First of all, I can't say about Jasper, but from my ten years at a very nice Chrysler dealership, I can tell you that as long as the intermittent problem was documented while under warranty, meaning the dealer had written up a repair order to look into it, Chrysler would still cover it years after the warranty expired when it finally acted up enough that it could be diagnosed. I would at least call Jasper and explain the problem, then see what they say. I really haven't heard anything bad about the company so my guess is they're more concerned with your satisfaction and repeat business than GM is.
A cooling system pressure test is probably not going to be of value for this kind of problem. There will be pressure on the system when the engine is running, and if there's an external leak, it's going to show up as something wet on the engine after driving for a while. I suspect the hydrocarbon test is with the glass cylinder with two chambers partially-filled with a dark blue liquid. That liquid will turn bright yellow if combustion gases sneak into the cooling system. That's not foolproof because you would likely see white smoke from the tail pipe at the same time. If you don't, it's also possible the coolant only goes into the cylinder from the pressure in the cooling system right after a hot engine is turned off. Once the cold engine is restarted, that coolant may just evaporate and leave the tail pipe and not be noticed.
A better test for that, especially when the coolant loss is relatively slow, as in this case, is to add a small bottle of dark purple dye to the coolant, then search a day later with a black light. The dye will show up as a bright yellow stain that you can follow back to the source. If a head gasket is leaking, you'll find the dye inside the tail pipe. Auto parts stores have the dye for the fluid being checked, and those that rent or borrow tools will usually have a black light.
Don't worry about a cracked cylinder head. There were some engines that commonly developed cracks and they were known to not cause a problem so they could be ignored. A warped head is more likely, but a head gasket can corrode through too. Every manufacturer has had problems with leaking head gaskets, and the aftermarket suppliers have done a real good job of coming up with better-sealing gaskets than the originals, and better surface prep recommendations to cause the gaskets to bite into the sealing surfaces better.
Start with the dye, then if you find it in the tail pipe, you may be able to identify the cylinder by removing the spark plugs and shining the black light in there or looking at the plugs' electrodes. I would think that would be enough proof for Jasper to get involved.
Thursday, July 23rd, 2015 AT 8:35 PM