Overheated Robin EH72-FI (28 hp) in PT-425 solved

[Marks481]

If what I am saying is correct, then I would try blowing air outward with both fans. Air will then come into the engine compartment from many areas.

+++1. You will get much better results blowing air outward. Heat rises, so the fan will be exhausting hot air and cold air will come in lower behind the engine where it does the most good. I put my side fan so the edge of it just overlaps where the exhaust manifold is. When the engine is hot, the output of that fan feels like 120F or so.

 

[BobRip]

+++1. You will get much better results blowing air outward. Heat rises, so the fan will be exhausting hot air and cold air will come in lower behind the engine where it does the most good. I put my side fan so the edge of it just overlaps where the exhaust manifold is. When the engine is hot, the output of that fan feels like 120F or so.

That's a good location since your are exhausting from the hottest part of the system. That is standard good air cooling practice.

 

[joshlee]

I tried to get that exhaust header package and I'm coming up empty? So, Im having a bike racing shop nearby make me a custom header pipe to fit on this muffler, after carefully, taking allot of temp readings at different locations on and around the motor. I'm thinking about mounting it where I'm holding it in this picture. Maybe even finding a piece of schedule 10 aluminum pipe to put around it for a heat shield? Maybe put heat wrap on the header?

I wouldn't say that. The PT422/425 runs hot, but doesn't normally shut down because of temperature. I have spent a couple hours bush hogging 12-18" grass in a pasture with no ill effects.

But that isn't stopping me from trying to make the machine run cooler. So I too have insulated the exhaust manifold, added an auxiliary fan to the side, relocated the fuel pump (stock fuel mechanical fuel pump in my model was mounted on the left side of the engine, at the height of the muffler which was about 4" away from it.... just asking for vapor lock, although I can't remember ever having a problem with that). Latest action was swapping out to a new exhaust manifold and muffler (following KMAs and Kent's lead). Less backfiring on shutdown, but my uncalibrated eye says it really isn't running any cooler.



I think you are right. I have rerouted my fuel hoses to run them far way from the exhaust manifold, but I still get bubbling in the fuel tank from vapor in the gas lines after I shut down from a long session of mowing. My fuel filter and fuel line is resting on top of one of the hydraulic pumps. Looks like time for a little more re-arranging.

 

[Kent]

My only thought is to move it further back...If you park your tractor and let it heat up, you will find that the tire rubber starts to get very soft like it will catch fire eventually! Plus you want smooth curves on that new pipe, which will push the muffler either up or back anyway.

 

[Marks481]

I'm thinking about mounting it where I'm holding it in this picture.

Don't do it. That is where I put my last muffler, and the exhaust fumes made it somewhat unpleasant to drive in the summer.

This time around, I installed the muffler like KMA and Kent did. Much better.

I like the idea of the heat shield. Been toying around with it for my installation, since the tub next to the muffler does get hot (and that muffler does have a heat shield on it already).

Quick cruise around the internet, and it does look like this particular version is now discontinued. Bummer.

Jack's Small Engines will sell you the exhaust header (PN 263-34101-A1) for $130, but doesn't carry the complete kit anymore.

Robin/Subaru EH63 Parts Diagrams for Muffler-Side Mount/Filter Side

Guess I bought mine just in time (from Small Engine Warehouse, and they no longer carry it either).

 

[joshlee]

Thats a bummer. Even if the the tip of the muffler is pointed toward the back? I just checked out Jack's S.E.R. and he's definitely got the stuff!

Don't do it. That is where I put my last muffler, and the exhaust fumes made it somewhat unpleasant to drive in the summer.

This time around, I installed the muffler like KMA and Kent did. Much better.

I like the idea of the heat shield. Been toying around with it for my installation, since the tub next to the muffler does get hot (and that muffler does have a heat shield on it already).

Quick cruise around the internet, and it does look like this particular version is now discontinued. Bummer.

Jack's Small Engines will sell you the exhaust header (PN 263-34101-A1) for $130, but doesn't carry the complete kit anymore.

Robin/Subaru EH63 Parts Diagrams for Muffler-Side Mount/Filter Side

Guess I bought mine just in time (from Small Engine Warehouse, and they no longer carry it either).

 

[Marks481]

Thats a bummer. Even if the the tip of the muffler is pointed toward the back? I just checked out Jack's S.E.R. and he's definitely got the stuff!

Mine was a straight tube pointed straight upward, and the fumes/heat were annoying. I am not sure if the slanted cut on the end of yours will make a difference, but I suspect it would not.

If I were you, I would mount the muffler horizontal, with the tip facing backwards. If that doesn't fit (bummer to run into things with your muffler first when backing up), than maybe you could live with it vertical. Maybe if you fit an elbow over the tip facing backwards it would improve things. The engine puts out a pretty good blast of air on the exhaust, and the elbow might help quite a bit.

 

[joshlee]

I understand. How are you making out with yours? I sure am curious to find out whats causing that problem. Is running the PTO the best test for potential overheating problems?

My only thought is to move it further back...If you park your tractor and let it heat up, you will find that the tire rubber starts to get very soft like it will catch fire eventually! Plus you want smooth curves on that new pipe, which will push the muffler either up or back anyway.

 

[Kent]

BAD GAS !!!

Even before overheating I noticed a lack of power and slightly rough running, but didn't give it much thought. Like it was running lean, which I have been told causes an engine to run hot. After the overheating incident I knew something had changed since last Fall when everything was running cool. But what?

Searching the interweb for solutions I found many, many posts by air cooled engine owners, VW bugs and motorcycle mostly, reporting overheating and vapor lock/gas boiling. Many pointed to "bad" gas, meaning gas that has too much ethanol (more than 10%), low octane, and that was blended for winter use (remember it is really cold in VT in the Winter). The gas I was running was in fact cheap gas from a mini-mart from this past Winter and of the lowest octane (89, we have three choices). How much ethanol I don't know, but I add Star Tron. We don't have any non-ethanol gas stations close by. I also noticed a bunch of crud in the clear gas filter, only imagining all the microscopic crud from a tank of that cheap gas, causing fuel starvation.

I placed an order for new fuel filters from Jacks Small Engines, though are on back order.

In the mean time I siphoned out all the gas from the tank and filled up with 91 octane from Shell.

Immediately the engine smoothed out, and had that good old powerful feeling from the Fall. I have since run the engine hard with both an acre of finish mowing and just now a half acre or so of brush mowing (tall and dead grass, small honeysuckle bushes, etc.). And son of a gun, no overheating. Plus the side fan run off a thermostat shuts off in less than 5 minutes, just like before. Before the new gas, the side fan was running for like 45 minutes.

I'll install a new fuel filter when it comes (and add it to my annual maintenance routine) and just for yucks put a fiberglass heat sleeve around the incoming gas line from the fuel pump to the throttle body to help prevent future vapor lock. Belt and suspenders.

Sad to say I have an update on overheating "solution". Two days ago it was 88 degrees (hot for VT) and I decided to try pushing the Robin by finish mowing a half acre field that had grown up to about a foot deep of thick hay grass. I went slow to not bog the engine and get a good cut, but about an hour into the job the engine shut down, overheated, and wouldn't restart until after an hour+ cool down. Interesting that the overheating was NOT due to the temperature wire/FI computer shutting down the fuel pump as before (still power to the pump and it was running), but something else, I suspect maybe vapor lock?? Lots of bubbling in the fuel filter and before shutting down the engine cuts out then surges a few times before shutting down completely.

Last Fall I cut the same field and also another half-acre field with the brush mower in one swoop also in 80 degree weather, with even taller grass, but could not push the engine to overheat. So I assumed my fix was invincible.

Oh good, another problem to solve! Or at least I can promise to be smarter by choosing the right implement for the job at hand (never finish mow tall grass) and taking a break every now and then.

The exhaust manifold bolts are tight. What else could have changed?

I am realizing that the CFMs of the fan seem about half what they were last Fall when the fan was like a tornado and kept the engine cool. I am going to take it apart today to clean/lube if possible, but if that doesn't help I will explore another fan manufacturer with a stellar reputation for long life and more waterproof (perhaps SPAL, which means I would have to change to a larger fan).

 

[joshlee]

Awesome! Thats great to hear.:thumbsup: