jonmathias Posted September 15, 2019 Share Posted September 15, 2019 Hi AllMy 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?cheersJon Link to comment Share on other sites More sharing options...
SM25T Posted September 15, 2019 Share Posted September 15, 2019 What was done during the service. If they replaced the coolant or any part of the circuit, there could be an airlock in there, preventing circulation. Maybe you opened the heater valve yesterday and exposed the airlock trapped in there ? Link to comment Share on other sites More sharing options...
jonmathias Posted September 15, 2019 Author Share Posted September 15, 2019 Service sheet just says check level and top up if needed. I did reach under the dash to make sure the heater was off, but didn't open the valve... Link to comment Share on other sites More sharing options...
Jonathan Kay Posted September 15, 2019 Share Posted September 15, 2019 I'd start with the simple stuff:Rebleed, and top up if necessary. Heater circuit open at some point. Does the pressure cap look OK, and does it snug up nicely?Jonathan Link to comment Share on other sites More sharing options...
jonmathias Posted September 16, 2019 Author Share Posted September 16, 2019 Thanks JonathanHave 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... Link to comment Share on other sites More sharing options...
SM25T Posted September 16, 2019 Share Posted September 16, 2019 Feel all the hoses when it is warmed up and thermostat is open. Are any still cold ? This would show an airlock. Does the fan come on as normal ... at 92C (ish) ? Link to comment Share on other sites More sharing options...
pgm Posted September 16, 2019 Share Posted September 16, 2019 Have had the thermostat fail on a sigma engine but that resulted in a overheating situation. Presume the fan is cutting in correctly? Link to comment Share on other sites More sharing options...
jonmathias Posted September 19, 2019 Author Share Posted September 19, 2019 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 :-) Link to comment Share on other sites More sharing options...
Tazio Posted September 19, 2019 Share Posted September 19, 2019 I have a VX, and water cycles through the small hose into the expansion tank. The hose has a jiggle valve restrictor to slow flow down. Link to comment Share on other sites More sharing options...
ScottR400D Posted September 19, 2019 Share Posted September 19, 2019 I have a Duratec and as I recall there is a flow into the tank. I think the cap is a good call; they’re not the most reliable but cheap to replace. Link to comment Share on other sites More sharing options...
7 wonders of the world Posted September 19, 2019 Share Posted September 19, 2019 check that the expansion bottle spout over which the 8mm hose fits inside there should be a metal restrictor so as to only allow a bleed into the tank not a full flow... seen a couple with no restrictor in them. Link to comment Share on other sites More sharing options...
Jonathan Kay Posted September 19, 2019 Share Posted September 19, 2019 ... 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 Link to comment Share on other sites More sharing options...
jonmathias Posted September 22, 2019 Author Share Posted September 22, 2019 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 Link to comment Share on other sites More sharing options...
Copsnewick Posted October 21, 2019 Share Posted October 21, 2019 I have a 310r and on the first cold day out my heater didn’t work, fan ok blows cold air only despite car reaching temp around 60 . Could this be a problem with the pressure cap Link to comment Share on other sites More sharing options...
Jonathan Kay Posted October 21, 2019 Share Posted October 21, 2019 I'd start by topping up and bleeding.Then check that the heater valve opens fully.Then get it warmed up and feel which hoses are hot.Jonathan Link to comment Share on other sites More sharing options...
SM25T Posted October 21, 2019 Share Posted October 21, 2019 Did you pull out the heater control knob to turn it on ?? Link to comment Share on other sites More sharing options...
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