Hello again'
In regard to a 1997 S90 B6230 engine, I am experiencing a mysterious coolant loss. The dash light comes on and the reservoir is down to the neck of the reservoir after less than a hundred miles of driving. There are no wet carpets or smells, no visible leaks anywhere and I have had the water pump and radiator changed about a year ago. I have read of the 960 and porous blocks, could that be the problem here?

Thanks,
Lenk

The porous blocks were only an early 1992 phenomenon, long since a problem. The most common places where coolant is lost on these (B6304) systems is :

1) a crack at the top radiator hose neck. They typically crack first then fail catastrophically. The typical life of these radiators is 10 years. Replace the radiator immediately if this is the case.

2) the coolant reservoir cap will leak coolant and leave no trace. They are inexpensive and even NAPA caries the blue cap.

3) the heater lines at the rear of the engine tend to seep where they connect to the metal lines at the firewall. You can tell if they are leaking from the staining on the metal pipes.

Check these first, if no joy, than try a simple coolant pressure test or have it tested. You don't want coolant leaking into your atf.

DEWFPO
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1998 S90 083,228 and 1995 964 154,100

There is also a plastic valve off the back off the engine that connected coolant lines to the heater core (As I recall anyway). I had the same symptoms you are describing and this was the root cause for me anyway. The part was 20-30 bucks.

Good luck!

probably this one is the cause, but I would not put a valve back on. Plug the vacuum line and put a hose directly into the heating core. The valve does nothing. you still get AC in summer.

The valve shuts off hot coolant flow to the heater core when A/C is requested. It's default (no vacuum) position is open.

DEWFPO
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1998 S90 088,900 and 1995 964 154,100

I know what the darn thing does. It has been always the culprit of coolant leaks in all my volvos. So they are gone. Not worth a engine overheat. I have not noticed any loss of AC when I need it. Just personal taste. Thanks for your input.

Pressure test is in order.
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Post Back. That's whats makes this forum work.

Thanks to everyone that responded to my post. This reply may seem negligently late and it is - partially. The one year old radiator was a cheap plastic aftermarket that was leaking. After replacement with an OEM radiator I watched the expansion tank like a hawk. To my disgust the level kept dropping. I kept refilling and searching until I recalled the post about it dropping to a certain level sent by Efrat and Carpenter. I let it drop and it stopped dropping just above the low limit mark and there it has remained ever since. Since June. I have no idea why but it works even on fairly long trips. Who would have thought the cooling system would be as abstruse as the wiring system?

Thanks again,
Len

You're losing coolant pretty fast. It "should" be fairly easy to diagnose.

Is the resevoir cap good and tight - any stains on the outside of the resevoir?

How does the tranny fluid look? (New radiators can fail internally just like an old one.)

How doeas the engine oil look? Creamy or foamy at all? Could be bad a head gasket or porous block weeping into the crankcase.

Look all over the outside of the block for stains from porous block or maybe a freeze plug leaking.

Is the inside of the windshield getting oily from the defroster?

Any dripping under the car after you park?

If you remove the coolant cap while the engine is idling do you see any bubbles coming up through the coolant?

I had a 95 960 losing coolant about that quickly with no obvious traces (oil was clean, radiator fine, new hoses, etc.) so I replaced the resevoir cap. No change. I noticed it would get down to the resevoir neck quickly but the level dropped very slowly from there.

One day I happened to see some moisture around the seam where the top and bottom halves of the resevoir come together, and suddenly it became obvious. Ordered a new coolant expansion tank from FCP and cured the problem.

Same for me, the fluid level would never go below the reservoir.

Just last week a friends 960 started losing coolant with no perceptible evidence of were it was going. Turned out to be a pressed in casting plug on the water pump he replaced 1 year ago was faulty and leaking.