800 Very hot exhaust, temp gauge normal, sputtering

I was attempting to cut hay with my Ford 800, and made it only once around a small field.

The tractor started sputtering, and was losing power, so I stopped. I dismounted from the left side and noticed that the exhaust system was much hotter than usual. I'd been monitoring the temperature gauge while I was cutting, and it vacillated between the center and just right of the center in the green (but always stayed comfortably within the green zone).

The valve cover was too hot to touch.

The radiator seemed hot, but not as hot as the valve cover.

The muffler was discolored (I assume from heat).

I checked the coolant level before I began, and then again after it cooled down, and it was still full.

So far I've checked the timing, points, cap, rotor, plugs wires, and plugs. I rebuilt the carburetor (I had the kit and was intending to do that before I started cutting). I also checked compression, and all cylinders were good and within 5 pounds of each other.

Everything looked good except the point gap was slightly off, and the coil was slightly out of spec on the secondary winding resistance. I set the points and swapped out the coil with a coil that was withing specifications.

The outside of the carburetor was dirty, but the inside was surprisingly clean.

Nothing I've done has changed anything. It runs fine at idle. Anything over idle and it gives a sputter or two every 10 seconds or so, and the exhaust gets abnormally hot. This is with it parked, and under no load.

My latest thought is that perhaps my temperature gauge is faulty, and I have a non-functioning, or barely functioning thermostat. I'm not sure how that would cause sputtering, but I'm running out of ideas.

I'd appreciate any thoughts on this.

I forgot to mention that the fuel in the tank was bubbling/simmering right after I stopped cutting.

Also, I checked the fan belt, and radiator fins. The belt was fine, and the fins were almost perfectly clear.

Been there, experienced that. Did you check fuel flow when it was very hot?

I am not an expert - so my insight is questionable but i can relate.

Temperature gauges that i have bought didn't seem reliable after a year or so.

My first thought is a failing thermostat. If it's possible to get at it.... put it in a pan with water and
turn the burner and see if it opens as the temp rises.

After verifying static timing, verify that the centrifugal advance mechanism is functioning properly.

If the muffler heat shield and fan shroud are not in place, install both and avoid gasoline with ethanol if possible.

Dean

R u running points? And have u changed the condenser?

Get yourself one of those little infrared thermometers and find out what your actual conditions are then take it from there.

Is this the same tractor that you had the exhaust valve insert come loose in before? and had a crack in the head?..if so that
might be the problem.

Murray-
I did not check the fuel flow when it was hot. I've theorized that if the fuel in the tank is boiling, the fuel in the line (which runs close to that overly hot muffler) would not be completely liquid.
The first thing I'm going to try is Dean's idea of making sure the timing is advancing as it should with increased RPM.
If that doesn't prove to be the issue, I'll pull the thermostat and give it the hot-water test. Thanks for the idea.

Dean-
I will check the timing advance. Thank you for that idea.
The fan shroud and muffler heat-shield are both in place.
I don't know where I could get gasoline without ethanol. (The ethanol has turned the hood of my tractor black.)

Showcrop-
I've been wanting to get an infrared thermometer anyway. Now seems like a good time.

Murray-
Yes, it has points. The condenser has probably about 100 hours on it.
That made me realize that I didn't actually know what the condenser does. This thread helped me with that: https://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=nboard&th=500667

Marlin-
Wow. You have an amazing memory. Yes it is the same tractor. The head being cracked was the assertion of the surly guy at the first machine shop I visited. He hadn't even looked at the head. The second machine shop actually checked the head (with magnaflux) and found no cracks. That's the shop that replaced the seat as well.

if the gas is getting hot in tank your in a dangerous situation..dont do anything else...you better have a professional or dealer
at this point. have them check to make sure the tank is not getting hot from a failure of the heat shield ...have them remove it
and inspect it n for holes or other problems...heat could be getting past it for some reason...very important...they have to make
sure the heat from the exhaust IS NOT blowing heat on any part of tank...or lines ...its not worth blowing yourself up over the
problem..at this point only a professional SHOULD work on it...boiling gas is a dangererous situation...your dealing with
gas...stop and let a professional work on it..playing with the timing could cause a backfire and your going to get hurt....JUST
have a professional look at it..

if the gas is getting hot in tank your in a dangerous situation..dont do anything else...you better have a professional or dealer
at this point. have them check to make sure the tank is not getting hot from a failure of the heat shield ...have them remove it
and inspect it n for holes or other problems...heat could be getting past it for some reason...very important...they have to make
sure the heat from the exhaust IS NOT blowing heat on any part of tank...or lines ...its not worth blowing yourself up over the
problem..at this point only a professional SHOULD work on it...boiling gas is a dangererous situation...your dealing with
gas...stop and let a professional work on it..playing with the timing could cause a backfire and your going to get hurt....JUST
have a professional look at it..

Won't running the engine too lean cause overheating? Just a thought.

A little.

Dean

Thank you for your concern Marlin, but I disagree with your assessment of this situation. I believe this is an issue that I can safely resolve myself, with the help of contributors to this forum, but without taking the tractor to a "professional".
The fuel got that hot when I was cutting hay. I let it cool down before trying to work on it. Perhaps I should have mentioned that I am not letting the tractor get even close to that hot while trying to fix the issue.
Concerning the heat shield, I recently had the tank off to replace the o-ring on the shut-off valve (it had started to leak). I examined the heat shield at that time, and it is in great shape (though the paint has faded a bit).
I agree that there are times when going to a shop is really the only prudent choice. In my experience, however, that has always involved needing specialized equipment that shops have: equipment that is too expensive for me to justify acquiring.

Thanks Glen (and Dean). I'll check on that too.

(quoted from post at 11:04:23 06/27/19) Thank you for your concern Marlin, but I disagree with your assessment of this situation. I believe this is an issue that I can safely resolve myself, with the help of contributors to this forum, but without taking the tractor to a "professional".
The fuel got that hot when I was cutting hay. I let it cool down before trying to work on it. Perhaps I should have mentioned that I am not letting the tractor get even close to that hot while trying to fix the issue.
Concerning the heat shield, I recently had the tank off to replace the o-ring on the shut-off valve (it had started to leak). I examined the heat shield at that time, and it is in great shape (though the paint has faded a bit).
I agree that there are times when going to a shop is really the only prudent choice. In my experience, however, that has always involved needing specialized equipment that shops have: equipment that is too expensive for me to justify acquiring.

Click to expand...

Brett, the other side of this issue is that the likelihood of finding a "professional" that know anything about 65 year old tractor is remote, and the unfortunate likely scenario, is that an uninterested 19 year old will be assigned to it, if you take it to a dealer. You are better off and safer to do it yourself.

While adjusting the load screw a little
richer will help a little with the heat
and power I don't think it will solve
your problem. Valves a little too tight
can hurt also. Ignition timing (advance
mechanism) usually results in poor
performance and engine heat along with
the excessive exhaust temp. To me it
sounds like an exhaust blockage is most
likely. Muffler stopped up or exhaust
manifold / gasket does not match head
ports.

I finally got back to this issue.
Dean was right to suspect the advance mechanism. It seems that was/is the problem.
I checked the timing at the three RPM points, as suggested in the manual. The timing was advancing with RPMs, but not nearly as much as it should.
This evening I set the timing at roughly where it should be at working RPMs (where the PTO speed is 540).
After doing that I cut grass (with a finish mower) for a little over an hour, and the engine ran cooler and better than it has in years. The exhaust temperature seemed to be normal.
I cleaned and lubed the weights, but I that did not change the sluggish advance.
-Brett