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Coolant leaks - cheap fix info!

54K views 180 replies 89 participants last post by  jon.k 
#1 ·
For all you folks with SVTs that leak coolant near at the thermostat housing area (if you don't have it now, you will!), here's what was wrong with mine - and how you can fix yours for $1 in 10 minutes.

There are two ports in the plastic thermostat housing that use a small O-ring to seal the port. One is the temperature sensor coming out of the top, and the other comes out of the bottom at a 45 degree angle - mine was just an aluminum plug. Mine was leaking at this plug whenever it got really cold. Some folks have leaks at the temperature sensor, same problem. Once hot, it didn't leak.

The problem is that Ford saved about $0.50 by using a Buna-N (Nitrile) O-ring to seal these ports
. Buna-N is only good for a MAXIMUM 230°F service. The engine runs constantly at just about that temperature, and hotter when you shut down after a long run on a hot day. So after a few years, these O-rings get hard and don't seal.

So, rather than pay $60 for a thermostat housing, and/or $10 for a plug (or a fortune for the dealer to fix it, if he ever does), here is what you need to know:

You need a #203 O-ring, made out of VITON. Viton is good for 450° service. Lots of places to get them. McMaster-Carr is just one (have to buy 25, costs $6).
 
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#127 ·
I ordered the Viton O rings from McMaster. Thought I got the wrong size because the o-ring didn't totally fill up the grove on the plug. when I installed the plug it could rock back and forth. Was surpised that it didn't leak. Now 1 week later no leak so I guess it was the right one. The plastic bag that o-rings came in labeled "75 Viton size-3x7 qty-10". I have extras if some one needs one.
 
#130 ·
If I had 300 to spend on that I would consider the above housing, but However, at this time its not feasible.

Does anyone have the part number for the sensor #109 0-ring? I want to order some up and want to make sure I order the right ones.
 
#133 ·
That I can say is a no. Those rings are not rounded, but square. I dont think they will work.
 
#135 ·
Where in Canada are you located? PM me if you like, maybe I can help!
 
#139 ·
Can someone confirm that the #203 is a METRIC size? It makes a difference and might be why some people are having a tough time getting the o-ring over the plug. I beleive the SVT engines use metric fasteners, and the o-rings may fall into that line, as well.

Would it be a Metric #203? And does the snap ring on the lower plug pull towards the front of the engine to remove?
 
#140 ·
Part of the reason the #203 oring is tough to get in is the harder Viton compound - a softer formulation would be better but I haven't found one. The "#203" defines the dimensions, metric or otherwise. When I came up with the #203 it was based micrometer readings of the factory oring and my calculations of oring volume and squish guesstimates.

So whether or not the #203 oring is exactly what Ford used, I can't guarantee. It could be Ford made one specifically to other dimensions. But the #203 designation defines the oring and it was the closest I found anywhere.
 
#141 ·
So, is there a difference between 'metric' and SAE? Is one #203 the same as another, or does it matter? I've read where some guys put an o-ring on, then find the housing later splits. I'm guessing its because the new o-ring is causing stress in areas not bade to do such.
 
#142 ·
A #203 O-ring is defined - every #203 o-ring has the exact same dimensions, by standard. Here is a table of dash numbers:
http://www.mcmaster.com/param/html//Oringsize/9452kac.pdf

The housing has been known to crack even with the factory O-ring - putting a slightly harder Viton o-ring in place of the factory O-ring or even a fresh factory ring that has new resiliency does indeed put more stress in that area and may accelerate a crack failure that has already started. But I don't think the o-rings themselves cause any housing cracks - I think the thermal movement of the attaching plumbing causes high local stresses and cracks the housing in the weakest area - which also happen to be the hole cutouts for the o-rings.
 
#143 ·
It's back - puddle on the driveway. Lasted 5 years. I suspect the housing is cracked this time.

Since I have to pull the whole thing, this time I am simply going to use a smaller O-ring and RTV the whole aluminum plug into the housing. Then the only leak potential besides another cracked housing is the temperature sender plug. Might as well eliminate one failure mode while I can............
 
#144 ·
expect to see this
 
#145 ·
i just spent all of $6 for a junkyard housing out of an I4 Mystique. It has the screw in type water temp sensor and another sensor at the bottom (where the Aluminum plug goes for the SVT housing). I just shrik tube wrapped the unused sensor.

It seems that the inner plastic rib (the one that typically fails) on the JY unit is stronger and your current pigtail for the water temp sensor clips right on to the water temp sensor. The housing even has the correct angles on the nipples for the coolant hoses, with the exception of the main one at the thermostat cover. A unit from an Escort ZX2 will also work; you will just have to change the thermostat cover itself so you get a straight nipple for the main coolant hose. (The ZX2's has a 90 degree nipple).

Time will tell how well this holds up but it is made from a different material and my bet is that it is stronger than that used on the Focus' Zetec, and as you know both the Mystique and ZX2 are also equipped with Zetec 4cyl mills) so the bolt pattern and orifice ID are the same as for the Focus.

And it definitely beats the cost of the other replacement options!!
 
#146 ·
I'm having this problem but I'm not sure if the leak is coming from the same place as the whole O-Ring thing. I was just under the car and watched an orange drop work its way down a black tube and eventually drip out onto the ground.

Here's a view from below. You can see the little orange drop towards the top right of the pic, although I can't say I could tell exactly where it originated...
http://i111.photobucket.com/albums/n133/buskerdog/Image146.jpg


and here it is from above:
http://i111.photobucket.com/albums/n133/buskerdog/Image142.jpg
You can see the little drip working its way down.

What should I do?
 
#147 ·
first of all - change your coolant . immediately. these cars should run on the green type coolant. It even has a label on the degas bottle showing you to NOT use yellow coolant (i know yours is not yellow but orange, but just in case i would change the coolant.

And yes, you're just seeing the drop work its way down to the hoses coming off the thermostat housing. I'd bet you have the same old coolant leak from the housing...
 
#148 ·
Yikes, it's been orange since I got the car 5 years ago (sold to us by a relative's ford dealership. Nice, huh?) So it needs GREEN coolant? Really? Crap.

Ok, and is there a good picture of what the thermo housing looks like etc? I'm having a tough time figuring out what exactly to do. Thanks for the help...
 
#153 ·
Gonna give this a shot today. I got a pack of assorted Viton o-rings at Standard Auto Parts. The thing that sucks is I have no way of knowing which one is which # so I'll just have to measure them I guess. If I can't figure it out I might need to try to buy some from you guys.

It's a shame that there's no steep-by-step in here after all these years and the images that someone hosted on Earthlink are long gone. But I'll give it the ol' college try.
 
#154 ·
I return with my tail between my legs. After spending a half hour trying to figure out how to approach this thing I need more help.

First off, my "assortment" pack of o-rings is just no good for a beginner. I have no clue which to use and the list of sizes (by mm) doesn't line up with the specs I'm finding for the rings I need. I think I need a 203 and a 109 from someone on this board. Any left? The link no longer works.

Secondly, could someone please detail what the heck we're supposed to do? I can't reach any of the tubes that are coated in sticky drips. I also am not sure how to unclip them once I do reach them. I've looked for a "dummies" version of how to do this online but am not finding one. If I have to do something like this: http://www.focushacks.com/?modid=59&ht=Replacing the thermostat and/or thermostat housing then I doubt this is something I can do myself...

Thanks in advance for your undoubtedly brilliant and detailed responses! :D
 
#155 ·
crimp the constant tension clamps and slide them off the hoses. there are 3 of them. you can do it, takes a bit of 'tweaking' to make sure you can slide the clamps off while applying the tension. then remove the three 10mm bolts that hold the thermostat housing to the cylinder head and you will be able to remove the housing from the motor. it IS cramped in there but if i can do it (i got ogre hands) then you should be able to as well.

the clamps can be 'set' to an 'open' position if you squeeze enough. i prefer to replace them with regular hose clamps once im there..
 
#157 ·
Did this fix today as its starting to get cool at night, and I was leaking for sure last year. I had to trim the #203 (which I got from McMaster) a tad with an x-acto, but after the trimming it went right in. I have 24 more O-Rings if anyone needs any. I may keep a couple as spares but the rest are up for grabs. PM me or something.
 
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