tips to find a very slow coolant leak with no visible signs of leakage? 1/4" down over 10 days time

is there method (pressurization maybe) of motivating the leak to show itself?

The method cited in the Volvo is a kind of leakdown test, and is very helpful in finding leaks.

Basically, it uses a cap to the overflow reservoir that has a hose coming out of it with a pressure gauge and a stopcock (ball valve or other type of valve), and a fitting to apply pressure with a pump.

I'm sure it costs a lot to buy, but it is possible to make one. I did this using an old radiator cap, some 1/4" plastic hose, a pressure gauge & ball valve and some compression fittings.

I use a bicycle pump to pressurize the system to ~23psi for the 150 kPa 960 system, then close the stopcock and observe the leakdown.

If you observe leakdown, then you try to find the leaks. With the car cold, it's a lot easier to identify these. You fix all the ones you find and not the effect on leakdown. There will always be some leakdown. If you can get it down to a couple of psi in the span of a few minutes, then you're doing pretty good.

It helps to do this when it's nice and quiet as you must listen for any leaks, like at the cap itself. Since there's not much air in the system, it doesn't take much volume escaping to lower the pressure a couple of psi.

Once you've fixed all of the visible leaks you can find, if you've still got coolant loss, then you start looking into the possibility of head gasket seepage. This is done with a chemical test for the presence of exhaust gases in the coolant system. This is also a very sensitive test; very small amounts of reducing exhaust gases will cause a color change in the chemical indicator. So much so that 'false' or questionable positives are often a concern.

As head gasket seepage gets worse, it will usually cause some misfiring in the morning on cold starts as coolant will have seeped into one or more cylinders overnight and will cause misfiring and uneven running for a short duration immediately after starting. One usually waits until this happens before they start thinking about taking the head off.

In your case, if there was still coolant loss after fixing all the visible leaks, I would think about using some BarsLeaks in the system before I would even think about taking the head off. I've used the dark liquid orignal BarsLeaks in various Mercedes & Volvo engines without problems. It can be quite effective on small leaks like you describe.

It is best though to start with troubleshooting/fixing all the visible leaks first. These will be all the hose interfaces and fittings around the motor; top, sides, back & bottom.

a few years ago i built a pressure bleeder for brake bleeding out of garden insecticide sprayer with a an accurate in 1 pound increments pressure gauge added tot he sprayer. to do the brake bleeding i got an extra master cylinder resovoir cap and added a brass fitting my air hose would attach to. the whole thing worked GREAT.

i di not have a coolant pressure tester and did not want to go the stant route as i am a cheap yankee and like to invent or build my own stuff where possible.

so i started messing around with an extra coolant tank cap to repeat my brake success. while i was going through all the nonsense motions of feeling really clever my 6 year old grandson intently watch grandpa doing all this picked up the brake cap with the hose attached and picked up the coolant cap with a new brass fitting in it and said:

grandpa these are the same!!!!!

i stopped and picked them both up and looked stupid. indeed the brake resovoir cap FITS PERFECTLY onto the coolant tank. and works actually much better than the radiator cap.

anyway to make a long story shorter pressure testing at the tank shows a small pressure loss. carefully removing the heater core hoses and reverse pressure testing the system sans heater core reveals no pressure loss. hooking up the pressure tester to a 1/2" plastic tee pipe with one short hose on each end of the tee and connected to each of the 2 heater pipe in the firewall reveal THIS is the source of the pressure loss . the upright part of the tee has a brass fitting into that has been clamp in the tee with a PEX pipe tool crimper and stainless steel 1/2" clamp.

YUCK, a heater core!!!

moral of the story.........anytime i have a problem to solve and want to do it more efficiently i will consult my grandson.

After reading your post I walked down and took a look at the caps. A casual glance would seem to indicate the radiator cap is bigger, but an actual swapping out proved they were if fact the same size and thread.

That is great to know as I already use a brake cap with a schrader valve in it to pressure bleed my brakes as well as pressurize my turbo plumbing to check for bad hoses.

In reference to pressure testing a cooling system; I wonder how I can incorporate a pressure gauge in a simple setup like that?

Randy

here are the pictures of my setup.

the tee is great for testing the heater core or coolant system WITH the proper radiator cap attached

http://www.brickboard.com/GALLERY/images/7696.jpg

http://www.brickboard.com/GALLERY/images/7695.jpg

http://www.brickboard.com/GALLERY/images/7694.jpg

I wonder how I can incorporate a pressure gauge in a simple setup like that?

I reckon the easiest way would be to cut the supply line, insert a barbed tee. Use clamps so your test setup does not leak. For the gauge, a cheap tire gauge with the longest hose you can find from the auto parts store would work. Cut the end off and clamp it to the tee. Plastic tees can be found in the Motor Mite HELP! section.
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Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 52 year old fat man.

It is too late to edit my post. After I posted that I was dinging around with Google and I found a gauge.

http://www.getagauge.com/

The second gauge down is a digital gauge with 1/2 pound resolution. It is only $30, requires no fittings or piecing things to together. And, you can still use it as a tire gauge, no need to cut, splice, or dice. ;-)
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Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 52 year old fat man.

Look under the hood when the car hot just after shutting off the motor - you may not be able to see where the coolant is leaking because it evaporates right away - hence no drips. Look for moisture.

Ron
93 245

Would help to know what model this is.

Look for a "salty/crusty" looking residue around all of the coolant fittings.

-Ryan
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Athens, Ohio
1987 245 DL 314k, Dog-mobile
1990 245 DL 134k M47, E-codes, GT Sway Bars
1991 745 GL 300k, Regina, 23/21mm Turbo Sway Bars

Have you done cylinder compression test to see if you are "burning" it up if it doesn't show.
I thought I read here once on the BB that you could pressurize your resevoir I think it was on the 700. Do a search.
Good luck finding it.
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EJO now a 1993 944T 211K