So heres a weird issue with my 94 850 turbo.

Last week we went on a vacation to the Jersey Shore (600 mile round trip from CT)

Before going I had to fix the A/C clutch, replace oil cooler hoses and do a tune up and oil change.

So I decided to do a complete "seafoam" treatment and flushed the coolant. Just prior to this all I had needed to add a little coolant to the tank once in a while. (would be at "min" and need to add like a quart of water to get it to "max") had to do this about once every two weeks or so.

After flushing and refilling I noticed a small crack in the cap. Nothing major and NO problems with temp so I didn't replace the cap. Didn't lose ANY coolant on the trip (even though we drove around for a week in 100 degree heat the gauge stayed right in the middle and there was NO lost coolant.

Today on a 20 minute drive the Low Coolant Level light came on. I got home and raised the hood and the cap (the better Green one and the 3rd in 4 years) had EXPLODED! I mean this thing is all apart.

So here is my question,

Low Coolant level / broken cap...which one is the cause and which one is the symptom?

Did the cracked cap breaking cause the low level or do you think there is maybe a bad head gasket burning up coolant and increasing temp/pressure and that broke the cap?

NO OIL in Coolant and NO COOLANT in the oil. No funny smoke or "hot car/anti-freeze" smell. Even with the light coming on I got no rise in the gauge above normal.

Suggestions?

 

You should not have to add fluid. The fact that you are having to do this shows you that you do have a leak...somewhere.

Because of your story i am going with a blown head gasket. Most people think if they have a blown head gasket that they are going to lose fluid and that is expected as the pistons create a vacuum the coolant is sucked into the cylinder. Small amounts may not show out the tailpipe.

There is an opposite to this. Each compression stroke will force air through the rupture into the coolant system, turbo cars being even worse. This pressure can build and swell your expansion tank. On a bad rupture you can actually see/hear the air bubbles making their way through your system.

This is just a suspicion, you should get a leakdown test done and have your coolant system pressure tested.

 

I bow to Boxpin's knowledge (and always will!), but if the cap exploded wouldn't that drop the boiling point of the coolant and cause evaporation? Maybe the crack has existed for some time causing the boil-off and it finally hit the wall and fell apart?

Why have you had so many caps? Problems or preventative maintenance?

 

+1

I am thinking that the cap was bad and only got worse over time. Then, it finally broke and all the coolant boiled out of the expansion tank. I would replace the cap and refill the system, then go from there.

 

If the cap goes the coolant leaves, thats how I lost my first engine.

 

Here's the logical way to look at this: Which is cheaper, a head gasket replacement, or a new coolant resivoir cap? if you arent gonna go through diagnosing, replace what's cheap first. In this case, it's obviously gonna be the cap. You have to get a new one anyway. Also, if it's the head gasket, replacing the cap isnt gonna do any more damage than you already have. Also, once you get a new cap and get it refilled with coolant, you can THEN do a leakdown test and see what's going on. You may have a blown head gasket, or it might just be the cap. if it's just the cap, celebrate with a beer and a burger and keep on driving. (after you sober up from the beer, that is)

 

forgot to post a resolution a while back, your post reminded me, I replaced the cap and topped up the coolant. A week later on a rather hot day i noticed the level light came on for low coolant. I got nervous thinking OOPS the new motor may have to be sped up to completion! Well, then I thought about what was going on and I realized that I had flushed the coolant just before going on the trip and like a dope I forgot about draining the coolant (with flush) from the block. (Only did the radiator) so I am thinking what happened was the stuff in the flush which must have lowered the boiling point was over pressurizing the system. The cap (the faithful VOLVO part that it is) held out for me to finish my trip. The crack then allowed the boiling over, I drained the coolant and rinsed with water then refilled and put on the new cap and OUILA! all is well.

 

Which cap is best? The grey or the green one? They both have 150 kPa stamped on them.

 

Green