Wandering temp needle
Discussion
Hi all, just before I put the chim away for the winter months I noticed the temp gauge needle occasionally wandering much quicker than normal. I know the cooling fans take a different signal and these kick in as normal.
I presume this is just the sender but we were away in it last weekend and I had the occasional whiff of hot coolant which isn't usual. Could these be connected? Everything else including g coolant level absolutely normal.
I presume this is just the sender but we were away in it last weekend and I had the occasional whiff of hot coolant which isn't usual. Could these be connected? Everything else including g coolant level absolutely normal.
The clue is in the 'whiff of coolant'!
If you can smell it then it's getting out and more importantly air is replacing it. The wandering gauge is most likely due to a slug of air circulating the system. When air passes through the coolant pump it stalls flow, fortunately this is a short lived stall as localised hot spots then boil the coolant which kick starts coolant flow. The result is massive differences in coolant temperature throughout the system. There is also an issue with the location of the coolant sender. TVR had to fit a boss because their sender was a different thread to the threaded socket they used. This means that the sender probe is not adequately immersed in the coolant flow. If air develops around the sender it can stick there making response time slow. Many owners have done the 'Rover temperature mod' to improve response time though there are issues with accuracy during warm up with this mod due to a 'fix' that is needed to make it accurate at normal running temperature
If you can smell it then it's getting out and more importantly air is replacing it. The wandering gauge is most likely due to a slug of air circulating the system. When air passes through the coolant pump it stalls flow, fortunately this is a short lived stall as localised hot spots then boil the coolant which kick starts coolant flow. The result is massive differences in coolant temperature throughout the system. There is also an issue with the location of the coolant sender. TVR had to fit a boss because their sender was a different thread to the threaded socket they used. This means that the sender probe is not adequately immersed in the coolant flow. If air develops around the sender it can stick there making response time slow. Many owners have done the 'Rover temperature mod' to improve response time though there are issues with accuracy during warm up with this mod due to a 'fix' that is needed to make it accurate at normal running temperature
Deebeezee said:
Thanks for the replies. That makes sens Bobfather although I have had a good look around and can't see anything. There is nothing on the floor and level doesn't seem to have dropped. Any place it could be leaking from which is difficult to spot?
The level in the expansion pot may have slowly lowered to a point when there was no coolant there, that can happen without any outward signs. Once that happens air is in the system. The hot spot boiling I mentioned then over pressures the system throwing coolant out of the expansion pot cap. This turns to steam leaving little evidence other than a smell of antifreeze. It also unfortunately leaves a level of coolant in the expansion pot thereby misleading people into thinking the system is full.Take the cap off the swirl pot. If there is air in there then low coolant level is your problem
Thought I would update this thread after curing the issue.
Bobfather pretty much on the money, the leak eventually presented itself in the form of dampness at the bottom of the rad. There was a small split where the core meets the end plate which £40 later was repaired.
I took the opportunity to replace all the hoses whilst the rad was out and also fit a new Range Rover temp sender in the original sender location with an inline 150ohm resistor in place.
I was frustrated at first as the rapidly wandering needle was still present after refilling with coolant and bleeding but a week later and further bleeding and the guage is now rock solid. It's really odd seeing it warm up quickly and sit just over 80 degrees and not move unless it's really hot when it wanders to about 88.
Cheers for the advice! If anyone wants to know more about the new sender and resistor give me a shout
Bobfather pretty much on the money, the leak eventually presented itself in the form of dampness at the bottom of the rad. There was a small split where the core meets the end plate which £40 later was repaired.
I took the opportunity to replace all the hoses whilst the rad was out and also fit a new Range Rover temp sender in the original sender location with an inline 150ohm resistor in place.
I was frustrated at first as the rapidly wandering needle was still present after refilling with coolant and bleeding but a week later and further bleeding and the guage is now rock solid. It's really odd seeing it warm up quickly and sit just over 80 degrees and not move unless it's really hot when it wanders to about 88.
Cheers for the advice! If anyone wants to know more about the new sender and resistor give me a shout
Edited by Deebeezee on Monday 2nd July 20:50
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