Northstar Engines and System Technical Discussion Discussion, where is thermostat in Cadillac Engine Discussion; The purge line IS the air bleed line. It "purges" air from the cooling system....
Automobile(s): 2002.5 F55 STS, 2014 Explorer XLT 4WD
MD Eastern Shore
Re: overheating and no heat
ecoleman, In your Deville the coolant reservoir is over on the passenger side. The purge line runs around past the P/S pump, under the engine cover, and over to the hollow bolt/nipple at the water crossover - right next to the water pump cover where you changed the thermostat.
That line should flow a constant small stream of coolant into the reservoir. It is at the high point of the cooling system and so bleeds off air from the main system to prevent water pump cavitation and loss of coolant flow.
To test the purge system with the engine cold, remove the small hose from the side of the reservoir, remove the pressure cap and have an assistant start the engine normally while you hold the hose in the open reservoir neck - you should have a steady coolant flow. If not, you need to remove the entire hose/piping and clean it out, and use a suitable sized drill bit, hand turned, to clean out the metal nipple/bolt on the engine. IF the purge lne cannot be unclogged it can be replaced with a length of proper sized fuel hose - that has a braid jacket and will withstand the 16 psi cooling system pressure: The entire system is under pressure when the cap is installed.
Proper cold coolant level is about halfway up in the reservoir - follow that arrow across the top and down the sie of the reservoir.
Automobile(s): White Diamond '03 DHS (with DTS floor shift)
Re: where is thermostat
You also need to clean out the hollow bolt that the purge line attaches to at the other end. If the line was clogged with that sealant tab residue, then the hollow bolt surely is and you will still be overheating.
DO NOT use those damned sealant tabs anymore.