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  • [Non Corsa] Overheating issue

    On the Audi - symptoms are at idle the coolant temperature keeps increasing (according to the gauge on the instrument panel). The bottom radiator hose is cold and doesn't seem to have much pressure to it and, although not properly checked, the heaters are cool (checked with engine off 5-10 minutes after it was up to temperature). Coolant in the expansion tank heats up and when the lid is slowly released, coolant flows into the tank from the 'Highest point in system' hose on the diagram below. Any ideas? Taurus I'm looking at you here.

    Thermostat? Air lock? Cooling fan not working properly? Blocked radiator? CTS?

    Coolant was recently replaced but I cannot be certain as to whether the issue existed before this or not.

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  • #2
    Am I right guessing you're not actually driving this at the moment, so it's just idling? It is usual for the gauge to rise when idling, but I guess yours is rising to the point of reading too hot.

    If the coolant was changed recently then I'd start with making sure there isn't an airlock. If the gauge is showing hot and the lower rad hose is cold and soft then it suggests lack of flow, as does the heaters being cool.

    Have you tried bleeding the system? Sometimes it helps to bleed the cooling system with the car at an angle.

    The cooling fan ought to be checkable by bridging the thermoswitch.

    The CTS will be to drive the ECU fuel/air ratio so if it was dud it wouldn't cause the problem you're describing.

    If the radiator was blocked it would just get hot and then the cooling fan would kick in. You don't say the fan is running so I'm guessing the gauge is showing hot but the fan isn't running - which suggests lack of flow.

    It could of course be a stuck thermostat or a failed water pump, but check for an air lock first. It's more likely if the coolant has recently been changed. Even these self-bleeding systems can be a pain to refill without getting air into them somewhere, and if the air shifts to a point where it blocks the flow you get overheating pretty quickly.
    1972 Viva restoration thread - http://www.thecorsa.co.uk/projects-b....html#post1534

    Comment


    • #3
      Am I right guessing you're not actually driving this at the moment, so it's just idling? It is usual for the gauge to rise when idling, but I guess yours is rising to the point of reading too hot.

      Correct, it is not being driven at the moment, only idling. Temperature should sit steady at 90 but creeps up towards 105-110.

      If the coolant was changed recently then I'd start with making sure there isn't an airlock. If the gauge is showing hot and the lower rad hose is cold and soft then it suggests lack of flow, as does the heaters being cool.

      Have you tried bleeding the system? Sometimes it helps to bleed the cooling system with the car at an angle.

      No, I haven’t attempted bleeding it yet. It’s my first port of call I just haven’t had the chance to try it.

      The cooling fan ought to be checkable by bridging the thermoswitch.

      The main fan is a viscous one that runs directly off the engine so there is no thermoswitch to bridge. It’s meant to speed up once a certain temperature is reached, but that didn’t appear to happen. There is a secondary fan for the aircon that doesn’t work, I’ve a feeling that’s also meant to kick in at a certain temperature to help with cooling. This one should have a bridgeable switch, access is tight though and requires a bit more investigation on my part.

      The CTS will be to drive the ECU fuel/air ratio so if it was dud it wouldn't cause the problem you're describing.

      If the radiator was blocked it would just get hot and then the cooling fan would kick in. You don't say the fan is running so I'm guessing the gauge is showing hot but the fan isn't running - which suggests lack of flow.

      It could of course be a stuck thermostat or a failed water pump, but check for an air lock first. It's more likely if the coolant has recently been changed. Even these self-bleeding systems can be a pain to refill without getting air into them somewhere, and if the air shifts to a point where it blocks the flow you get overheating pretty quickly.

      I really hope it isn’t the thermostat or water pump. Even the thermostat is a cam belt job for this engine. Looking at the flow diagram, I can’t see it being the thermostat seeing as hot coolant is returning to the expansion tank, suggesting it is getting through the engine (the thermostat is located at the junction between the thin coolant pipe along the bottom of the radiator and the cold bottom radiator hose – right of the word ‘bypass’). There isn’t an obvious radiator cap that I can see so I’ll look to see if there’s a bleed screw on it. If there’s no flow through the radiator then that would explain the cold hose but hot coolant returning to the expansion tank as the radiator would essentially be bypassed.

      When I drained the coolant it’s unlikely to have drained from the engine, but it definitely would have emptied the radiator.
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      • #4
        OK - that makes sense. In which case try bleeding the system, it is likely the block would partially drain when you dropped the coolant and partially drained systems tend to airlock the worst.
        1972 Viva restoration thread - http://www.thecorsa.co.uk/projects-b....html#post1534

        Comment


        • #5
          Originally posted by Taurus View Post
          OK - that makes sense. In which case try bleeding the system, it is likely the block would partially drain when you dropped the coolant and partially drained systems tend to airlock the worst.
          Doesn't seem to be anywhere on the radiator I can bleed it so I'll have to use the heater bleeding port by the firewall. If an air lock exists in the radiator hopefully it will get forced round to the back of the engine to escape.

          Didn't have a chance to try it last night as the X-Trail has also decided to stop working. 1 car out 4 that can be used at the moment. It never rains but it pours...
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          • #6
            That bleeding point looks to be at the highest point of the system so it should bleed the entire system.
            1972 Viva restoration thread - http://www.thecorsa.co.uk/projects-b....html#post1534

            Comment


            • #7
              Yeah it's pretty high. From what I've been reading online no one seems to bother with the other bleed port as it's lower and the screw can be very fragile. The heater matrix bleed port is just a small hole in the hose - all you have to do is loosen the hose clip and pull the hose back so that the hole is clear of the pipe.

              I'll report back once I've had a go.
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              • #8
                Bled the system. Started by freeing up the heater hose bleed hole with engine off and I blew into the expansion tank. That definitely cleared some air. Then let the engine run until coolant came out of the hole. Pushed the hose back on and tightened the jubilee clip.

                Carried on letting the car idle and the temp crept up again. The viscous fan didn't speed up again, but on the plus side this means revving the engine and holding it at about 2k means the fan speeds up enough to quickly bring the temp back down lol. Bottom rad hose eventually got hot and the heaters blew hot too.

                So air lock sorted, thermostat and water pump are working, viscous fan doesn't automatically speed up and additional electric fan doesn't kick in.

                Powered the electric fan directly from the battery and it span, so the motor is fine. If neither the viscous fan or electric fan are initiating with temp then my money is on a dodgy sensor.

                As there is a budget and knowing I can cool the engine with revs, I'm tempted to leave the responsible sensor alone and just wire the electric fan to the battery permanently. It is going to be August in Europe after all.
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                Comment


                • #9
                  If it's just a temp sensor and it's not expensive it might be worth a try if nothing else needs replaced which eats into the budget.

                  Comment


                  • #10
                    Yeah it's definitely worth looking in to how much it may cost but it's good to know I have a bodge to fall back on if needed.
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                    • #11
                      Viscous fans work differently, you won't see them speed up directly proportional to the temp gauge. Revving will appear make the fan work harder but you are also generating a lot more heat of course.

                      Personally, if there's a secondary fan I'd just make a override switch arrangement. You can then flip it on if you get stuck in traffic - on the move you're very unlikely to need it.
                      1972 Viva restoration thread - http://www.thecorsa.co.uk/projects-b....html#post1534

                      Comment


                      • #12
                        Yeah I realised the mistake after I'd written it with referring to the viscous fan responding to a sensor. But the point remains that with age viscous fans lose their effectiveness and this one seems to be no different. It should speed up around 100 but the temp has gone to 105-110 with no response. Of course this is all assuming the dash gauge is accurate.

                        I also expected revving not to work due to the increase in heat generated, but it was surprising how effective it was and how quick the coolant temperature responded (according to the dash gauge).

                        I have an old 3 pin switch kicking about from the fog light in the MX5 that I could probably use for the secondary fan.
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                        [URL="https://www.thecorsa.co.uk/forum/general-discussion/car-chat/projects-builds/225-atlantis-blue-5-door"][B][COLOR="#0000cd"]Corsa B Atlantis Blue[/COLOR][/B][/URL]
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                        • #13
                          If I were to put in a switch, using this simple circuit pinched from the internet, where would the fuse go (20a-30a)? And what size wire would I need?

                          I'm not the best with electrics and never know how to decide what thickness wire is appropriate.

                          Remember budget is key so I'd like to avoid using a relay, but obviously I still need it to be safe!

                          [URL="https://www.thecorsa.co.uk/forum/classified-ads/parts-for-sale/1043-big-clear-out-exhaust-suspension-etc"][B][COLOR="#0000CD"]Big clear out of parts[/COLOR][/B][/URL]
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                          [URL="https://www.thecorsa.co.uk/forum/general-discussion/car-chat/projects-builds/225-atlantis-blue-5-door"][B][COLOR="#0000cd"]Corsa B Atlantis Blue[/COLOR][/B][/URL]
                          [URL="https://www.thecorsa.co.uk/forum/general-discussion/car-chat/projects-builds/1301-1993-mazda-eunos-roadster"][B][COLOR="#006400"]Mazda Eunos V-Spec[/COLOR][/B][/URL]

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                          • #14
                            Does it not already have a thermoswtich for the fan? If so then all you need to do is to bridge the thermoswtich with some 5amp wire. The load will go through the existing relay. Same trick as lots people do on the Corsair B.

                            Re the viscous fan, revving will also pump the coolant faster. If you are running it at idle with the bonnet open the viscous coupling may not be getting hot enough to activate it. You could see if it can be drilled and locked off, it won't affect fuel consumption that much but it will ensure the fan is turning with the engine.
                            1972 Viva restoration thread - http://www.thecorsa.co.uk/projects-b....html#post1534

                            Comment


                            • #15
                              I assume it has a thermoswitch but for the life of me I cannot find it. There's a connection part way along the fan wires that you can disconnect - this is what I used when I manually wired it to the battery to test it last night, so I was planning on fashioning a circuit using that.

                              Problem with this car is that there are so many variations and different engines that pinpointing the correct information online is really difficult.
                              [URL="https://www.thecorsa.co.uk/forum/classified-ads/parts-for-sale/1043-big-clear-out-exhaust-suspension-etc"][B][COLOR="#0000CD"]Big clear out of parts[/COLOR][/B][/URL]
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                              [URL="https://www.thecorsa.co.uk/forum/general-discussion/car-chat/projects-builds/225-atlantis-blue-5-door"][B][COLOR="#0000cd"]Corsa B Atlantis Blue[/COLOR][/B][/URL]
                              [URL="https://www.thecorsa.co.uk/forum/general-discussion/car-chat/projects-builds/1301-1993-mazda-eunos-roadster"][B][COLOR="#006400"]Mazda Eunos V-Spec[/COLOR][/B][/URL]

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