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Coolant Overflow


jonmathias

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Hi All

My car is a Sigma-engined 270, a year old, having had its first service back at the factory a few weeks ago.

Went out for a sedate drive yesterday (Mrs M was on board). All seemed fine, temp around 90deg. Was out for an hour or so. Got back and a few minutes later I noticed a small puddle of coolant under the front of the car. 

Just spent a while investigating...No evidence of any leaks from any hoses, but lots of splashes  around the expansion bottle. When the engine is cold, the level in the expansion bottle is fine, just above the min line, so I figure it can't have lost a huge amount yesterday.

I ran the engine up to temperature. There is a steady flow of coolant back into the expansion bottle while the engine is running (I'd estimate the flow to be about a teacup or two a minute), but gradually the expansion bottle fills up and eventually, after about 10 min of idling, overflows through the filler cap. I switch off, and as the engine cools, the level in the bottle drops - it's 20 min later now, and the level is now almost back to where we started.

Could there just be too much coolant in the system, or maybe there's a blockage somewhere causing too much to flow back to the expansion bottle? Any idea how much should be flowing back to the bottle during normal running?

cheers

Jon

 

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Thanks Jonathan

Have now run the engine for another half hour, with the heater valve open, but no sign of any change, and the pressure cap looks fine to me.

Being relatively new to the car, I'm not sure whether it's normal to have a constant flow of coolant back to the reservoir in the Sigma engine?

For the time being, I've just taken out about 1/2 litre, which means the level is well below 'min' when cold, but avoids overflowing when hot.

I'm worried that if there is a blockage somewhere in the system causing the flow back to the expansion reservoir, I'm going to get localised overheating and block/head damage...

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Yes, both the thermostat and the fan operate at the right temperatures - the engine is not overheating, but the expansion tank is overflowing.

I have a new theory that I briefly tested the other night after work and will investigate more fully this w/e: although the pressure cap looks OK, I have a feeling it's not seating properly and allowing pressure to escape. Insufficient back pressure in the overflow is allowing too much fluid to accumulate there and eventually it fills up.

So I'm going to either seat the cap better or somehow temporarily seal the filler hole with something else to see if it prevents the level rising too much....maybe I need a new cap or even the whole tank.

What I'm still unclear about is whether I should normally expect there to be a constant flow into the tank through the top (thinner) hose? I was a bit surprised to see that, but it may be perfectly normal.

Many thanks for all the help so far :-)

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... although the pressure cap looks OK, I have a feeling it's not seating properly and allowing pressure to escape. Insufficient back pressure in the overflow is allowing too much fluid to accumulate there and eventually it fills up.

As in #4 I'm suspicious of the cap. Buy or borrow a good one to check?

Jonathan

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Just to wrap this thread up - it looks like is was a problem with the seating of the pressure cap. Having cleaned everything up and made sure it tightens down properly, it's now making a good seal and containing the level of fluid in the overflow tank.

Thanks to all for your input :-)

Jon

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  • 5 weeks later...

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