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Author: Subject: Zetec 2.0 Expansion Tank Pressure
Plunky

posted on 17/1/17 at 07:03 PM Reply With Quote
Zetec 2.0 Expansion Tank Pressure

Evening all,
I have recently been experiencing an issue with the expansion tank on my blacktop zetec.
I had to replace the expansion tank a little while back as it developed a split.
I replaced with a Renault Clio unit, all was well until I started to get coolant being expelled via the cap.
I have changed the cap to a higher pressure one, however I am still getting coolant coming out of the cap when the pressure builds up.
I went out for a driver earlier, it was fine for around 40 mins, until I slowed down in traffic and the temp increased.
I am not seeing the engine overheat, it just seems to build up pressure after a period of time.
Any ideas?
P.S. it is a brand new crate engine, with about 350 miles on it.
thanks,
Liam

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rusty nuts

posted on 17/1/17 at 08:04 PM Reply With Quote
I believe you may need to fit an idler pulley on the auxiliary belt to get the water pump to rotate in the correct direction? It may be you have an air lock in the cooling system ? Are you using a heater or blanked off heater pipe connections? How is the cooling fan controlled?
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coozer

posted on 17/1/17 at 09:18 PM Reply With Quote
Where is the tank plumbed in? It needs to be in the bottom hose near the rad... guess how I know.....





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Plunky

posted on 17/1/17 at 10:09 PM Reply With Quote
I'm fairly sure that there is no issue with the plumbing side of things as there has never been a problem before I fitted the replacement expansion tank.
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cliftyhanger

posted on 18/1/17 at 05:16 AM Reply With Quote
Have you tried a different cap? could be faulty.

Also noted your previous tank split. What caused that? Too much pressure?

EDIT. Re reading you have already tried a higher pressure cap. There seems to be an issue here, are you overfilling the header tank? If not, and definitely no overheating, I would be getting the coolant "sniffed" to rule out HGF.

Re possible overheating, how are you checking that? has your gauge been calibrated? or used an IR thermometer when the issue occurs?

[Edited on 18/1/17 by cliftyhanger]

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907

posted on 18/1/17 at 08:19 AM Reply With Quote
The pressure at which a cap blows at depends on how much the spring is compressed.

When I made my overflow header tank I copied the cap recess from the Coolman rad that I had bought from Robin Hood,
as it was then.
I bought a QH cap marked up at 11 psi which is correct for the 907 engine but when pressure tested it blew at 4 psi.
As a quick fix for test purposes I placed a 3mm thick rubber washer in the tank cap recess to compress the spring more
and hey-presto it blew at 12 psi.

I have a mate ( just the one ) whose 1600 CF had a similar problem. New cap fitted and a 3 mile test drive. Great.
Didn't drive the car all winter and the first long run in the spring and it boiled. Turned out to be a shorter cap.


HTH
Paul G





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Plunky

posted on 18/1/17 at 08:46 AM Reply With Quote
thanks for all your suggestions.
I really hope it isn't a head gasket failure as it is a brand new engine with very little mileage. There isn't any milky substance in the oil.
The old tank just had a normal screw top cap, no pressure valve in it, which resulted in no issues, apart from it splitting (it did look old and knackered).
Do you think I should try and use a header tank with no pressure valved cap? There is a pressure cap on top of the rad

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907

posted on 18/1/17 at 11:10 AM Reply With Quote
There isn't any point in having two pressure relief caps. It will just blow the lowest pressure one.

You do however need the cap to be at the highest point, otherwise you'll blow out water while the steam
collects at the high point.

I have a flat cap on the rad and a pressure relief on the header tank. The 6mm rad overflow is linked in
to the top of the header so the rad remains 100% full.

Paul G





The one and only member of the Suttol Owners Club. Now also the MX5 Owners Club. A few more in that one.

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r1_pete

posted on 18/1/17 at 01:59 PM Reply With Quote
Did you replace the tank like for like?

A long shot but are you sure you havent connected the air bleed hose from the engine to the overflow above the pressure cap seat?

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Plunky

posted on 18/1/17 at 02:35 PM Reply With Quote
quote:
Originally posted by r1_pete
Did you replace the tank like for like?

A long shot but are you sure you havent connected the air bleed hose from the engine to the overflow above the pressure cap seat?


No, I didn't replace like for like.
The old tank looked rubbish and had a poor mounting design, so I used a clio one as it could be mounted better.

How do you mean 'above the pressure cap seat'? Do you mean is the overflow above the pressure cap on the rad?

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r1_pete

posted on 18/1/17 at 03:06 PM Reply With Quote
Yes, it'll come out of the neck just above the seal surface, probably about 8mm dia.
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Plunky

posted on 18/1/17 at 04:05 PM Reply With Quote
I've attached some pictures to show the set up.
If anyone notices anything that could be causing the issue then please do shout!
Thanks,
Liam










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Paul Turner

posted on 18/1/17 at 05:09 PM Reply With Quote
Is that a blank cap on the radiator or another pressure cap. You should only have one pressure cap in the system, with 2 it won't work correctly.

This is how mine is plumbed and its worked perfectly since 2002 with both Silvertops and a Blacktop with one exception. Fitted a cheap (150 from a burnout) 2 litre which initially actually ran beautifully but the headgasket failed after a few hundred miles, expansion pressurised and made a right mess. New headgasket and 1/2 day in the garage sorted it.




You say you hope its not the head gasket since its a brand new engine with low mileage. Personally I would not expect a problem with the engine but be aware that the last of these Zetecs was actually built in 2004 and they have been stood in warehouses ever since. So whilst its low mileage it coming up 13 years old at least.

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mcramsay

posted on 18/1/17 at 06:01 PM Reply With Quote
The cap on the radiator needs to be a blanking car and not a pressure seal cap. This way you should then have a continuous flow of coolant from the small bore pipe back to the header tank. Don't think about the head gasket until you have completely eliminated cooling system issues. I convinced my self I had a blown head gasket on my marlin when It was infacy my header tank set up and a massive airlock.
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Plunky

posted on 18/1/17 at 06:20 PM Reply With Quote
Just been out to the car to investigate further...
The cap on the rad is in fact a pressure cap! So I am hoping this is where the problem lies!
Next question is... is it easier to source a blanking cap for the rad or get a not pressure cap for the tank/new tank?

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r1_pete

posted on 18/1/17 at 06:57 PM Reply With Quote
Look for an austin / morris 1300 plain cap, for the rad, they are only a few quid

AUSTIN,MORRIS,MG, WOLSELEY 1100,1300 ADO16 BL NEW OLD STOCK RADIATOR CAP 21H5934

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Plunky

posted on 18/1/17 at 07:00 PM Reply With Quote
Cheers!
I found this...
Fahler Polished Stainless Steel Radiator Rad Cap Expansion Tank Blanking Cap
assuming it is essentially the same thing!
I am guessing they are all a standard diameter?

quote:
Originally posted by r1_pete
Look for an austin / morris 1300 plain cap, for the rad, they are only a few quid

AUSTIN,MORRIS,MG, WOLSELEY 1100,1300 ADO16 BL NEW OLD STOCK RADIATOR CAP 21H5934

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r1_pete

posted on 18/1/17 at 07:31 PM Reply With Quote
Yep, that'll do you fine...
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