which radiator cap is correct for my ym240?

[bassfishrman]

I need to replace my radiator cap and don't know which psi cap is correct. My shop/repair manuals haven't arrived yet for reference. Can anyone help?

Thanks from a new yanmar owner!

 

[SailorBob]

I bought a radiator cap for a 72 Datsun B1700 on advice I found in another post on this forum for my YM1700. It is a 13 pound and fits like a glove. I am not 100% sure it is the same for yours. Maybe some of the senior members will know for sure.

 

[normde2001]

Apparently, it depends on who you talk to. My YM2000B has a 13#; however, when I ordered a spare from Hoye, they sent me a 7#. I asked Aaron if that was correct, he said that was what the cap manufacturer recommended for Yanmar's specs, but either would work fine. Are there any cooling system gurus out there that know what the dif in operating temp might be between the 2? My 2000 barely gets off cold with a 13# cap and I don't have access to the tractor for now to try the new one.

 

[SailorBob]

Norm,

You may be right. The 1700 has does not have a water pump but, I believe the 2000 and 240 do. The main reason that I replaced mine is because the radiator was pumping fluid into the overfow bottle while in use. It has stopped that since I installed the new cap. I think that the thermosyphon models may need more pressure to force the water to circulate properly.

 

[California]

Per the I&T Shop Manual, generally considered an excellent source:

"The cooling system operating presure should be approximately 12.8 psi and is maintained by the radiator cap."

My YM240 (US version YM2000) had a 7 lb cap. The first time I got the radiator fins cloggged with mowing chaff, it boiled over before the warning light came on.

I bought a new cap at the next available presure above 12.8 psi which turned out to be the 14 lb cap from 70's Datsun. Now the warning light glows before the coolant boils.

I figured this all out at the time, but from memory I think a 33% mix of coolant at 14 psi boils at 255 degrees while the Yanmar warning light comes on at 238 degrees.

Also, it is important to find a cap with a return valve in the center. As the engine cools, coolant must return from the overflow reservoir back to the radiator.

 

[1danny]

The correct radiator cap is 13#, the temp light should come on at 212 degrees + or - 5.4 degrees. The light should go off at 197.6 degrees + or - 5.4 degrees. I have the caps & manuals in stock if you need them.
Danny