960 '96 960 - Engine Flooded after sitting for a few weeks

My explanation is that with cold oil the lifters get stuck to max lift position and it takes time(cranking) for them to get set. All that matters is that engine is cold, excluding few cases. Whether its overnight or years the result is the same if engine dies or is shut off soon after starting up. After that there is no compression in all cylinders, not just in one or two. And that happens every time. And there is always compression when cranking and starting up before this.

This issue has never occurred on whiteblocks with solid lifters and I have never seen a stuck valve in any engine though my experiences are limited to Volvos. Neither of the two headgasket jobs mentioned had valves open when the head was off.

It's not also a case of flooding the engine. When the compression returns the car will fire up and run even if the injectors have been connected the whole time.

Getting into the basics of valve lifter operation is necessary to put this theory to rest. Older service manuals used to specify a leak-down rate for a working lifter using a special leak-down tool. A certain amount of weight pressing down on the lifter should take x number of seconds to collapse, and so on. Hydraulic lifters do not "stick open". Even if ALL the lifters in an engine were collapsed, the engine would still start and run. Lifters are just cylinders that hold oil, with a small hole that lets the lifter leak down just enough to take up valve lash.

With the engine stopped, any open valve will apply the force of the valve spring against the lifter plunger, forcing the remaining oil out of the lifter's cylinder and thus collapsing the lifter. The lifter cannot pump up again until engine oil pressure builds up at the next start.

But, since the operating range of the lifter (the difference between a collapsed lifter and a fully pumped up lifter) is small, a collapsed lifter will tick until engine oil pressure builds up, but it will still open a closed valve. Thus we have to focus on those valves that are open when the engine stops. Those are the valves that can remain open if they are stuck, and are not affected by the operation of the lifter or pushrods. Back to the question about why the valves are sticking. That's a pretty serious design screw up and I imagine Volvo would be embarrassed to have it widely known. Just a guess.

The theory that raw gas flushes oil from the cylinders, causing a no compression situation, is really unlikely. Of course after minutes of straight cranking the cylinders are no doubt a little damp, but washed completely of all oil? I doubt it. But the question still remains, why didn't the engine start within the first couple of cranks? The no compression condition exists right away because of stuck valves, not lifters, not timing belt and not raw gas dumped into each cylinder. The raw gas in the cylinder problem is really limited to carbureted lawn-mowers and 2-stroke single cylinder engines.

-L

Lazarus said:

But the question still remains, why didn't the engine start within the first couple of cranks?

-L

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Just like it did happen with OP, engine always fires up at first. After that no compression happens if the engine dies for a reason x or is shut off soon. If the engine is going to die and you are ready for it(you know it has happened to that engine before), you can keep it running with gas and after that it'll settle and run normally.

When taking the head or cams off the lifters seem to keep the oil inside the hydraulic unit and no compression occurs after assembly. But only if the engine has died after cold start or it has been shut off soon(start and drive from outside to the lift). It's a pretty marginal problem considering how many engines there are but still an annoying one.