Coolant reservoir full, low, then full?!

[MilehighV70XC]

Still trying to diagnose coolant loss after long drives or every couple weeks.
I pressurized the system using my Mityvac attached to the small overflow hose and reservoir nipple. Pressurized to about 21 to test cap, tested good. Bleed all the pressure off.
I pressurized the cooling system again and noticed as I add pressure above 10psi up to 19psi the level in the reservoir starts to lower. The reservoir starts at MAX and goes down to the top of the of the letters of the MIN mark. As I release the pressure the coolant goes back to the MAX mark and is full again. Coolant can not compress so where is it going?

I'm still at a loss and don't want to believe it is a small breach in the headgasket.
Compression 155,137,156,153,155
What psi does the system operate at?

Previous post- forget about the compression numbers, they where from a shop, the real ones are in the 150's
https://www.matthewsvolvosite.com/forums ... =1&t=55787

[jpr0204]

Hey there MilehighV70XC,

You are correct, you cannot compress a liquid. However, the "space" if you will, between the coolant overflow, overflow hose, and the top of the radiator itself will utilize some coolant when pressure is applied to the system.

A general rule of thumb is no more the a 20% differnece in compression readings bewtween cylinders.

I see that 4 out of 5 cylinders at just about even with Cylinder 2 being a little bit on the low side.

A 20% drop from the 150's would leave you around the 124 mark. So cylinder 2 is at around a 10% loss compared to the other ones.

This operates at a pressure of 20PSI.

What I would do for Cyl. 2 is give a squirt of oil or two down the cylinder and retest. If that 137 comes up to the 150ish range, chances are the rings are starting to wear.

As far as the small coolant leak goes, I would check any and ALL coolant hoses, especially the ones by the Turbo. I know I may be beating a dead horse here, but there are some very tiny ones that everyone neglects due to the space in which there is to change them.

- Joe

[jpr0204]

FWIW, on our 00' V70 X/C SE...

With the car cold (After sitting overnight), I keep the coolant level right the bottom of the "MAX" mark. When the car gets to operating temp., the coolant goes about an 1/8 inch above the "MAX" mark, when the cooling fan comes on, the coolant begins to drop to right to the bottom of the "MAX" mark same where it is first thing in the morning. When the cooling fan turns off, the coolant then starts to rise about an 1/8 above the "MAX" mark again.

This is all considered a normal part of how the cooling system works. Since I've put new coolant in back in 12/12 when I bought the car, I haven't had to add a drop to the system since I've had it (except when I had a small drip from the lower hose due to a loose clamp), and the level always stays at the bottom of the "MAX" mark.

[MilehighV70XC]

Thanks for the quick replies Jpr0204.
The system seems to hold pressure. I left it pressurized at 18psi and two hours later still holding. If there was even a pin hole leak wouldn't the pressure bleed off and/or lose coolant?
When I did there compression test I added some oil. I am thinking it is a valve stem seal.

I did not realize the radiator has a little air space in it. Makes sense since I have bleed the system for air numerous times. Some thing has to be compressing so that makes sense.

I understand that the level might fluctuate a tiny bit depending on temps since water does expand when hot. I would not worry if that was my problem but I am still losing coolant, diagnoses is not looking to good.

[jpr0204]

Yes, even if you had a slight leak, after 2 hours you would most definately show a drop in pressure.

I would say if the system held pressure for 2 hours with no drop, you could probably rule out the head gasket.

Headgaskets usually fail for two reasons, one main reason is... HEAT and the other is sometimes AGE...

Usually a head gasket fails if the car overheats or if the gasket begins to show age. By "age", I mean look at how many times the car has gone from cold to operating temp and back to cold since new? Each time the cold, hot, cold cycle happens that's another strike on the head gasket becuase if contracts, expands, contracts, expands...

The only time I have ever heard head gaskets going bad on these whiteblock motors is due to them running hot than they should at one point in time for some reason or another.

Now, the GM 3400 Head gaskets? Once a year... Design also plays a big part as well.

- Joe

One final test you can do to rule out the head gasket is go to Auto Zone and rent their block tester. You have buy the dye, for it but you'll get the money back for the loan-a-tool when you return it. You screw it onto the coolant tank, put in the yellow dye, and follow the instructions. If the dye turns blue in color, the tester has found combustion chamber gases entering the cooling system. If it doesn't you are good to go.

[MilehighV70XC]

No overheating problems since I have owned the car at 78k likes. Nothing in the history.
Things I have done in the past couple months
--Compression test 155, 137, 156, 153, 155- Car warmed up, all plugs out, throttle open
--The over flow bottle does have a slight exhaust smell but test show no hydrocarbons in the coolant.
--No coolant in the oil.
--No oil in the coolant
--Slight white smoke out the tailpipe when cold, goes away once warmed up, and does not smoke under boost from what I can tell
--No leaks from the heater hoses or the heater core. pressurized system at 18psi for two hours, held pressure.
--No leaks from radiator hoses
--New Nissen radiator
--New OEM thermostat

[jpr0204]

At this point, I would definately rule out the head gasket.

You seem to have covered all your bases and then some...

Not trying to be smart here, but thing I didn't see you mention was the coolant overflow tank itself.

LOTS of issues with these from very large cracks and losing a lot of coolant to very, very, tiny cracks and hardly losing any coolant but all the same, enough to show a difference in the overflow tank...

One would assume though that if the tank itself was leaking weather a large or small crack, it would definatley show in the pressure test plus you would see coolant as well. But, just wanted to mention it.

- Joe

This is definately puzzling...

BTW, how often do you have to add coolant and how much?

[MilehighV70XC]

No leaks from reservoir.
Coolant loss depends on how the car is driven. I work 8 miles form my house and don't go over 40mph. If just driving to and from work I have to fill every 6-8 days.
On longer drives the low coolant light will come on depending on how much I am boosting.
The last trip I took about 60mi one way, on the way there was boosting quite often. Light came on as I was parking. I filled the reservoir.
The way home was just cruising, very little boost, only lost maybe a 1/4in below the MAX mark.
Same thing happens when I am driving in the mountains. The amount I lose depends on the amount I am boosting. Every trip in the mountains the light comes on just lose more sometime then others.

[rspi]

Small head gasket leak. Fix it or sell it while you can.

http://atthetipwebs.com/technologyinstr ... gasket.htm

[rspi]

The thing that got me was how fast the coolant was evaporating while it was leaking. There is a chance that you have some other small coolant leak, but the raise in the bottle points me to the head gasket in these cars. Read my story on the link I provided.