Added an extra cooling Fan

[kludge]

I wanted to share a modification that I have made to my PT425. The initial reason I had for adding an extra cooling fan is an unseated valve and bent push rods. The earlier PT425's have the front of the Kohler engine down in the box at the front. This location on mine wasn't able to pull enough fresh air through the engine. The side benefit that I have enjoyed has been the icing on the cake for this mod. With the extra fan blowing down into the box, the positive air pressure keeps the grass clippings from being sucked into the engine box area. I haven't had to clean the front of the engine off after mowing.

Now for the details. First I ordered another fan. I went ahead and used the same SPAL fan that is on the oil cooler. It draws around 6 amps. I had some concern about the alternator being a 15 amp source. After talking to the small engine shop whom I had replace the valve seat. They were of the opinion that the alternators almost always supply more current than advertised.

Next I had to build a box to mount the fan in. There was not enough space to mount the fan flat. I cut a 6" x 11" hole in the top of the engine compartment cover. Mounted the fan and box upright on top of the cutout.

I tapped the wires for the oil cooler fan before the temperature switch.

Finally I used flashing to close off the front of the engine compartment cover and 10" back on each side. Under the cover I added a flashing panel extending from the top down to the top of the air filter cover. This had the effect of channeling the air from the fan down to the front of the engine. Activating the fan I could feel airflow coming out the back of the PT425 near the bottom

The one drawback that I have run into so far is that when the oil is hot and both fans are running, there is barely enough amperage to crank the engine. I haven't decided whether to change the battery to one with a larger cold crank capacity or simply add a normally closed pushbutton switch to the circuit to act as a temporary fan kill switch for cranking.

 

[kludge]

Hopefully this post will show a pic under the cover.

 

[BobRip]

The one drawback that I have run into so far is that when the oil is hot and both fans are running, there is barely enough amperage to crank the engine. I haven't decided whether to change the battery to one with a larger cold crank capacity or simply add a normally closed pushbutton switch to the circuit to act as a temporary fan kill switch for cranking.


Nice looking modification.
I am concerned that you are discharging the battery while running both fans. The alternator output is only 15 amps if the engine is running at full speed (3600 RPM). While cranking an additional load of 12 amps does not seem like much unless the starter is not getting enough voltage to engage, the push button seems like a good idea, a relay that is engaged with the starter and opens the fan power would be automatic. Does it crank slow or just not engage the starter. If you have a multimeter check the battery voltage with both fans running and the engine at full speed. You must have at least 12.6 volts to keep from running the battery down, and 14 volts would be much better. A larger battery will not help for long if it is being discharged while using the tractor. Still with a larger battery, you could trickle charge the battery between uses and probably get by. Better to run a battery down than overheat an engine.

Bob Rip

 

[kludge]

I am one of those operators that runs the engine at full throttle whenever I am using the PT. I have put 20 hours on since the modification and haven't run the battery down yet. The sympton with a warm engine is the dreaded click - click then the engine starts turning over. This occurred the first day with the modification. When first starting the fans actually draw more than 6 amps until the fans are turning. I like the relay off the starter idea. This seems to be the slickest solution. The trickle charger was my backup plan. /forums/images/graemlins/smile.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/ooo.gif

 

[cqaigy]

Nice looking mod!

 

[Marks481]

where did you order the SPAL fan from?

I have been thinking that maybe another fan mounted on the right hand side of the canopy, so that it blows across the exhaust manifold might be worthwhile. It would circulate air acros what is probably the hottest spot in the engine compartment.

 

[BobRip]

If you turned the key to on and let the fans get upto speed the current would drop and then it might start better. This is all a little too marginal for me, the relay solves it all.

Thanks for this concept and pictures.

Bob Rip

 

[J_J]

A good volt meter will help solve some of your problems. Hook it up to the battery and turn switch to on, observe the voltage. Turn the key to start position, and observe the voltage. With engine running, you should see the charging voltage.

You could also add another battery to the circuit, with a one way diode so that the fans run only off the second battery. The engine would charge the second battery, but it would only be used for the fans.


There might also be a larger alternator for that engine.

 

[kludge]

<font color="red"> </font> where did you order the SPAL fan from?

<font color="black"> </font> The fan is a SPAL VA11-AP8/C-29A. Ordered cost $62.00 + shipping. This is the pull version. Hindsight says that I should have used a push version. You want to find a Hot Rod shop close to reduce the shipping.

 

[J_J]

You should be able to reverse the wires to make it run the other way.