WHAT ENGINE is in your van? C.I. displacement? 4, 6 or 8 cylinders? Transmission? (Auto or standard). HOW MANY MILES? A pressure test of the cooling system quite often reveals a blown head gasket by several pieces of evidence. A competent mechanic can do this test and explain what results he got. Get a compression test done on all cylinders. They should all read within 10% of each other. I typically take the mid-range reading and add or subtract 10%. If that is true, then a mechanical failure of internal engine parts can be set aside for the moment. If the van has around 100K miles, time to do a fairly thorough check-up on the van. Check the injectors for their properly-specified resistance readings. If one is way out of whack, then replace just that one injector. Injectors don't necessarily relate to compression, but what the heck---might as well do this check to reduce potential future surprises. At $80+ a pop per injector, just don't tear all of 'em out and replace them all. If the injectors are all within specs, then it's time to check out the rest of the fuel and electrical systems. You just might have only one injector that needs replacement. But start with a compression check on each cylinder. Have whoever does the work write down his original findings. Then YOU can determine what the proper compression range is for that specific engine. Might be as simple as a stuck oil ring. A couple of teaspoonfulls of Marvel Mystery Oil in that cylinder left overnight just might be all that you need to free up a sticking oil ring. After putting the MMO in that cylinder, just crank the engine 1 revolution. That'll get the MMO up against and into the oil ring. Though the compression rings are supposed to control the compression, some of those have been known to stick. Either way, MMO just might be all that you need. MMO won't help with more major component break downs like the valves,head gasket, etc. A shot of (a couple of teasponns) of regular motor oil poured into the weak cylinder will give you a clue as to the functioning of the compression rings. Check the weak cylinder, add the motor oil, re-do a compression test on that cylinder, and if the compression comes up and then drops after a few revolutions, then it's probably rings or valves. Eliminate the easiest thing first and move on down the list. But a thorough compression test is where you start. If your guy can't/won't tell you why you have low compression, find someone who WILL tell you and continue troubleshooting until he can pinpoint the most likely cause. For instance, a cooling system pressure test will help determine warped head/blown head gasket situations. Then get into the more difficult troubleshooting aspects until you've either eliminated or repaired what REALLY needs to be done.