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Working on a 2006 Saab 9-3 2.0 turbo [engine is very similar to the ecotec engines used in the 2006 Chev Cobalts (as an example) where the water pump is timing chain driven].......I am hoping to find an answer in the post to the theoretical question of:
"is it possible for a water pump to pressurize a coolant reservoir the way a leaking head gasket would with combustion gases?"
I do understand that the thermostat as well as a bad reservoir coolant cap could cause these pressures as well. Nevertheless, with all things normal within the cooling system (excluding a failing water pump), could a bad water pump cause similar pressures like a failing head gasket could in the coolant reservoir. Thoughts appreciated and thanks in advance.
I'd say it's unlikely unless there is also a fault with the PCV system. If the crankcase is getting pressurized that gas might could get into the cooling system via the waterpump.
The only way a coolant reservoir gets pressurized would be
1. its meant to be as its cap has a pressure rating and seals the reservoir like in systems that the radiator does not have a fill cap.
Edit : bad coolant cap would result in excessive pressure ie over 14 -16 psi
2. Headgasket failure sending exhaust gases into coolant sys. Making it look like coolant is boiling in reservoir.
3. Coolant is old / too diluted with water causing water to boil off/turn into a gas state.
If I understand your question correctly, then I would generally say no. Failed water pumps won't create an artificial increase in cooling system pressure.
What kind of water pump failure did you have in mind? Leaking externally? Worn impeller? Broken drive belt/chain?
More often, I see water pump failures causing no circulation in the cooling system, causing the coolant to boil over.
To give a little more insight on my particular problem.... there is a leak by the water pump and pressure in the reservoir.... I believe I have to problems going on here. Vehicle can idle in the shop all day - no overheating. Drive the car (i.e. change the pressures in the cylinders) and car usually overheats depending on how hard you drive it. Again, I sincere believe I have two issues here - 1) screwed up head gasket when cylinder pressures are higher and 2) leaking water pump or seal near water pump.
The confusion / voices in my head where suggesting "maybe the water is slipping or not spinning fast enough under load". But what I thinking you are saying Tyler is "a water pump is not a pressure source in the coolant reservoir. Rather, combustion gases, faulty thermostat, faulty rad cap, and potential PCV pressures leaking into the cooling system are pressure considerations."
No, I do have pressures in the coolant reservoir.... as per Tyler's post.... I have a little more insight as to what to consider for likely pressure causes in the coolant reservoir.
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