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#4423729 - 06/06/17 04:07 AM Ford 4.6L Coolant Pressure Mystery
tony1679 Offline


Registered: 06/08/14
Posts: 617
Loc: Central Oklahoma
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
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#4423733 - 06/06/17 04:25 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: tony1679]
Lubener Offline


Registered: 01/22/11
Posts: 2574
Loc: N.Ohio
That cap on the resesvoir should be checked, that tank is pressurized on your G.M.. Don't waste your time with the water pump unless it's weeping. Listen to your counter jockey, it's a cheap part compared to the water pump.Face it, your have a leak somewhere, bleeding off the pressure.


Edited by Lubener (06/06/17 04:26 AM)
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#4423738 - 06/06/17 04:47 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: tony1679]
tony1679 Offline


Registered: 06/08/14
Posts: 617
Loc: Central Oklahoma
Originally Posted By: Lubener
That cap on the resesvoir should be checked, that tank is pressurized on your G.M.. Don't waste your time with the water pump unless it's weeping. Listen to your counter jockey, it's a cheap part compared to the water pump.Face it, your have a leak somewhere, bleeding off the pressure.

The cap... The initial cap was bad. So I bought a Motorcraft replacement. When I still suspected it, I exchanged it for a THIRD Motorcraft cap. It's not the cap unless I hit the unlucky lotto of 3 bad ones in a row.

Agreed on the pump, but $30 for a brand new (not reman) replacement pump with a lifetime warranty was a no-brainer. And pumps on these are a breeze to change, so why not roll the dice?

And I can 100% assure you there is no coolant leak anywhere. I've kept track of the coolant level (even marking it). It hasn't moved a millimeter in 2 years. Nothing in the oil, nothing on the driveway. Nothing dripping down the motor (just changed the oil again 2 days ago). Not sure what leak I'm facing...?

Perhaps you're referring to an air leak? I feel I disproved that by pressure testing the system. It held within 1 p.s.i. for 45 minutes.

I sincerely appreciate your input. However, I still think the problem is elsewhere.
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#4423764 - 06/06/17 05:51 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: tony1679]
Ethan1 Offline


Registered: 12/29/14
Posts: 1632
Loc: 'murica
What you're describing is normal.

Also, how could the water pump cause this? And how could the car run perfectly with a bad water pump?

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#4423772 - 06/06/17 06:05 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: Ethan1]
tony1679 Offline


Registered: 06/08/14
Posts: 617
Loc: Central Oklahoma
Originally Posted By: Ethan1
What you're describing is normal.

Also, how could the water pump cause this? And how could the car run perfectly with a bad water pump?

Agreed, to a point. A water pump surely is NOT the culprit, but I've changed virtually everything else. For $30, I'll take an unnecessary shot in the dark. The factory pump has served 125k already. Why not?

But I'm confused how a pressurized cap on an expansion tank without any pressure building in it is normal...? shrug
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#4423795 - 06/06/17 06:59 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: tony1679]
HoosierJeeper Offline


Registered: 11/23/16
Posts: 1276
Loc: WI
I'd replace the cap.

Or at minimum test the old one.
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#4423797 - 06/06/17 07:03 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: tony1679]
Cujet Offline


Registered: 02/15/03
Posts: 7139
Loc: Jupiter, Florida
My guess is that somewhere, a the top of the system, air is allowed to escape. You very likely have a healthy cooling system and engine. The pressure builds due to expansion of the water (and air) in the system when hot. If the cooling system is not being taxed, a small air leak will prevent pressure buildup. The existing coolant will expand a bit and all will be well.

Also, if your hoses are really soft, they could expand a bit and reduce system pressure. But not likely to create a zero pressure condition.

Try bleeding all air from the system and see where the leak is.
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#4423807 - 06/06/17 07:09 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: tony1679]
Trav Offline


Registered: 11/20/06
Posts: 18827
Loc: MA, Mittelfranken.de
Start by testing the cap and pressure testing the system, this is a very easy issue to diagnose.
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#4423850 - 06/06/17 07:58 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: tony1679]
meep Offline


Registered: 02/20/07
Posts: 3548
Loc: Southeast
the 1 psi pressure test performed above is not adequate. 14-15 psi is probably a better test. I'd test it at whatever pressure the oem pressure cap is rated at.

My S60 has very soft hoses. They all do. And it uses a sealed system where the reservoir itself is pressurized and has the bit of air stored in the top of it too. But when it's at temp, all of the hoses are rock hard. I would expect the same in the 4.6.

You have a tiny leak somewhere, but you are not straining the cooling system enough to start boiling fluid.

-m
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#4423896 - 06/06/17 08:48 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: tony1679]
Miller88 Offline


Registered: 04/09/08
Posts: 12698
Loc: Onondaga County
I recently changed the intake manifold on the F350 and there are a few ports on the coolant crossover that can be opened up (either for the various temp sensors or maybe bleeding), is it possible that you are losing some coolant and air through that?

Or have you checked the coolant bottle itself? There could be a hairline crack in the seem that you are not seeing.
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#4423943 - 06/06/17 09:55 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: HoosierJeeper]
tony1679 Offline


Registered: 06/08/14
Posts: 617
Loc: Central Oklahoma
Originally Posted By: HoosierJeeper
I'd replace the cap.

Or at minimum test the old one.
I have twice already. I mentioned it earlier in this thread.
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#4423950 - 06/06/17 09:59 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: Cujet]
tony1679 Offline


Registered: 06/08/14
Posts: 617
Loc: Central Oklahoma
Originally Posted By: Cujet
My guess is that somewhere, a the top of the system, air is allowed to escape. You very likely have a healthy cooling system and engine. The pressure builds due to expansion of the water (and air) in the system when hot. If the cooling system is not being taxed, a small air leak will prevent pressure buildup. The existing coolant will expand a bit and all will be well.

Also, if your hoses are really soft, they could expand a bit and reduce system pressure. But not likely to create a zero pressure condition.

Try bleeding all air from the system and see where the leak is.
Thanks for actually reading and giving your input. I'll replace the hoses too (not much to lose at this point), but I highly doubt there is air trapped. It's had the coolant flushed at a shop (prior to owning it myself) and it's had 2 years since then to burp. I've never had this much difficulty with coolant. Usually it's very black and white.
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#4423954 - 06/06/17 10:02 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: Trav]
tony1679 Offline


Registered: 06/08/14
Posts: 617
Loc: Central Oklahoma
Originally Posted By: Trav
Start by testing the cap and pressure testing the system, this is a very easy issue to diagnose.
I have already stated earlier in this thread that I did. 3rd cap and pressure test passed...
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#4423958 - 06/06/17 10:06 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: meep]
tony1679 Offline


Registered: 06/08/14
Posts: 617
Loc: Central Oklahoma
Originally Posted By: meep
the 1 psi pressure test performed above is not adequate. 14-15 psi is probably a better test. I'd test it at whatever pressure the oem pressure cap is rated at.

My S60 has very soft hoses. They all do. And it uses a sealed system where the reservoir itself is pressurized and has the bit of air stored in the top of it too. But when it's at temp, all of the hoses are rock hard. I would expect the same in the 4.6.

You have a tiny leak somewhere, but you are not straining the cooling system enough to start boiling fluid.

-m

You misunderstood, but I didn't exactly clarify. It lost less than / stayed within 1 p.s.i. over 45 minutes of pressure testing. The cap is rated at 16 p.s.i. and that's the pressure it was tested at.
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#4423962 - 06/06/17 10:13 AM Re: Ford 4.6L Coolant Pressure Mystery [Re: Miller88]
tony1679 Offline


Registered: 06/08/14
Posts: 617
Loc: Central Oklahoma
Originally Posted By: Miller88
I recently changed the intake manifold on the F350 and there are a few ports on the coolant crossover that can be opened up (either for the various temp sensors or maybe bleeding), is it possible that you are losing some coolant and air through that?

Or have you checked the coolant bottle itself? There could be a hairline crack in the seem that you are not seeing.
Thanks for the input. I'm not sure, I'll have to look later as it's not the factory intake. It's a Dorman replacement (working well btw).

As for the tank, I have looked many times (but never with it out of the car, so I may overlook one every time). However visual inspection aside, if it lost less than 1 p.s.i. over a 45 minute pressure test, I highly doubt there is a leak. shrug
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2003 Mercury Grand Marquis LS Ultimate Edition
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