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2nd Expansion tank above LHD wheel

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That’s the actual expansion tank. The header tank in the engine bay is more of just a central point really for the turbo return and where the pipes for the expansion tank go in and out. Without an expansion tank you’ll blow hoses off unless you put the pressure cap there.

It is meant to be about 1/4 full. Coolant expands into it then as it contracts, it’s pushed back into the other metal tank.

Doesnt seem to do that on mine though, so that expansion tank is always empty, and the header tank usually about 3/4 full. I’ve actually just fitted a new pressure cap today as it happens to see if that fixes it.

-edit- it works! The new pressure cap has fixed mine. Went for a run earlier. Now it’s cooled down I’ve checked, and the header tank is full. And the expansion tank is the correct 1/4 full. :)

Edited by Glyn Harper
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Interesting, thanks!
I think mine stays more or less empty too. Were did you source your pressure cap? Any cross reference?

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I just bought a new one from SJ Sportscars in the UK. I think it’s not been sealing properly for years but all looks good now.

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Giniw - with the single white plastic tank on the S4s, the pressure cap (15lbs) on the header tank should have a thin rubber gasket at the top to seal off the very top of header tank filler. This allows it to dump coolant into the expansion tank via the top connection when the pressure overcomes the cap spring. When it cools, it contracts, sucking coolant back into the header tank. The header tank should always be full.

The coolant level in the expansion tank should be about 30% when cold (I think there’s an arrow indicating the level). That said, the tank is identical to one from a Morris Marina, so I don’t think the arrow level is critical! The main thing is that you don’t allow it to become empty, or the system can drag air back in. If it’s working properly, the expansion tank coolant level should rise and fall with engine temperature.

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The coolant lasts longer and is less likely to cause corrosion problems when contact with air is avoided as much as possible. That's why the header tank is kept full and the expansion tank does the job of accepting and returning coolant to the system.

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Giniw, the cooling system needs to be air-free for anti-corrosion reasons, but mainly to prevent air pockets from forming, which can create hot-spots. Wherever possible, the coolant system integrity should be maintained by not releasing the caps, which allows free air in. The S4s system is effectively 'sealed', and shouldn't need any topping up unless there are leaks. Coolant concentration is important too, and should not be allowed to fall below the manufacturer's recommended level.

I once experienced problems on eight 16 litre Volvo engines that were suffering pin-holed cylinder liners. The upshot was that the lower end of the liners, being supported with rubber O-rings, would move with each firing. When the liner moved away from the coolant on the firing stoke it caused cavitation, which ate its way into the liner. This manifested itself as what looked like a row of minute holes through the liner, and coolant would then weep into the engine crankcase. The only solution then was a very expensive, complete rebuild.

It turned out the previous incumbent had been using 'aftermarket' coolant at 30% instead of 50%, using lower pressure caps than he should have done, and the coolant levels were being regularly checked by removing the pressure cap, allowing free air into the system. After increasing the coolant concentration, fitting higher rated pressure cap, and fitting a remote expansion tank in which the coolant level could be seen without pressure cap removal, the problems were cured. There are many examples of this kind of thing on the web. Not saying the 910 suffers from it, just worth making sure the system is compliant with the recommendations.

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Thanks a lot. Yesterday I was in the boot to address a few things (:D) and I had a look at the caps. They look OK but  I am a bit surprised the pressure cap is on the header tank: how can the coolant go back to the main circuitry though the closed pressure cap when it's in the expansion tank?! (the 15 PSI pressure cap is #137, and #173 is just a flat cap without spring)

PS: I am currently installing a new aluminium pipe which was leaking a bit and that was corroded ... (item #3, was corroded at the bottom near the rubber pipe which was leaking a bit, probably a bit loose)

Does it sound normal that an aluminium pipe can corrode because of the coolant? It's strange because it's not corroded in the inside, just the outside where it was in contact with the rubber?! Coolant in contact with air would actually be corrosive?!

coolant.png

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On the diagram you posted, ONLY the cap on the expansion tank (173) is a pressure cap.

The cap on the header tank (111) just has a rubber in the top to seal the actual bottle. It has no spring in there and does not seal within the tank, just at the surface.

The chargecooler cap (112) is a pressure cap.. but I think a different pressure rating to 173.

Otherwise, as you say, fluid will not be able to flow back into the header tank from the expansion tank.

I’ve heard before people have fitted the caps the wrong way around so you’re not the only person to do that.. if indeed you have :)

I don’t have the bottle you must have, so I don’t have cap 137. But if I understand correctly the difference in the later car, then 137 should should be a flat cap without a spring. Is that the bottle that was when the chargecooler and engine coolant were together with the same expansion tank? I’m glad mine are separate.

I took mine for a run tonight and checked the expansion tank. It increases the fluid level by about 25mm when the engine is hot, then drops back down to the marker line as it cools down.

About your pipe.. Are you sure the pipe is corroded so badly you need to change? Can it be sanded back to a smooth finish that will seal again?

when aluminium is in contact with water and air and then it moves or vibrates, I believe it produces an electric charge which causes corrosion.. so yes, it’s possible. It’s the same reason allow wheels go powdery and you get a white rust tracking under the lacquer.

If you are fitting a new pipe, anodising it will help.

Edited by Glyn Harper

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My caps are configured the same as Giniw. The pressure cap is on the header and a flat cap on the expansion. The pressure one is 2 way. Any others like to check and comment?

The header tank (ball shape) was originally fitted to Peugeot 205GTI. There it had no expansion tank so didn't stay full to the brim like it does on our cars because of the expansion tank.

I also had problems with pipe #3. There was a bracket at the bottom bolted to the chassis and clamped to that pipe. With the rocking of the engine that bracket eventually broke and the movement did cause leakage problems. I made another stronger bracket which I rubber mounted to the chassis. Very similar to how exhaust pipes can be supported with rubber mounted brackets. I also had to repair the bleeder pipe "L" bend on the top of pipe #3 to fix a leak there.

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There are two different arrangements shown in the parts diagram, the S4 and S4s use tank number 135, not the earlier twin tanks.

On the S4s, 137 is the header tank pressure cap, 173 is the expansion tank blanking cap. The pressure cap has a small valve in it that allows coolant back in from the expansion tank as the system cools.

Corrosion is common on alloy pipes under the rubber connections, you’re not experiencing anything new!

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15 hours ago, Glyn Harper said:

Are you sure the pipe is corroded so badly you need to change?

It was leaking, so I removed the pipe to clean it indeed: the corrosion holes became through holes just when I brushed them, so ... yes it needed to be replaced ^^ (I tried to solder the holes, I succeeded with the first but for the second series of craters the aluminium rod didn't want to melt properly, I suppose I couln't heat it enough. So I ordered a new one.

15 hours ago, Glyn Harper said:

when aluminium is in contact with water and air and then it moves or vibrates, I believe it produces an electric charge which causes corrosion.. so yes, it’s possible. It’s the same reason allow wheels go powdery and you get a white rust tracking under the lacquer.

Interesting, I had never heard about that (nor the wheels issue)

15 hours ago, Glyn Harper said:

If you are fitting a new pipe, anodising it will help.

Shucks, too late. Is it easily doable at home? I should have a look =)

 

5 hours ago, Chillidoggy said:

The pressure cap has a small valve in it that allows coolant back in from the expansion tank as the system cools.

That makes sense, I will check that, thanks!

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You can get home anodising kits. I don't know how easy they are to use though. :) There are youtube videos on the subject.

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Thanks I will have a look. (Maybe I should make a pipe in solid gold to prevent corrosion!)

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1 hour ago, Giniw said:

Thanks I will have a look. (Maybe I should make a pipe in solid gold to prevent corrosion!)

No, in Titanium. ;)

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Mmm, yes, milled in a big bloc of titanium, that would be nice too! :D

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Just picking up on the comments above - my X180 has the header and expansion tank caps as stated above with just the pressure cap on the header reservoir. 

My car runs at a very constant 80-82 degrees moving or even when idling in traffic. Once of twice (every couple of hundred miles) I've added say, 1/4 quarter pint of anti freeze to the header where the level has dropped below the recommended (about half filled) marker.

Today with the car cold and having covered 2-300 miles since the last top up, I checked the header tank and it needed a little top up again. However, I also checked the expansion reservoir as I was replacing the jubilee clips and that tank was very low. Rightly or wrongly (I've half recall posts about not topping up the expansion tank) I topped it up anyway with about 3/4 pint of coolant.

Is this normal, or, could I have an air block somewhere?

I seem to have a non-standard aluminium expansion tank fitted by the previous owner?

Pics

20180521_143152 - Edited.jpg

20180521_143214 - Edited.jpg

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P.S.

Blue or Pink antifreeze?

I've always thought blue for older cars, pink for newer and not really sure why?

If the ready mixed stuff says suitable for all cars winter antifreeze and summer coolant it's okay?

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Blue it is then, and is it normal that the expansion tank could be just 1/3 full? 

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Just as long as there’s enough in the tank for the system to suck back in when it cools. I reckon anywhere between 30 - 50% when it’s cold should suffice.

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Mine now seems to stay around 30% when cold, too.

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On 21/05/2018 at 18:22, DaKa said:

P.S.

Blue or Pink antifreeze?

I've always thought blue for older cars, pink for newer and not really sure why?

If the ready mixed stuff says suitable for all cars winter antifreeze and summer coolant it's okay?

I’m running with pink, say’s it’s good for aluminium engines, is this correct ?

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The Organic Acid Technology coolant should apparently be avoided for old engines, but it's not very clear.

It looks like OAT coolant can be used in the Elise; on the other hand, as for the Elan M100 Lotus is not sure as they have not tested it at the time so they couldn't recommend it.

As for the Esprit maybe Lotus tested it too since it was sold at the same time than the Elise ... I am not sure which email we should use to contact them though?

https://www.youtube.com/watch?v=yAbfTtMKWOU

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