I'm looking for an answer to an almost 2 year old question about my '03 Marquis. I am going to link another thread that gives some unrelated yet possibly relevant info about this car at the bottom of this post. But the issue at hand is a strange one. It's two years now because I've had the mindset of "if it ain't broke, don't fix it." But I now want the fix and peace of mind...
The car has been running very well for the last 2 years I've maintained it (5 months owning it). In two years, it has NEVER been hot on the gauge. I've even driven 600 miles one-way in one day. But before and after changing the intake manifold, thermostat, radiator cap (Motorcraft), and a coolant flush, the coolant will NOT build pressure. I can literally run it 600 miles/10 hours straight, pop the hood, and take off the radiator cap very quickly. I'll barely get a wheeze, much less a hiss. But again, no overheating either. There's no evidence of weeping, and definitely no coolant loss at all. And I have pressure tested the system, no problems there either.
My initial thought was thermostat, of course, but this is the second one and still nothing. Surely it's not clogged anywhere because that would definitely cause an overheat. And a stuck thermostat makes no sense open or closed, because the car warms to normal temp quickly as it should.
So what could possibly be the culprit here?!? My only wild guess (thanks to a trusted mechanic) is the water pump, but we both agreed it's extremely slim odds. I'll be changing the pump this week, just to eliminate the variable. And I refuse to accept a counter jockey's answer of "it won't build pressure because the cap is on the expansion tank." So what's the point of the pressurized cap then?!? It HAS to build pressure. But if the water pump doesn't solve it, I'm going to lose my mind. And I know, it sounds literally impossible, and even I doubt my evidence/facts, but it's the truth. I swear!
HUGE thanks in advance for help!
Unrelated Yet Relevant Info Link
The car has been running very well for the last 2 years I've maintained it (5 months owning it). In two years, it has NEVER been hot on the gauge. I've even driven 600 miles one-way in one day. But before and after changing the intake manifold, thermostat, radiator cap (Motorcraft), and a coolant flush, the coolant will NOT build pressure. I can literally run it 600 miles/10 hours straight, pop the hood, and take off the radiator cap very quickly. I'll barely get a wheeze, much less a hiss. But again, no overheating either. There's no evidence of weeping, and definitely no coolant loss at all. And I have pressure tested the system, no problems there either.
My initial thought was thermostat, of course, but this is the second one and still nothing. Surely it's not clogged anywhere because that would definitely cause an overheat. And a stuck thermostat makes no sense open or closed, because the car warms to normal temp quickly as it should.
So what could possibly be the culprit here?!? My only wild guess (thanks to a trusted mechanic) is the water pump, but we both agreed it's extremely slim odds. I'll be changing the pump this week, just to eliminate the variable. And I refuse to accept a counter jockey's answer of "it won't build pressure because the cap is on the expansion tank." So what's the point of the pressurized cap then?!? It HAS to build pressure. But if the water pump doesn't solve it, I'm going to lose my mind. And I know, it sounds literally impossible, and even I doubt my evidence/facts, but it's the truth. I swear!
HUGE thanks in advance for help!
Unrelated Yet Relevant Info Link