Hi All,
My disco seems to have developed a tendency to try and over heat but not all the time...
Driving to work in the morning (Torbay to Mt Eden) everything is fine, but coming home is when I have the issue, as soon as I start up the harbour bridge the temp starts to climb (normally sits horizontal) the temp only goes as high at the top of the white and never in the red (would turn the engine off before then...) and when coming down the other side it starts to drop off and sits just a fraction above horizontal. The on the flat al the way home it's sits close to normal, then when I hit the next hill at Greville it climbs again...
Now on the way up the bridge my air con is on full cold at about half full speed, now if I turn the air con to full heat and full fan the temp will go down to normal instantly.
As I see it it could be four things...
Bad thermostat
Blocked rad
Bad viscus fan coupling
Blown headgasket
I know the viscus fan coupling works on heat but does anyone know at what temp should it be stiff? at normal temp the coupling is just the same and stone cold, if the engine is idling at normal temp I can stop the fan with my hand, does this sound right?
And I don't seem to be losing any coolant, the expansion tank is sitting at half way, and it's done this everyday this week
So from that can anyone hazard a guess where to start?
Cheers, Jason
1994 Discovery - Overheating
Re: 1994 Discovery - Overheating
Your Fan sounds fine if not it would heat up at lower speeds
Its sounds like its only when its under load it heats up.
Check thurmostat and water pump first and waterpump drive belt tension
Air con has nothing to do with engine cooling only adds load to engine when on however, when your air con is on cold
theres a air con cooling radiator in front of your engine radiator that heats up and adds extra heat to the front of your engine radiator it has 2 electric fans that help cool it which could explain the temp difference when on
So when your air con is on theres more heat to get rid of
Hope that helps and makes sense
Its sounds like its only when its under load it heats up.
Check thurmostat and water pump first and waterpump drive belt tension
Air con has nothing to do with engine cooling only adds load to engine when on however, when your air con is on cold
theres a air con cooling radiator in front of your engine radiator that heats up and adds extra heat to the front of your engine radiator it has 2 electric fans that help cool it which could explain the temp difference when on
So when your air con is on theres more heat to get rid of
Hope that helps and makes sense
Re: 1994 Discovery - Overheating
If your not loosing coolant then it shouldn't be head gaskets (YET) if it really is getting that hot on a daily basis then it will blow something major soon.
Run it till hot and then with the bonnet open rev the engine, if the viscous is working the breeze blown back will be impressive! Alternatively run till hot again, switch off and then firmly tape a fan blade to the fan shroud. Start the motor again - if the viscous is duff the tape will hold the fan still. If it rips free (try a few gently revs no more than 2K) then it's good. It's not an exact science but usually works.
If you are not getting belt squeal then the water pump is turning fine.
My best guess is either blocked radiator or more usually all the fins between the cores have fallen off!. As you have an AC rad and all the fan stuff in front and behind the radiator it is hard to see the condition with out removal.
Also make sure you use coolant not just water. All alloy motors like the Rover V8 really need it. Replace or test the thermostat while the radiator is out too.
Reason why it cools when the A/C is on and turned to hot is you are adding an extra radiator with the heater matrix being cooled and blowing hot air at you! and the two electric fans in front of the A/C rad are switched by a switch on the thermstat housing OR when the A/C is on.
Hope that all helps - good luck!
Run it till hot and then with the bonnet open rev the engine, if the viscous is working the breeze blown back will be impressive! Alternatively run till hot again, switch off and then firmly tape a fan blade to the fan shroud. Start the motor again - if the viscous is duff the tape will hold the fan still. If it rips free (try a few gently revs no more than 2K) then it's good. It's not an exact science but usually works.
If you are not getting belt squeal then the water pump is turning fine.
My best guess is either blocked radiator or more usually all the fins between the cores have fallen off!. As you have an AC rad and all the fan stuff in front and behind the radiator it is hard to see the condition with out removal.
Also make sure you use coolant not just water. All alloy motors like the Rover V8 really need it. Replace or test the thermostat while the radiator is out too.
Reason why it cools when the A/C is on and turned to hot is you are adding an extra radiator with the heater matrix being cooled and blowing hot air at you! and the two electric fans in front of the A/C rad are switched by a switch on the thermstat housing OR when the A/C is on.
Hope that all helps - good luck!
Re: 1994 Discovery - Overheating
Thanks for the replies guys.
I've pretty much proven over the last couple of weeks that it seems to be related quite strongly to the AC...
I've driven the same route each day and with the AC on it pushes the needle up to the top of the white of gauge (never past it) and drops quite quickly once you turn off the AC. I've even gone as far as driving over the harbour bridge with the AC on moving the needle up, pulling off and going back over the bridge with it off and the needle not moving.
So it sounds like the AC is loading the engine...
I've also confirmed the fan is working fine.
I did pickup a thermostat to fit this weekend if I get the chance, before I do that I am going to try one more thing which is taking the boat for a tow, if the cooling system is that bad then the extra load of the boat should quickly show the same effect as the AC is I would have thought.
I'm also very keen to seem how well it pulls the boat, to be honest I'm not that impressed with my cars performance fullstop, my old Terrano diesel seemed to have more power... but may be that beacuse it wasn't fulltime four wheel drive (anyone ever tried the disco minus the front propshaft..?)
I'll keep you posted
I've pretty much proven over the last couple of weeks that it seems to be related quite strongly to the AC...
I've driven the same route each day and with the AC on it pushes the needle up to the top of the white of gauge (never past it) and drops quite quickly once you turn off the AC. I've even gone as far as driving over the harbour bridge with the AC on moving the needle up, pulling off and going back over the bridge with it off and the needle not moving.
So it sounds like the AC is loading the engine...
I've also confirmed the fan is working fine.
I did pickup a thermostat to fit this weekend if I get the chance, before I do that I am going to try one more thing which is taking the boat for a tow, if the cooling system is that bad then the extra load of the boat should quickly show the same effect as the AC is I would have thought.
I'm also very keen to seem how well it pulls the boat, to be honest I'm not that impressed with my cars performance fullstop, my old Terrano diesel seemed to have more power... but may be that beacuse it wasn't fulltime four wheel drive (anyone ever tried the disco minus the front propshaft..?)
I'll keep you posted
Re: 1994 Discovery - Overheating
If it's heating up when loaded up (up a hill with the a/c on) then the main cooling system isn't coping. Both a slowly dying viscous fan and a old radiator that isn't 100% are common faults with Discos that are getting older.
I had a similar experience on my 90, it finally got bad enough that I did something... a new radiator fixed it, the old one was well past it. Then I checked the viscous fan which was also nearly dead... and replaced it. I used electric fans, but they aren't as powerful as a viscous fan so the only advantage is you can turn them off for wading through deep water. If you don't do that, just get another viscous fan.
A lot of people add another electric fan to their Disco when it starts to heat up, IMHO you are better off getting the radiator looked at or replaced as it is probably on the way out.
I had a similar experience on my 90, it finally got bad enough that I did something... a new radiator fixed it, the old one was well past it. Then I checked the viscous fan which was also nearly dead... and replaced it. I used electric fans, but they aren't as powerful as a viscous fan so the only advantage is you can turn them off for wading through deep water. If you don't do that, just get another viscous fan.
A lot of people add another electric fan to their Disco when it starts to heat up, IMHO you are better off getting the radiator looked at or replaced as it is probably on the way out.