rusty_wingnut Posted April 10 Share Posted April 10 All, I have an odd issue, that I am not sure is even an issue, it all started a few weeks back chugging up the hill out of Farnham towards Guildford, accelerating up to 60mmph, I noticed the temp gauge climbing, so I backed off, and although it was running a little hotter than usual it wasn't boiling. I had removed the engine fan the night before as I was replacing a leaky power steering pump, and hadn't refitted it - what with it being spring and hardly warm! I got back via the A3/M25 and although running hot it hadn't boiled (maintaining a steady 55mph) Now since being back I cannot seem to maintain a full air free thermostat housing despite bleeding twice and filling through the bleed plugs. This may/may not be an issue but I am sure my old 300tdis would bleed up and remain full wether hot or cold. With the engine running and it bleeds no issue, tighten it back down, drive, let it cool and then open the plug, coolant has only reached as high as the bleed valve on the thermostat. Since being back I've done a few checks- Thermostat opened although not fully, confirmed in the same pan with two others - the one that opened the most was refitted. (assumed faulty thermostat) Water pump confirmed as fins turning and no leaks. No visible leaks at heater box. Swapped seal on thermostat bleed plug, incase air being drawn in. Changed Y piece, old one checked and all clear Swapped for known good expansion cap Checked expansion hose fitting on thermostat housing is clear There are no bubbles in the header tank when hot/cold/revved for the head gasket doom mongers No leaks around P gasket Am I worrying about nothing? I will do a long journey later in the week on the motorway. Quote Link to comment Share on other sites More sharing options...
rusty_wingnut Posted April 10 Author Share Posted April 10 Could someone with a 300tdi confirm that the thermostat housing isn't full of coolant when cold? Quote Link to comment Share on other sites More sharing options...
fmmv Posted April 10 Share Posted April 10 28 minutes ago, rusty_wingnut said: Could someone with a 300tdi confirm that the thermostat housing isn't full of coolant when cold? Mine certainly isn't. If you take the plug out there is always some air, by the time the plug is out there is anyway, can't see through the plug so it may have been full. If the heater is working there probably isn't an airlock, that seems on mine to be the first thing to show an airlock. 1 Quote Link to comment Share on other sites More sharing options...
jwhitton Posted yesterday at 03:06 AM Share Posted yesterday at 03:06 AM Did you solve this? Interested in what it was! Quote Link to comment Share on other sites More sharing options...
Snagger Posted yesterday at 06:52 AM Share Posted yesterday at 06:52 AM On 4/10/2024 at 4:56 PM, rusty_wingnut said: Could someone with a 300tdi confirm that the thermostat housing isn't full of coolant when cold? I think it should be full of coolant. I had similar problems with my RRC 300. It was the Y-piece in the expansion hoses from thermostat housing and rad top to the tank being blocked up. I cleaned it with a length of welding wire. Be very careful- the plastic becomes very brittle with age and heat. Quote Link to comment Share on other sites More sharing options...
rusty_wingnut Posted yesterday at 07:10 AM Author Share Posted yesterday at 07:10 AM Well, not sure it was resolved as such, I fitted the new radiator cap, and Y piece. There's no loss of coolant, so I refitted the fan and left it. Done a couple of long runs and it seems OK, honestly I am not sure what happened. I even started to wonder if the sender was breaking down in some way. Long term I will probably fit a proper temperature gauge. Quote Link to comment Share on other sites More sharing options...
Snagger Posted 21 hours ago Share Posted 21 hours ago Fingers crossed. External leaks are usually fairly easy to identify, but cracks in the head or a failing head gasket are often impossible to diagnose without removing the head. Pinhole leaks in the system can retain the coolant but might suck air in as the engine cools down, which can be a swine to find. As long as your coolant is staying at the same level once cooled down, then you don’t have any immediate problems, but it’s far from ideal to have false indications and an inefficient heater in winter. Quote Link to comment Share on other sites More sharing options...
Ed Poore Posted 20 hours ago Share Posted 20 hours ago Recently recovering @Bowie69 when his brakes failed mine got hot. Put almost 10l of water in but nothing leaking. Thinking back it had been closing water very very slowly. When I called in with @TSD checked the levels and they were low and for the time noticed it was damp around a load of the coolant pipes, but only just. After 30 years the rubber hoses are finally beginning to give up and weep slightly through cracks. It was almost sheer fluke we'd spotted it as normally the engine bay hasn't been that dry because of road splatter. Quote Link to comment Share on other sites More sharing options...
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