IH 1066 coolant problem

I have a 1066 with a 466 engine in it. I have been using it on my tiller lately and it has been do great. The problem is that when its warmed up if its been running at pto speed and I idle it down to turn around, it spit coolant out of the overfill. it will do that for a couple of seconds and then stop. if I idle it back up it will stop coming out sooner. I have taken the cap off after it has done that and there is white foam close to the top of the radiator. I keep the water level just above the fins. does anybody know why it does this?

you have compression entering the coolant. could be bad head gasket or crack in head, maybe pitted liners.

that was my first thought but why would it only do it when I idle down? seem like if it was a leak it would be worse at a high idle.

Do you ever check the coolant for SCA's if not then it is probably a liner hole. There are kits for checking. I check the tractors all once per year. With the number ad amount of use most never see 100 hours per year.

Have you had this tractor long and has it done this before. Or , have you changed radiator.

Reason for asking. We had a lot of problems with those tractors when new. For no good reason they would do just that, spew coolant when throttling down from a load.

IH's cure was to change the baffle in the radiator. The field fix IH supported was adding a coolant recovery tank in front of the pre cleaner baffle behind front grill. That and a radiator cap for recovery systems. Installed quite a few of them back in the 70'ss.

A little story behind this. Boss gets in a customers tractor , has a new radiator on hand because customer says radiator is leaking. I put new radiator on. Same problem.

Thing is no one discussed problem with me, just put on new radiator. About that time IH started getting numerous complaints and got to the bottom of the problem.

The original over flow hose was so short that any amount that came out of the over flow was picked up by the fan and it ended up on lower corner of radiator.

New baffled radiator and longer overflow hose came on the newer tractors.
Now, not saying this is your problem, just a possibility. Also, some anti freeze will foam some normally. Not all but some.
Next, if I really suspect combustion leakage, I fill radiator to the point of over flowing. Remove belt from water pump, and with cold or cool engine, start engine, rev engine up and down to high rpms a few times and watch for a rise of the coolant. NOT bubbles as they may be in rear of engine and take a while to surface. This is a 30 second to a minute test because the normal heating of engine will make it rise, BUT, if it raises up and out right away, you have a combustion leak. Head gasket, head or pin hole in sleeve.

First I am in uk.... in 1978 I remember driving a new 946 back from a show at Welshpool to depot at Newtown, when I shut it down coolant came over the top but it went to another dealer so I never knew what happened to it
I have just thought of something... is radiator core clean and I don't just mean not blocked as a coating of dust will act as insulation also is fan blade clean?

my 660 does the same thing and i know its the head gasket. i need to keep it idled up at 1200 rpm or it will puke out the coolant plus can see the small bubbles in rad. it the opposite at idle it will flow out the coolant thats why need to keep the running fast. thats my experience.

I have not had it very long and it has done this every since I got it. thinks for the suggestion.

Does the engine come up to operating temp relatively quick, especially if there is not much load on it? I am asking this because I am wondering if there is a thermostat in it. Without one the coolant may circulate to fast and foam up. Not sure if that has any explanation as to why it overflows coolant. Easy way to check for a thermostat is to open the cap right after you start it cold. If you see circulation right away it does not have a thermostat or the one in it is stuck open. This is one time I would also recommend going the easy fix first, by trying a new cap. After checking out these items if it does not use more than a quart or two in 3 - 4 days use I would run it. The other posters pointing towards compression coming into the system have valid points. There is the possibility of a failure that would fill the cylinder with coolant and hydro-lock a cylinder. Probably a good idea to crank this engine a couple turns with the throttle in the stop position first. Then give it fuel on the second spin once you know no water is leaking any cylinders. On a side note, I had no idea what a 946 was as stated by the poster from across the pond. I figured that he was likely talking about some other foreign brand. Turns out it could possibly be an overseas IH model, see link.
IH 946

if you suspect combustion leaking into the system there is a test fluid than can be added to the coolant that will detect that but its most likely what pete 23 described .