I just found out that on the S/V90 (maybe previous model years) the cooling system interacts with the oil system (generally speaking) and acts as a cooling agent for the oil. I didn't know that, and I don't ever recall any postings regarding issues associated with this.
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John Shatzer, '97 V90 @ 105K

The 740/760/940 turbos came with an oil coller. Later models of the 940T had the small heat exchanger like the 960. My old 740T had an oil cooler beside the radiator.
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Warren Bain - '99 V70GLT G-Valve > 80K mi, 89 300SE, '96 965 >120Kmi, near Manassas Va.. Check the 700/900 FAQ via the 'features' pull down menu. This post written with 100% recycled electrons.

Shatz
If you had the need to replace the radiator, you would have seen the connection for the oil cooler on the left side. Keep an eye on your radiator, specially at the points where the hoses attach since the plastic gets very brittle over time and cracks. If you start to notice a loss of coolant, check this out quick.
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97 S90 with 171K miles still going strong

Exactly! I think I'm seeing early stages of this now around the upper hose @ 108K. I've had some small amounts of coolant loss recently, not enought to refill the reservoir, but enough to trip the coolant dash light. I'll order a radiator, hoses and thermostat soon.
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John Shatzer, '97 V90 @ 105K

Shatz, I just replaced the radiator last week in my V90...leaking near the hose...the radiator isn't cheap.

that means you should have coolant in AT oil..
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Gregski; european V90 '97 B6304FS2 AW3043 IGS HID

No, I don't think so. I'm speculating that there is a hairline crack in the radiator at the connection with the upper hose. It's simply seeping out of there as it expands and contracts with use. At least that's what I think the telltale residue is around that connector.
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John Shatzer, '97 V90 @ 105K

Yes, I believe it came in around '95 or '96 on the later 960s. The oil "cooler" is a water to oil heat exchanger mounted between the oil filter and the oil filter adapter. This is in lew of the external oil cooler mounted on the early 960's in front of the radiator with oil hoses to an adapter on the front of the engine. Coolant from the engine is routed to and from it by external hoses similar to the interior heater hoses.

This has the added benefit of "heating" the oil with warm coolant during the start-up phases of operation. The coolant is in the part of the system where it's temperature is regulated with the thermostat. The oil temperature is kind of held at constant temperature this way.
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'96 965 with 16' wheels at 116K. Had '85 745 Turbo Diesel for 200K.

My 94 has the water cooled oil, the heat exchanger is located just inward of the oil filter, the coolant hoses that feed it are very hard to locate, I think Volvo went through a few versions of this setup and that is why there are so many coolant hose variables.

DanR 94 964 253,000 miles (19,000 on the new engine)
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DanR

As always Jim, thanks for your lucid description! I was just a bit surprised by this feature, pointing to both the sophistication of the engine and my ignorance of it.
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John Shatzer, '97 V90 @ 105K

I think this special radiator was standard on all 960 with the inline six and auto transmission, b6304 and b6254. My 960 1991 had this radiator and so does my S90 1997.

/ Patrik, Sweden

maybe broken oil cooler above oil filter?

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Gregski; european V90 '97 B6304FS2 AW3043 IGS HID

No, I was just pointing out a design feature of the engine from a Volvo mechanic who owns a 98 S90
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John Shatzer, '97 V90 @ 105K

How does this work? Where does the interface occur?

Well, I found out about this in the context of replacing hoses, and I think my friend said that there is a coolant hose that connects to the block at or around the filter, the purpose of which is to bring coolant to the oil supply. I dunno much more than that.
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John Shatzer, '97 V90 @ 105K