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Has It Been That Long?
11,996 Posts
Discussion Starter #1 (Edited)
A common issue we're seeing is that the coolant cap design for the recovery tank was faulty from the factory. The cap will fail without warning, causing significant coolant loss.

ALL Ford dealerships and vendors were instructed to return the obsolete design so they could be destroyed, so the caps in the parts chain are all the new design.

NOTE: At some point Ford started to use the new cap design on the cars coming off the line. I would hazard a guess that 2013 on would have the new cap. Doesn't hurt to check using the pictures below. Also, your older car may have had it replaced by the previous owner.

This was the old cap design on my 2003 (yours may look different)

This is the new cap design (standard across all models)

Here's a pic to help further determine if you have the bad cap (credit to user Chartmaker)

The part number for this Motorcraft part is RS-527.

It fits these Ford models and years:

FORD E-150(1995 - 2014)
FORD E-250(1995 - 2014)
FORD E-350(1995 - 2014)
FORD E-450(2000 - 2014)
FORD E-550(2002 - 2003)
FORD EDGE(2007 - 2014)
FORD EXCURSION(2000 - 2005)
FORD EXPEDITION(1997 - 2008)
FORD EXPLORER(2002 - 2014)
FORD F-150(1997 - 2014)
FORD F-150 HERITAGE (2004)
FORD F-250(1997 - 1999)
FORD F-250 SUPER DUTY(1999 - 2014)
FORD F-350 (1997)
FORD F-350 SUPER DUTY(1999 - 2014)
FORD F-450 SUPER DUTY(1999 - 2014)
FORD F-550 SUPER DUTY(1999 - 2014)
FORD FIVE HUNDRED(2005 - 2007)
FORD FLEX(2009 - 2014)
FORD FREESTAR(2004 - 2007)
FORD FREESTYLE(2005 - 2007)
FORD FUSION(2006 - 2012)
FORD GT(2005 - 2006)
FORD MUSTANG(1996 - 2014)
FORD RANGER(2001 - 2011)
FORD TAURUS(1996 - 2014)
FORD TAURUS X(2008 - 2009)
FORD WINDSTAR(1999 - 2003)
LINCOLN AVIATOR(2003 - 2005)
LINCOLN LS(2000 - 2006)
LINCOLN MARK LT(2006 - 2008)
LINCOLN MARK VIII(1993 - 1998)
LINCOLN MKS(2009 - 2014)
LINCOLN MKT(2010 - 2014)
LINCOLN MKX(2007 - 2013)
LINCOLN MKZ(2007 - 2012)
LINCOLN TOWN CAR(1992 - 2011)
MERCURY COUGAR(1994 - 1997)
MERCURY MILAN(2006 - 2011)
MERCURY MONTEGO(2005 - 2007)
MERCURY SABLE(1996 - 2009)

If your car is on this list, and the cap has not been replaced (or was replaced with an aftermarket unit), I highly recommend you replace the cap. Go with the Motorcraft (aka Ford) part on this one, as the aftermarkets are based on the flawed original design.

There are two easy ways to get the cap.

1. Drive to your local Ford dealer. Ask for the cap. They will likely have it, since it's used on so many models, or they might have to order it. I did this, and it cost me about $13 with tax. Price will vary slightly for you based on tax.

2. Visit RockAuto Parts Catalog and order the cap. Use the latest discount code found on this forum at this link: RockAuto - Taurus Car Club of America : Ford Taurus Forum

The code goes in the "How Did You Hear About Us" box at checkout. The part at Rock Auto was $6.09 at the time I made this post, and with shipping to my house and with the discount (only .30 cents since it's a 5% code) it was $8.23 in total.

This post is for informative purposes only, and should your car detonate, mutate into a swamp-monster, or suffer a problem I am not liable. :lol2:

Prices current as of December 2013.


Don't Be Stupid
7,049 Posts
Curious to know how it fails. My '00s cap seemed to find its way loose a few times. Would pop the hood and find it sitting on the reservoir. Happened at least twice.

Has It Been That Long?
11,996 Posts
Discussion Starter #3
It doesn't hold the 16 psi that it's rated for, and tends to spectacularly fail by blowing coolant out. But other times it will simply leak due to age, but only somewhat.

9,614 Posts
Curious to know how it fails. My '00s cap seemed to find its way loose a few times. Would pop the hood and find it sitting on the reservoir. Happened at least twice.
The cap has 2 valves, one with a heavy spring that releases pressure if it exceeds the rated (16# +/-2). The second is a very light spring and that lets air into the tank when the pressure goes negative. (vacuum) All the system is intended/designed for pressure, not vacuum. Vacuum collapses hoses, pulls the rad tubes in to stress.

As the coolant heats up it expands and that builds pressure necessary to raise the boiling point of the coolant, and also prevent steam bubbles from growing and making dry spaced around the cylinders.

In my case, the pressure cap test showed all is well. Put the same cap on the car and warm it up: feel the larger hose and no pressure. Switch caps with the Sable and warm it up and pressure is fine, tight hose. If I drive it without pressure, I get coolant all over the top of the tank.

Most likely, the vacuum release valve is not sealing and letting the pressure out as it slowly builds in normal warmup of the engine. Quick pressure of the tester seals it. My op: testing is worthless. Cap is cheaper than labor, and the testing does not work.

All the caps tighten with a torque setting clicker rachet. Really quite tight, and my new one takes more torque to click it. New one as I bought 3 and replaced all mine.

Cheap insurance.

And this: my '02 Lin lost it's coolant on a cold Dec night, before we were leaving on a day trip the next day. Had to borrow a car for that. Lin had coolant all over the place. When got a chance, had to wipe all that down in the cold and guess at what was wrong.

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