Dave pb Posted October 5, 2021 Report Share Posted October 5, 2021 Hello I have a coolant problem in that the overflow bottle is getting filled up, but is not returning once the engine cool down. I'm guessing first stop is the radiator cap (its been on since I bought the car 16 years ago), perhaps the seal is leaking. Any other ideas? Dave ==== Link to comment Share on other sites More sharing options...
johny Posted October 5, 2021 Report Share Posted October 5, 2021 Hi, can be a bit of a connundrum this! First is the actual overflow pipe in good condition, airtight including where it fits on the rad filler neck and always immersed in coolant in the overflow bottle? In use it should ALWAYS be full of liquid and a transparent pipe is useful for verifying this... Youre right to think the cap top seal could be leaking but also Ive suffered with leaks elsewhere in the system. Typically hoses leak where they clamp onto fittings and dont seem to lose coolant but do allow air to be sucked in on cool down. As a last resort, with the system cold, you can connect a hand pump with gauge to the radiator overflow pipe and pressurise so that you can look for leaks and/or pressure drop. Link to comment Share on other sites More sharing options...
johny Posted October 5, 2021 Report Share Posted October 5, 2021 Just thought, if using the pump method dont over pressurise the system as obviously the cap wont be able to lift to protect it.... Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 5, 2021 Report Share Posted October 5, 2021 i would go for a new cap the upper cap seal is a pretty basic bit of card or rubber its not very special also the filler neck any dents or distortion will not seat the seal you could cut a new seal from a cornflake packet to try before you buy do make sure the new cap is the correct depth to make sure the pressure seal locates on the inner filler neck seating there are two depths of caps available Pete Link to comment Share on other sites More sharing options...
daverclasper Posted October 5, 2021 Report Share Posted October 5, 2021 1 hour ago, Pete Lewis said: also the filler neck any dents or distortion will not seat the seal That was my main issue (also the overflow hose maybe leaking air at filler neck), the top of filler neck not quite flat, used some fine ish wet and dry on a sanding block. Link to comment Share on other sites More sharing options...
Ian Foster Posted October 6, 2021 Report Share Posted October 6, 2021 Dave I had exactly the same problem traced to distortion of the filler neck as Jonny and Pete have suggested. A quick pass with some fine wet and dry of a flat block will show where the problem is. Worked a treat for me! Ian Link to comment Share on other sites More sharing options...
Dave pb Posted October 6, 2021 Author Report Share Posted October 6, 2021 Thanks everyone. I think I'll start with the cornflakes washer, and a bit of wet and dry. Rooting around yesterday I found a a suspect hose junction - not conclusive but currently in the line-up of culprits. Dave ==== Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 6, 2021 Report Share Posted October 6, 2021 its all down to years of appendage's being used to refill top up and add antifreeze the rim gets a bashing cornflakes packets always useful to have handy Pete Link to comment Share on other sites More sharing options...
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