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Farmall 400 radiator cap


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Having a hard time finding a radiator cap to fit Dad's Farmall 400. Bought the one that said "Fits a whole buncha IH's including the 400" at the farm & fleet store, and it's way too small.

Steiner gives two different "inside" measurements for caps, one is 2.050" and the other is 1.5". Doesn't say WHERE to measure, though... This one is "none of the above" by my interpretation of "inside." The inside measurement for the neck is closer to 2.5", it's almost 2.75" to the outside of the neck.

What cap do I need?

The cap must've been bad for years, because the tractor was down over 2 gallons of coolant. Never got hot, but the last time I ran it, it got unusually warm for just sitting idling... When I opened the radiator, the cap came off in pieces. The coolant was just evaporating out little by little every time Dad spread a load of manure with it.

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19 minutes ago, Nebraska1206 said:

163361 is the current p/n from CaseIH for this cap.  Only one listed in the partsbook.

Yeah but is it the "right" one? I don't want to be ordering cap after cap after cap and have them not fit, not fit, not fit.

Further digging, Steiner has no fewer than THREE different-sized caps listed for the 400, and none of the measurements make sense.

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55 minutes ago, Matt Kirsch said:

Yeah but is it the "right" one? I don't want to be ordering cap after cap after cap and have them not fit, not fit, not fit.

Further digging, Steiner has no fewer than THREE different-sized caps listed for the 400, and none of the measurements make sense.

Same cap I've sold for over 20 years for that application with no issues.

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Not sure if used on tractors when built but have run across ones with a small neck that used a cap like GM did in the sixties and probably longer. If I remember some had a large diameter hand grip on top of small cap.

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i looked at the cap on my 400 yesterday  and nothing odd about it. i even took the 560 cap and tryed it and it fits. the only diff is the 560 has the fancy top on the cap.  if you want me to measure it up i can. my 400 is a none touched original unit.  

IMG_5675.JPG

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27 minutes ago, Jeff-C-IL said:

A old rebuilt radiator could have a odd size cap - some local shops would do random stuff.

yes, on my 450 the rad shop put on a new neck and it takes the regular auto cap. but this 400 is original.

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On 2/2/2024 at 1:03 PM, HydroTek said:

amazon has one for 22 bucks

inside of the neck should be 2 inches

What's considered "inside?" The inside of this radiator neck (first steap) is 2-1/2", but the inside inside (hole that actually goes into the tank) is about 1-1/2".

None of the measurements match up with anything I've found. 

The cap from the CaseIH dealer doesn't fit. It's too small, same as the one I bought off the rack at the farm fleet. The one CaseIH sells is a standard automotive cap.

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That's the 'big cap' -- the spring foot is the measurement -- it has some clearance to the inside of the neck -- but the seal sits on the top of the hole, if that make sense

IH only used 2 sizes of pressure radiator caps -- the tops were different shaped  depending on the tractor , but the lower parts were only 2 sizes

Your tractor should have had the cap with the 'handle' on it originally

others were round , or had 4 'ears'

The small neck would have only 2 'ears -- and may have the large rubber cover (which could be removed)
...or the metal top with 4 'ears'

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6 hours ago, Matt Kirsch said:

What's considered "inside?" The inside of this radiator neck (first steap) is 2-1/2", but the inside inside (hole that actually goes into the tank) is about 1-1/2".

None of the measurements match up with anything I've found. 

The cap from the CaseIH dealer doesn't fit. It's too small, same as the one I bought off the rack at the farm fleet. The one CaseIH sells is a standard automotive cap.

Measured  2-1/8 ID and 2-3/4 OD so the standard cap probably fits. One rusted pictured mounted with two ears on the 400 was standard one used, others would fit. Like Hydrotek posted if the OD fits the rubber contacts the step, long as that seals and releases pressure at correct setting a standard type cap should work. Does on radiator I measured.

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  • 2 months later...

Well, exactly what I didn't want to have happen, happened... I am now the proud owner of a collection of brand new non-fitting radiator caps that will cost more to return than I paid for them.

The last one, a Gates 31324, I've been waiting for since April 3rd. It was supposed to be delivered on Eclipse Day but apparently the eclipse screwed up the mailing systems and it didn't show up until today. That one is WAY too small.

Now for the really maddening part. The first cap I bought from the farm fleet store now FITS??? I tried several times and spent no less than a half hour wiggling and jiggling and trying to force it on back in February. It just wouldn't go over the neck of the radiator. The cap was barely, but obviously too small. Today I got it out to compare to the original again, and just for giggles, tried it. Slipped right on. I don't get it.

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I am only aware of 3 sizes (diameter) of cap on tractors

Standard (medium) , Large (older tractors) , Small (compact tractors)

There were a couple of different length -- for the depth of the filler neck to the sealing step

Are the "ears" on the neck straight on the sides ?

and the filler neck is round ? -- not distorted

Your 400 should have the large size pressure cap

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20240418_131106.thumb.jpg.ab8baa4d41230cd24ea339b671c0e727.jpg

54 minutes ago, HydroTek said:

Your 400 should have the large size pressure cap

Understood, but what is "large?" I've measured the cap and neck six ways from Sunday and none of the measurements I came up with jive with any of the measurements that are advertised. That's how I ended up with a pile of radiator caps.

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2 hours ago, Matt Kirsch said:

Got one of those from the local CaseIH dealer. Doesn't fit. Too small.

Is a used one out of the question?

Mike

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2 hours ago, snoshoe said:

In case you missed it. First one he bought fits.

Yup. The first one wouldn't fit when I bought it. It was clearly too small. Not by much, but it was too small. Wiggled. Jiggled. Shoved. Turned it 1/2 turn. Wiggled. Jiggled. Shoved again. No-go.

Yesterday, I tried it again, and it fit. Just barely, but it fit.

Then later in the day I wasted $40 on tire tubes to put a worthless tire on a $5 rim... So it wasn't my day.

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