Engine coolant airlock thread

[Logan Colbeck]

Help!

I need to access a thread I saw some time ago on eliminating an airlock in my Duratec cooling circuit. Anyone recall this or can offer comment?

Many thanks in advance,

Logan.

[mossy7]

Try this in your browser

site:lotus7.club duratec air lock

 

Andy

[John Vine]

Have you tried searching on "Duratec AND airlock AND cool"?  It produces a few possible hits.

(But mossy7's Google search is much better!)

JV

[dave_h34]

I've not experienced problems with mine as such but have noticed the coolant level varies a bit between max and min after any given run out. That led me to take a look at the radiator bleed and there was a good amount of air trapped in there. I've topped it up directly but as yet haven't had a run out to assess the result. Reading around the subject it seems the heater can cause air trapping so I've bought, but have yet to fit, one of these: http://www.ebay.co.uk/itm/302200021471 Seems like a good idea and very simple. When the weather picks up I'll be able to do more testing.

[Jim 123]

Here's my theory on Duratec/Sigma air locks to be shot down in flames......

Having tried to bleed air from a valve (as Dave suggested) fitted at the heater, and also bleed the top of the radiator as well, the coolant level continues to fluctuate after driving.. 

When the engine runs, you can see there is a constant flow into the Coolant Reservoir from it's top inlet pipe.  Because the inlet pipe is so high above the main body of fluid in the Coolant Reservoir, the "returning" coolant gets aerated as it drops into the main body of liquid in the Coolant Reservoir.

The "gassy" coolant then gets immediately drawn from the Coolant Reservoir back into the engine cooling circuit. Air then builds up at the high points in the circuit, and you note the Coolant Level creeps up.  As air builds in the system, the Coolant level rises above "Max."  With a higher Coolant Level in the Reservoir, there is reduced tendency for aeration from the inlet pipe, and things start to balance out, albeit with a high Coolant Level reading.

If the return pipe was placed below the surface of the main body of fluid in the Coolant Reservoir, the system would not gas up.

[7 wonders of the world]

No,

The bleed pipe is set to flow the coolant around the expansion tank in order to de aerate it, were it under the coolant level you would introduce any air present into the coolant.

 

 

[ScottR400D]

This intrigues me. I've never been aware of any coolant level/air trap issues with my Duratec and never gone to any special lengths when filling just bled at the rad and heater. 

[Jonathan Kay]

Maybe the problem is as sporadic in Duratec engines as it is in K series engines...

I hope that application of the known solutions (!) is as effective.

Jonathan

[Jim 123]

Re 7 Wonders comments, as I said in my earlier post, I willingly stand to be shot down. 

I agree with 7 W's observation about the intention of the bleed pipe, but I suspect that on the later Caterhams we may have an issue because of the unique location of the Coolant Reservoir. 

Normally, in say a range Rover, these bottles are located under the hood at the highest point in the cooling system, and the "bleed" does what is should do.  Because of the Coolant Bottle's low position in the Caterham, the bleed pipe does appear to cycle a larger-than-conventional volume of coolant back into the bottle.  If you observe this, you can see the coolant flow  is greater than a normal bleed pipe function; especailly before the Thermostat starts to open.  When coolant is flowing back into the bottle via the bleed pipe it p*sses in, and coolant from the bleed pipe doesn't flow around the bottle (to avoid gassing) as per the design intent.

The other thing that I found a problem with, is that the Max and Min Level markings on the Coolant Bottle face to the front of the car, and can not be observed without popping the nose cone off.  I'd suspect a number of owners may not pick up that the coolant level has risen above Max because they can't actually see the Max Level marking.  On my car the Max Level indicator is front-facing and it is below the moulded center band around the Coolant Bottle.  After a coolant fill up to the Max marking, followed by some driving, the coolant level tends to rise above moulded center band, but if you can't see the Max Level line on the Coolant Bottle you don't pick up that the level has risen.

[7 wonders of the world]

It's worth checking your bottle, the inlet for the bleed is usually restricted with a metal insert similar to a roll pin in the plastic neck, this takes the ID down to 3-4mm if this is missing the ID is circa 8mm.

 

[slap_ed]

I've just drained and re-filled my Duratec cooling system due to changing the thermostat. From the system being empty it took 6.8 litres. I filled it slowly with the top radiator bleed bolt out and the plastic T-piece unscrewed off.

After pouring in about 6 litres and the coolant level in the expansion bottle being at max I fitted the expansion cap. I then gently squeezed the top hose until the coolant came out of the radiator bleed bolt hole and quickly screwed the bolt back in. I then poured the remaining 0.8 litres in through the plastic tee until this filled to the top allowing quite a few bubble to slowly escape out. When these stopped I screwed the top on.

Went for a test run and all was fine, so no problems from my point of view. Didn't have to top up either.

This doesn't help you but it's another thumbs-up for filling a Duratec without problems.

It's not something silly as the radiator cap that's not allowing the system to pressurise properly therefore allowing the water to boil if it gets to 100 deg which may introduce air into the system and for the level to rise. I know my Duratec fan doesn't come on until it gets to 98 deg so things can run quite hot.