Hi

Patient: Volvo V60 2.0 Diesel 5 cylinder - 372000km
One day I noticed after driving about 80km that the low coolant level warning appeared on the dashboard. I pulled over and noticed that the level was 1.5cm below min instead of normal between min and max.
I carefully started to unscrew the cap of the expansion tank to top it up. But then the cap hissed and the water level rose back to max.
We drove another couple of miles, but then the phenomenon started all over again. First the warning only flashed at roundabouts, then continuously.
Stop again, cap off, hiss, level restored.
What I have noticed so far:
- The fluid is not draining from the system
- No oil film or indication of oil film in the reservoir
- No emulsion on the cap of the oil filler cap
- Accumulated pressure in the tank remains for up to one night.
- Car does not emit white smoke in the morning or at other times
- No loss of power or boiling water, engine does not overheat, all temperatures are normal
- No exhaust smell when smelling the coolant
- The radiator cap has been replaced, but nothing has changed significantly
- On the tank breather, excess pressure is not vented from the system


Does anyone have any ideas?

 

next step would be to have a shop actually measure the coolant system pressure. Too much coolant system pressure may point to a head gasket issue where exhaust gasses are finding their way into the coolant system raising the pressure. Does the upper radiator hose get rock hard when the engine is warm/running? There's also HC test kits that sample the coolant for the exhaust gasses, also typical test for head gasket fails.

 

Just today we did an indicator fluid test, which in theory should show if there is exhaust gas in the coolant. The colour of the fluid is blue and if it comes into contact with exhaust it should change to green.
The test was run with the engine running for several minutes, but the fluid colour, not a bit changed. In order to test the quality of the fluid, we drove the exhaust directly into it and it turned green in 3-5 seconds.

My mechanic still claims that the cylinder wall is cracked between cylinders 2 and 3, and that's where the gas is being worked into the system under compression. I just don't understand, if gas can get into the system during the compression stroke, why this doesn't happen during the working stroke when the pressure is much higher. Because then the indicator fluid would be saturated.

 

I'm not sure how he's assessing a crack without tearing down the engine vs a head gasket issue but both are pretty much saying time for a replacement engine :-(

Given the $$ involved here it may be worth going to a second shop (dealer) for that second opinion.

 

I have consulted my Volvo expert mechanic and have just received a detailed explanation.

1. 90% of the block is cracked, most likely between cylinders 2 and 3 at the top edge of the cylinder wall.
2. why no exhaust gas in the water circuit? It is because there is no exhaust gas in the compression phase of the cylinder when there is no exhaust gas, just plain air. In the last 10% of the stroke, when the pressure is high enough (about 20 bar), the air is squeezed into the piston crack. Then comes the injection, which creates the explosion in the cylinder chambers. But at this point the piston is just at the dead center, so the piston almost covers the crack. Then in the working phase when the piston starts to go down, the gas pressure drops, the crack is no longer open enough for gas to flow in.
3. Why does the engine not consume water? The crack is so small that it is now acting as a valve, like a heart valve. The concave surface on the inside is easier for gas to push apart than water on the outside, and the more it is pressed against the wall, the more it closes (for now). So there is only one direction, gas out of the cylinder.

The method of repair is to have the cylinders "bushed" at a specialist engine repair shop.
They bore the cylinders and put similar 5 cylinder VW engine "sleeves" in the engine, which are much more durable.

 

Hi

99% of the engine block is cracked. Based on preliminary data, there is a crack about 2-5mm at the top edge of the cylinder wall.
According to my mechanic, these are the explanations for the phenomenon:
- no exhaust gas in the equalization tank = No, because air is introduced from the cylinder into the water chamber when the cylinder is moving upwards at the compression stroke, and when the pressure rises dramatically. And no gas oil gets into the system either, because by the time the injector does its job, the piston is already at a dead stop and almost plugs the crack, thus blocking it.
- What happens during a work stroke? = This is when the self-ignition typical of diesels takes place, but it's actually in the piston chamber, there's no exhaust gas pressure reaching the cylinder wall, and as the piston moves down, the pressure drops.
- Why is the water not running? First, the crack is still very small, and second, the crack acts like a valve. Pressure from the inside can open it, but from the outside it can keep it closed because the water is pressed against a convex surface.

Translated with DeepL.com (free version)

 

Well, for now, I'm devastated. At the moment, using the car is essential for me, but the bigger problem is that the final cost of the repair is well beyond my financial means. Here in Hungary the repair costs about 2 million HUF, which in Euro is about 5000.
I have no idea how to scrape together that much money????