D15 Running Hot

I have a D15 Series II. Within the last few years, I have had the radiator professionally repaired and replaced the water pump. My temperature gauge is brand new.

When running the tractor by itself, the temperature stays within an acceptable range. Recently, I started using the tractor to pull some choppers. When pulling the choppers, the temperature increases rapidly and I have to shut it down.

Since everything else was relatively new or updated, I thought it might be the thermostat. After removing the thermostat housing, I discovered that there was no thermostat. I had bought one online before starting the job, but the thermostat I bought appears to be to small.   It will actually fall in the hole on the engine. Nothing else came with the thermostat.

I read a similar post on this forum where someone else discovered there was no thermostat. Why no thermostat? Is this contributing to the overheating problem? What does the correct thermostat look like? Thanks.

It is a small thermostat, it sits in place on a gasket (see the AGCO parts book website).  A 180 degree thermostat would be best to use.
Some tractor owners have been known to do strange things.  Removing the thermostat is one of them.  I was always under the assumption that removing the T stat would cause the engine to run cold. Can't explain why it would be hot.
You said the rad was professionally repaired, but was it cleaned and boiled out at the same time?

They can run hot without a thermostat, because the coolant circulates too fast through radiator to take the heat out of coolant.   MACK

if the timing is correct and you get a thermostat in there and it still runs hot, then it is kind of a crap shoot.

May be time to have a flow test done on the rad.

Just a thought, I bought a used rad for mime and good thing the shop did a flow test on it before working on it. They said it was way below spec and that got me my money back.

good luck

Mack is 100% correct. Removing the thermostat will actually make the engine run hotter. Why? The thermostat is in the system to slow the coolant down, so as it passes through the Radiator, it gives the fan & radiator the chance to do their job which is to cool down that hot coolant before it returns to the engine block. Removing the thermostat increases the heat because as Mack mentioned, the coolant will move way to fast through the Radiator for the Radiator and the fan to do their job in keeping things cool. Hot in and hot out doesn't make cool. It makes the coolant HOTTER. In some applications, a 195 thermostat works better than a 180 because it slows the coolant down even more in order for the Radiator to do its job. The Radiator is a heat exchanger. The slower the coolant through it, the better the cooling. Of coarse, like anything else, the Radiator, fan, and fan belt need to be in tip top shape for everything to work at peak performance. That also includes the water pump also... HTH
Steve@B&B

Edited by Steve in NJ - 09 Jun 2016 at 8:09am

Like the guys are saying you need to run a thermostat to keep the engine cool, now if the thermostat will not open then you can break the center out of it put it back in just to run the tractor to get the job you are doing and then get a new one and install it, but don't just knock the center out and run the tractor that way it will not control the temp right in all weather.   

tbran wrote: timing can be an issue on the G160  too fast or slow will affect temp

Second on the timing issue! Saves head gasket too! Tracy

Test your new thermostat with a cooking thermometer and hot water to be sure it opens correctly. Don't use that cooking thermometer for cooking after that, antifreeze remains are unhealthy to ingest.

Then be sure the fins on the water pump impeller are still there. When they rust off or the impeller splits (usually a press fit on the shaft) water won't get moved. If the pump is pumping good, the radiator top tank level can rise a little with the engine running fast.

Gerald J.

How many blades are on the fan? We have 3 D15's 2 have 4 blade fans and 1 has a 5 blade fan. Didn't they put 5 blade fans on D14's to help cool them down? Andy

Is it true the thermostat's flange diameter is smaller than the hole in the cylinder head?
The picture in the parts books is nice, but you can't tell sizes, what slips over what.
And since we know it has been buggered with (no thermostat) the poster has a right to be concerned. What if they sent him the wrong thermostat, what if the cover gasket
is wrong or homemade.

I think the function of the bypass hose is to bypass the thermostat with some coolant.
If we called it the thermostat bypass hose I don't think you would now be worried on that point.

Is it possible that the lower radiator hose is collapsing from the suction? On large cars they put a support spring in that hose, but I don't see that so much on the short small tractor hoses.

Get an original or copy of the Allis-Chalmers service manual. I have them for all my stuff.

I am trying to remember when I changed the thermostat on my D15 years ago, it definitely was smaller and I did assemble it according to the parts book.  I just cannot remember the sequence that I did it in.  The small size did scare me in the beginning too!


Edited by DSeries4 - 09 Jun 2016 at 9:14pm

All the theory is correct, however I have pulled the guts out of several fork kifts,  abd D15's on grain augers. Some had thermostats some did not.  IF the Radiator is clean, he fan / alt belt is not squalling, the timing is right and the carb is not set too lean, they do not run hot.  Ge the unit hot and shut it off then recrank, if it 'kicks back' it is timed too fast. IF it  does not have a slight resistance advance a tad at a time till it does then back off a degree or two. Too much advance and kickback  will break the nose off the starter - beware.    Now open the throttle to high idle, screw in on the main load jet til ti starts to lower the rpm, then back out on the main load screw till it smooths out  then add a half turn more,   I also always check for fuel flow by backing out the main load screw more and watching for black smoke indicating a rich condition.  If you can't do this you are not getting enough fuel.

Thanks everyone. Looks like I have some work to do. I will let everyone know if the thermostat turns out to be the issue.

My dads D/14 was an eailer 57 and they did a upgrade on it . Changed fan to five blade , put chain on snap coupler release,push button on switch , filler cap on lift and maybe more.