Head Gasket

Got the van back from the dealership after having the intake gaskets replaced. I just had the sniffer put on the radiator at my mechanic and showing signs of exhaust. Head gasket?

Should this have been picked up on by the dealership when and if they pressure tested the system after replacing the intake gaskets?

The van is not overheating, faint white smoke at start up but disappears, moisture evident out of tail pipe. No bubbles in radiator or reservoir, engine not skipping.

A cooling system pressure test will usually indicate if there is a leak in the cooling system. If the sniffer is detecting CO, (Carbon Monoxide) in the radiator, combustion gasses are getting into the cooling system and confirms a head gasket as a likely cause, although a cracked cylinder head is also possible.

I'm not sure the sniffer test was accurate. I've been watching the coolant level and temp for days now. I have monitored it in the morning during initial start-up. Also been on a few long trips. There is no coolant being lost at all. The tailpipe isn't blowing white smoke or coolant either. The temp gauge that was acting up, by going to the red and falling back when I turned on the heater has stopped doing this as well. The fan is kicking in at 210 and dropping the temp back to 155. There is no loss of power, there are no bubbles coming back to the reservoir, the oil looks great, no foam anywhere, the radiator cap has no whitish substance to it as well. The van is running great right now, I'm going to drive it more and see, I'm also going to have the sniff test again, I think it was wrong but who knows.