Case 850 (Late Non letter version) External Transmission Oil Cooler

Jon Bradtke · 2026-10-02T13:29:44.000Z

Good morning. I fired up my 850 yesterday and noticed the radiator fluid was low. I don't see any visible leaks underneath the radiator and there's no coolant mixed in with the engine oil. The transmission oil looks milky though, so I'm pretty sure the transmission plate cooler inside the radiator has failed. I had that radiator and plate cooler serviced by a local shop years ago, so it's frustrating that it's only lasted a couple of years. I'm trying to figure out why it gave up. The torque converter pressure gauge is reading 100 psi, which is way more than the 40 ±15 PSI the book says it should be. I bypassed the cooler and ran the fluid through the dipstick tube instead, and it's sitting at 60 psi. So there's definitely a restriction either in the cooler itself or in the lines. Here's what I'm actually wondering: has anyone swapped in an external oil cooler instead of using the plate cooler that sits in the bottom of the radiator? If you have, do you have any photos or suggestions on brands, sizing, and how you mounted it? I've been looking at Mishimoto Universal Oil coolers rated for 120 PSI that mount in front of the radiator. Space is really tight on the 850 with the X bracing for the front crawl gear—I've only got about 1.5" between the radiator and the bracing. Thanks for any input.

Started by Jon BradtkeOct 2, 20262 replies

Jon BradtkeNew MemberOct 2, 2026#1
Good morning.

I fired up my 850 yesterday and noticed the radiator fluid was low. I don't see any visible leaks underneath the radiator and there's no coolant mixed in with the engine oil. The transmission oil looks milky though, so I'm pretty sure the transmission plate cooler inside the radiator has failed. I had that radiator and plate cooler serviced by a local shop years ago, so it's frustrating that it's only lasted a couple of years.

I'm trying to figure out why it gave up. The torque converter pressure gauge is reading 100 psi, which is way more than the 40 ±15 PSI the book says it should be. I bypassed the cooler and ran the fluid through the dipstick tube instead, and it's sitting at 60 psi. So there's definitely a restriction either in the cooler itself or in the lines.

Here's what I'm actually wondering: has anyone swapped in an external oil cooler instead of using the plate cooler that sits in the bottom of the radiator? If you have, do you have any photos or suggestions on brands, sizing, and how you mounted it?

I've been looking at Mishimoto Universal Oil coolers rated for 120 PSI that mount in front of the radiator. Space is really tight on the 850 with the X bracing for the front crawl gear—I've only got about 1.5" between the radiator and the bracing.

Thanks for any input.
AU.CASEJunior MemberOct 3, 2026#2
Yeah, we're looking at an early machine here. I had a 750 and the exchanger in the base tank of the radiator gave out on me too. I had it brazed to keep it running, though I'm not sure if it caused problems after that. The 1150 and the 'C' series use the same setup with the cooler in the lower radiator tank. The 1150D switched to a side-mounted radiator for transmission oil, but that reduced engine cooling capacity and caused issues in warmer conditions. Before the recent 1000HR service, scale buildup made it worse and required an acid bath to clean it out. Full-width radiators like you mentioned would be the best option if you can fit one, and they're reasonably priced too.
Jon BradtkeNew MemberOct 3, 2026#3
We're talking about a late 850 dozer here, the non-letter version from around 1975. I want to keep the original radiator as is and just plug up those transmission oil cooler ports on the bottom. That way the engine radiator stays normal. I know the later models have those side-by-side radiator/oil cooler setups, but those things cost a fortune when you buy the whole package. The thing I'm stuck on is figuring out how to properly size an external oil cooler for this.

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