Temperature differences

[Mr_deco]

Hello to everyone new owner of a 1958 farmall cub. Bought it not running but now have it running. She runs beautifully. I’ve been reading about the pressurized and the non pressurized. My rad cap is missing parts. It doesn’t seal to the base of the neck only to the top. I’m treating this as no pressurized. After engine has been running for 5-10 minutes there is warm coolant coming to the top of the rad. ( normal) the return to the block has been abiant temperature with no temp change I can feel. Do these systems take a while to get moving within? I’ve let it run just a bit above idle for 20 min and the return still feels the same. If this is the normal way the system works then wow. The top on the rad is too hot to touch.

[Dale Finch]

Here is the Blue Ribbon Manual on the Cooling System. It describes how the system works, as well as servicing.
http://farmallcub.com/rudi_cub/www.cleancomputes.com/Cub/Blue%20Ribbon%20Service%20Manuals/GSS-1016%20Cooling%20System/GSS-1016%20Cooling%20System.htm

Most of the earlier cubs ARE non-pressurized systems. You may read discussions about antifreeze blowing out when the tractor heats up. They all have their own "normal" water level, and if filled too full, the excess will exit via the overflow tube.

WELCOME!!

Note: This is the type cap used for the non-pressurized system, available from TM Tractors, a forum sponsor:
http://www.tmtractor.com/new/co/1642fp.htm
Some folks who find the previous owner (PO) of their cub put a pressurized cap on, simply cut off the spring-loaded lower seal.

[Gary Dotson]

I think what you’re seeing sounds pretty normal. You’re not making a lot of heat at fast idle and the fan and radiator are cooling it back down. Put the tractor on hard labor, then see what it does. Your cap sounds correct.

[Waif]

No pump. "Thermosyphon".
Heat rises.(As heat will.) Your radiator top is evidence of where heat rises and builds in the design of the tractor.
Fan robs some heat from rising coolant.
Cooler coolant sinks. While getting fan air run through.

The expanding fluid (from heat) needs a place to go.
Your loose cap and overflow tube is where yours goes.
A snug cap would simply force the excess coolant out the overflow.

A tight/closed cooling system with no pump would be fussy trying not to damage it from pressure as heat expands fluid.
As mentioned your Cub will have a sweet spot in it's fluid level. The tendency is to run them too full.
But do be sure to have enough.
With hard work I'll usually see some coolant coughed out from where it runs (has a happy level) when not worked hard.

[Gary Dotson]

Actually a pressure cap was an option and the Cub system will work fine with one, only about 4 psi, however. A pressure cap will raise the boiling point of the coolant and may help retain the coolant level in hot, hard working conditions. My oldest Kubota mowing tractor is thermo syphon with a pressure cap. It was losing a small amount of coolant each time we mowed with it. During routine maintenance, I replaced the coolant and the rad. cap and have added no coolant in the last 3 years. Very small leak but the cap was allowing coolant to be pushed out.