Checked fluids on my '96 965 and noticed the coolant was brown and had unusual smell. I flushed cooling system last October at 142K miles and refilled with Volvo coolant and distilled water. Since then I've driven about 5K miles. Two months ago, I replaced the gaskets on the oil cooler, which required draining much of the cooling system again. The coolant, which I reused, looked very clean at that time. Other vital signs:
* No overheating & engine runs smoothly.
* The motor oil shows no signs of water contamination.
* The ATF, which has never been changed, looks like what people on the Board say their original fluid appears when they drain it. (I was just getting ready to change it when this issue appeared.)
* The radiator in this car is 7 years / 40K miles old.
* The coolant side of the oil cooler showed no obvious signs of damage - I worked on it to correct an oil leak.

Guess it could be the oil cooler, the radiator, or ?? Looking for suggestions on how to trouble-shoot this.
Thanks.
96 Volvo 965
71 Triumph TR6

Here's a postscript on my brown coolant issue. Turned out it was ATF in the coolant - entering via failed trans cooler in the radiator. I was just about to replace the engine in this car - thinking it was oil in the coolant - when the transmission started acting like it was low on fluid. And it was! Tech confirmed broken radiator by connecting shop air hose to trans coolant line and watching for bubbles in the coolant. So, new radiator, multiple coolant and ATF flushes and car is good so far. I'm hoping any coolant that got into ATF lines didn't damage the transmission. The advice in the thread re. having a lab analyze the fluid to find out exactly what's contaminating it is on the money.

Also, the S90 parts car I acquired for a replacement engine is now for sale if anyone is interested.

Possibly a change in coolant chemistry caused one or more additives to change or be consumed and rust protection -ran out- and thereafter rust built up.

Did you run the heater when you did the flushed? Perhaps the heater core could have retained some old chemistry.

The trucking industry has had a lot of issues with mixing coolant chemistries out on the road. Some combinations can really mess up a cooling system.

While not cheap, I would do another flush, making sure to come up to temp and run the heater each iteration, and to fill with Volvo antifreeze recommended for your car.

My 2008 XC70 does not use the same coolant as our 850s did.

Instead of guessing, you can always send a sample of the coolant out for analysis. Here is an example of one lab that offers this service: https://polarislabs.com/coolant-testing-and-analysis/

I don't have any experience with them- a search will show a number of testing lab options.

I have had oil analyzed in the past. Big trucks with huge sumps change their oil based upon testing results to get the most values out of an oil change, but the results can zero in on head gasket leaks and bearing failures by metals showing up in the oil. A coolant test will tell you exactly what is happening. In my opinion a color change in ANY engine is not a good sign.

Dear analogdad,

Hope you're well. If the oil cooler is in good order, I concur in view that the coolant/water ratio was wrong.

The in-radiator automatic transmission fluid (ATF) cooler is unlikely to have failed. It consists of a heavy-duty, double-wall copper tube. For this unit to fail, it would have to pin-hole. That's possible, if the coolant was seriously neglected for years. If so, you'd see a pinkish scum atop the water in the coolant overflow tank. Also, the ATF would be milky/cloudy, rather than a clear, rosy red.

Hope this helps.

Yours faithfully,

Spook

Spook,
Good to hear from you on this one. I agree that the contamination looks more like oil than trans fluid.

I'm the second owner of the car. Carfax shows PO serviced car exclusively at Volvo dealers. Coolant ran clean for 1 year after I changed it last October - so why would rust suddenly appear now? Also, as I bet you already know, the I-6 in 960 cars is all aluminum - so what's the source of rust?

BTW, there are some good threads here on how oil can contaminate the coolant w/o coolant getting in the oil. They point to a bad head gasket or (sob) cracked head.
John

Dear analogdad,

Hope you're well. A coolant pipe (Part #9142746) brings hot coolant from the radiator to the heater core. I'd guess that pipe is steel. If so, an improper coolant/water mixture could allow the pipe to corrode. Further, I do not know whether water pump impellers on 960 pumps are steel or brass. If steel impellers are used, those, too, could corrode.

This said, I'd guess the source of the brownish discoloration is oil, not rust.

Hope this helps.

Yours faithfully,

Spook

Thanks Spook. I'd love the problem to be a rusty, external pipe. I'll have a look and let you know. Also going to look more closely for oil residue inside the plastic reservoir & cap.

Spook answered the past question. Metal tubes and water pump impeller. Could also be the type of antifreeze that was used. Could have been the Orange color type and it's real old. My wifes PT Cruiser Uses the new Orange Type.

Thanks. I'd love the problem to be a rusty, external pipe. I'll have a look and let you know. Also going to look more closely for oil residue inside the plastic reservoir & cap. BTW, per advice on this board, I used green coolant purchased from Volvo dealer.
John

Just guessing if you're not the original buyer. I would suspect someone ran just tap water with coolant. Instead of distilled.
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Post Back. That's whats makes this forum work.

Aleekat,
Thanks for your advice. I'm the second owner of the car. Carfax shows PO serviced car exclusively at Volvo dealers. Coolant ran clean for 1 year after I changed it last October - so why would rust show up now? Also, the I-6 in 960 cars is all aluminum (block and head) - so what's producing rust?
John

Someone didn't keep up with the mixture of coolant. The brown is from the engine. Rust due to weak mixture and tap water.

Nathan,
Thanks for your advice. I'm the second owner of the car. Carfax shows PO serviced car exclusively at Volvo dealers. Coolant ran clean for 1 year after I changed it last October - so why would rust show up now? Also, the I-6 in 960 cars is all aluminum (block and head) - so what's producing rust?
John