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

[MuncyBob]

It seems to me, since your muffler is outside of the engine compartment, that wrapping it would have little benefit.

Probably so, but it would look "cool" A possible reason to do this though is because the muffler gets up to/over 600* and is only inches away from the fuel pump.

I'm also thinking about modifying the heat shield between the gas tank and the manifold. It seems to me that the shield's shape keeps more heat trapped under it than if it just went straight up?

 

[cqaigy2]

Probably so, but it would look "cool" A possible reason to do this though is because the muffler gets up to/over 600* and is only inches away from the fuel pump.

I'm also thinking about modifying the heat shield between the gas tank and the manifold. It seems to me that the shield's shape keeps more heat trapped under it than if it just went straight up?

Well sure the "coolness" factor.
Maybe extend the muffler heat shield up a little higher on the engine side.
That's a good point about the heat shield, i wonder if it would radiate more IR into the oil cooler?

 

[Marks481]

A possible reason to do this though is because the muffler gets up to/over 600* and is only inches away from the fuel pump.

Better solution: move your fuel pump. Mine is mounted underneath the fuel tank bracket on the right hand side, and the fuel hose is routed underneath the air filter housing to the right side of the engine compartment. The fuel pump is pulse driven by crankcase pressure/vacuum... all you need is an extra length of vacuum hose to move the fuel pump anywhere you want. Getting the fuel hoses as far away from exhaust tubing and away from contact with any hydraulic components was a high priority.

The first place I relocated it was bolted to the underside of the left gas tank bracket. Bad choice as all the hydraulic blocks and hoses near there did a good job of cooking the fuel pump 9not as good as the exhaust, but 200F+ solenoid blocks is a bit more than you want).

Oh, and you are better off mounting a thin metal plate between the exhaust and the engine compartment hood. That will do a better job of preventing heat intrusion than wrapping your muffler.

 

[MuncyBob]

Moving the fuel pump is probably a good idea. Now that I have wrapped the exhaust to the muffler I'm finding that I am getting backfire at shut down...even if it is on low idle for 30sec to a minute.

 

[jfischer]

Just my two cents here, but I tried the wrap on the stock header and found it made the heat stay in it, and made things hotter to a point, and I know the stock muffler wrapped was up to 800-900 degrees with it wrapped after working hard. It backfired, or would do the diesel effect after I idled it all the way down for a minute or more.
I put the stock Subaru header on it, and made all up to use the stock Subaru muffler with making the flanges so they didn't have a lot of bends, straight into the muffler, and made brackets up so it is solid as the engine is, and have had good luck, temps and all with it.
I also have a 10" fan on the opposite side which I think helps also.
I am at about 65 hours with the machine now, and have really had NO problems with the engine. Changed it over to Mobile 1 at around the 20 hour mark, and seems to run as well as can be expected.
After doing, and trying the wrap, I think it just holds the heat in more. Getting the header up 2-3" higher, so the air can flow more seemed to help, and it is even a bit quieter then before.
If you look back a few posts in this thread, think it was #8 or so, I put some pictures of what I did that seemed to help. I think the machine could still use more power at low end, would be neat to find a nice small diesel, think they had a 430 at one time that had one in it, and was a 425 size machine. Guess it didn't last, or was too expensive to put the engine in it.

 

[cqaigy2]

Im not sure i understand when you say it 'holds the heat in more'? Do you mean that the ambient in the engine compartment is hotter with the wrap?

 

[jfischer]

It seems to hold the heat in the metal, and makes it hotter. Kind of like a head on an engine without any fins for the air to cool it down. The wrap seemed to hold the heat in the exhaust header, and with it making a smaller place for the cool air (or the fan in the engine to blow air out of the engine compartment) didn't help as much as I thought it would.
Wrap is mainly used on motorcycles, race cars and such to keep the heat from getting from the object that it is wrapped on to getting to the floor board of cars, or the riders legs on a bike. I think it is also used in some cases to keep the engine in the heat more in some applications. That on my square exhaust that PT uses made it hold the heat in the metal, and the fan could not blow it away, or across it as easy as being unwrapped.
Might have been just how it was with my machine, but I took the total exhaust off, and made all new the way I felt PT should have done and not tried to cut corners with what they put on it.

Im not sure i understand when you say it 'holds the heat in more'? Do you mean that the ambient in the engine compartment is hotter with the wrap?

 

[woodlandfarms]

Mileage varies on this, but honestly from what I studied when working on old cars, if you can get a ceramic coat on the INSIDE of the exhaust, it massively reduces heat in the engine compartment. I was able to put my hand on my headers after driving around on a normal day and not get burnt (it was hot, trust me) Opinions on wrap in the auto world are that it is very old technology. metal gets hot still, and the wrap just gets hot as well.

 

[ponytug]

I agree with Carl. Ceramic coatings on the inside are really helpful for moving heat down the tube, which is helpful in modified older cars and goosed up turbo charged cars. I think of the heat in the exhaust gases as a gradient. If you put the insulator inside the exhaust header, most of the heat gradient is inside, so not much is available at the metal header surface, so not much radiates out. But the heat is still there, you have just moved the heat farther down stream, rather like kicking the can down the road. Whether you want the heat farther down the exhaust system is another question.

That said, I think that jfischer's solution of a modified stock exhaust with a fan may be more...doable.

On the PT, I wonder if ceramic coating a square header isn't a bit like lipstick on a pig, because the stock system seems to have issues. Icing on the cake might be coating the Subaru stock header, but, and it is a hypothetical but, I worry about having a higher temperature exhaust. At least some of us are worried about igniting things like dry grass with our tractors.

As always, YMMV...

All the best,

Peter

 

[MuncyBob]

Bringing this thread back to life for a moment....grass cutting season is here again so I finally got around to ordering the Subaru muffler kit and it should be here around the weekend. Exactly how do you ceramic coat the inside of the header? Would a body shop know what I'm talking about(because I don't!)?