Hi, and welcome. My name isXXXXX you give me some background on this problem?
Several days ago I made the mistake of starting my 1999 Jag XJ8 and driving it across the street into my garage. I shut it down without letting the temp rise to operating level. After the weekend I came home and tried to start it. The engine did crank vigorously and seemed like it had no compression. It spun freely. I towed it to a local shop, and they tried. They recommended a new engine. I consulted the Jag Forum and learned about "bore-wash" and suggested the mechanic try a compression test. The plugs came out for the first time in 118,000 miles and the test resulted in no compression in any cylinder. I suggested oil in each cylinder and try again. No result. They want to install new plugs and try it, and I stalled thinking it would be a waste of $200 with no compression. I have owned this car for 2 years+, bought it used with 86,000 miles and it never failed to start. Some oil shows up in the air filter, but it seems very minor, so maybe there is some blow by. The previous owner changed the oil religiously with Mobil 1, and during my ownership I learned it leaked or used about 1 qt between changes. It ran good, until it didn't run and that was all kind of sudden. I'm not willing to spend $1,000s on a replacement engine, and my high hopes are I screwed up and caused bore wash. I need to know how to correct it and get the car running.
Ok, based on what you are telling me I agree with the cylinder washing. I don't think the shop oiled the cylinders properly. They need to squirt about 8 squirts of motor oil into each cylinder and the put the spark plugs back in and try to start it. You need the plugs in there to help force the oil back around the piston rings. They also need to make sure that they have a strong battery in the car when cranking the motor. I've repaired dozens of these for this problem and I seriously doubt that you need a new engine. With a little persistence you can get the compression back and should be fine.
Also, installing new plugs is a good idea if the original plugs are still in the car. Let me know if you need any more help with this.