade.

One thing I forgot to mention is when the tractor had overheated before, it was after running it for over 30 minutes.

The most common reason for an N to “over heat” is over filling the radiator. Only add enough fluid to cover the core. (check out tip # 24, below as well as tips 25 & 35) It is not actually over heating; it is just spewing out the excess water.

If the radiator is not overfilled, check for low coolant, a loose fan belt, debris in the radiator fins or a stuck thermostat. A bad water pump will usually squeak or leak. (If you ever have a water pump start leaking or making noise, replace it immediately. A N water pump will come apart & launch the fan into the radiator.) And, unless you have a new/rebuilt water pump from a reputable source, it could have impeller erosion. The pump will turn, it won’t leak, but it isn’t circulating water.

In order to have a stuck thermostat, you need to have one installed. Squeeze the top hose; if it has a t-stat, you can feel it. Sometimes (rarely) the t-stat can migrate in the hose & get stuck closed. Or, in an attempt to keep that from happening, some owners will put a third clamp on the hose & tighten it too much resulting in a stuck t-stat. The OEM top hose came w/ a non-adjustable ban to keep the t-stat in place.

The fan belt should have 1/2" of flex at the mid-point; no more, no less.

Unless you have a pusher fan, blowing out the radiator from the engine side is always a good idea.

If none of that works, you may need to flush the radiator & block.

Get a can/bottle of cleaner from the parts store.

Remove the t-stat from the top hose. Reconnect the hose.

Pour the cleaner in the radiator & run the tractor to operating temp.

Then, remove the bottom hose from the radiator, stuff a rag in the bottom radiator hose connection, & stick your garden hose in the top of the radiator. Turn the water on (reverse flush) & the water will flow into the radiator, then the block & out of the disconnected lower hose. Let it run until the water is clear. Then, check the radiator flow. Stick the hose in the top of the radiator; the water should flow out of the bottom w/o backing up in the filler neck. It should flow at 19.5 gallons a minute. Don’t forget to put the t-stat back in correctly!

Use 50/50 anti-freeze & distilled water as your coolant. The anti-freeze contains rust inhibitors, pump lubricant & raises the boiling point of the coolant.

If you do need to get the radiator re-cored, make sure you get the flat fin industrial core. Automotive style cores will clog up w/ debris very quickly.
75 Tips

On my 9n,while I had it split I decided to "rod out" the coolant channels in the block. The rear ones were blocked with a sticky goo that kept filling the small[3/8"+-] wire core brush I was using,so I filled the cylinders with oily rags and pressure washed the block where the water circulates[or should] around the cylinders. This resulted in lots[and I do mean a lot!] of the goo coming out. After getting the motor together and running,the block ran at about 180* and the heater hose was about 170* using a laser thermometer. I'm not saying that this is your problem,but it's a possibility.

(quoted from post at 11:24:59 08/10/20) ...

If you do need to get the radiator re-cored, make sure you get the flat fin industrial core. Automotive style cores will clog up w/ debris very quickly.
75 Tips

Click to expand...

Hmm, I just bought the 8N radiator this site sells, but not the 'authentic one'.

is my old radiator worth something to someone who wants to recore it? it wasn't leaking, but it wasn't cooling very well, seems all clogged up.

Fan belt tension is a good check for overheating issues but I don't understand your thinking on why you needed to set the distributor timing - one isn't related to the other. Did you install the distributor correctly with offset tangs and cam on engine? Back to the radiator. I think you should have taken the unit to a reliable radiator shop and have it boiled and tested there. How's your water pump? Time for a rebuild? You need a thermostat. BTW, model year is not important. All N's used the 4 PSI Radiator since '43.

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Tim Daley(MI)

Thanks for the feedback from everyone.

Regarding the timing, I've read in several places that retarded timing can cause overheating.
The belt tension is good and the belt is the correct size. The water pump doesn't make noise, though I've not taken it off to see if the impeller is in good shape.

The thing I haven't figured out is why did the tractor run for close to an hour in extreme heat before boiling over and then after flushing the radiator and engine and then installing a thermostat and new coolant it started pushing out coolant within 5-7 minutes. And I wasn't able to put in more than 2 Gallons of coolant. something changed because of what I did and I'm stumped. The thermostat is facing the right direction. Is it possible it's just a bad thermostat? I might pull it out and run it to see if that changes things.

No doubt the radiator probably needs to be worked over and probably the ports in the engine need to be cleaned out. I'm learning that I should have done my homework better in this tractor before I bought it.

You can test your thermostat in a pan of water on the stove and a thermometer (candy, meat). Does you tractor have a shroud around the fan? If the new thermostat is good, then I would be looking at the water pump, the radiator and a good block flush.

(quoted from post at 05:24:31 08/11/20) Fan belt tension is a good check for overheating issues but I don't understand your thinking on why you needed to set the distributor timing - one isn't related to the other. Did you install the distributor correctly with offset tangs and cam on engine? Back to the radiator. I think you should have taken the unit to a reliable radiator shop and have it boiled and tested there. How's your water pump? Time for a rebuild? You need a thermostat. BTW, model year is not important. All N's used the 4 PSI Radiator since '43.

Click to expand...

well, since I was in there, I pulled the distributor to clean the outside, and check the points, and low and behold one of the screws that holds the points to the plate was stripped, the tiny cutter pin that holds the points rocker onto the shaft was sheared off, and the points were all gummed up with spider webs, even after cleaning, I couldn't get them to stay at the right 0.015 gap, so I got a new points plate with points, installed, gapped, and timed it. I don't have the jig, but I used a straight edge and my DVM in beeper mode, and eyeballed the 1/4 inch, doing it over and over til it was right...

Next up, I need to get the hood bolted down (screw holes aren't readily lining up, will take a helper probably), then I can fill the coolant, and resume with setting up the carb which I think was running way too rich based on the oily black deposits on the old plugs.

re reliable radiator shop, I don't think we have one here in santa cruz anymores, and if we did, the labor would likely exceed the cost of the replacement

I failed to answer your question about the shroud and it does have one. I’ll try that thermostat test. I didn’t run cleaner through the system so when I pull out the thermostat I’ll do that and flush it and put in new coolant.