Not hot but gauge high
#1
06-20-2017, 07:06 AM
Not hot but gauge high
So this morning I ran Jessie up to temperature to test things. I had got a high temp reading and got a bit worried.
Tstats open at around 85 and upper rad tubes start warming. Check gauge. Over the top of the N! Pull lead off temp gauge sending unit. Gauge reads flat at bottom. Clean it up nice and reattach. Gauge reads over the N!
check it with the laser thermometer. 87C. At the sending unit. Put a finger on the sending unit housing. Three seconds before I need to pull away.
Sending unit is bad right? Right!?
Tstats open at around 85 and upper rad tubes start warming. Check gauge. Over the top of the N! Pull lead off temp gauge sending unit. Gauge reads flat at bottom. Clean it up nice and reattach. Gauge reads over the N!
check it with the laser thermometer. 87C. At the sending unit. Put a finger on the sending unit housing. Three seconds before I need to pull away.
Sending unit is bad right? Right!?
#2
06-20-2017, 07:36 AM
Most likely.
Has the instrument unit been cleaned, and the flex PCB contacts cleaned. Paying particular attention to the 2 multi pin connectors at each bottom corner.
Then the additional earth wire attached to a known good earth point on the bodywork just under the front screen??
Air in the cooling system also has that affect.
Has the instrument unit been cleaned, and the flex PCB contacts cleaned. Paying particular attention to the 2 multi pin connectors at each bottom corner.
Then the additional earth wire attached to a known good earth point on the bodywork just under the front screen??
Air in the cooling system also has that affect.
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Greg in France (06-20-2017)
#3
06-20-2017, 07:47 AM
Veteran Member
Those temperatures are quite OK. The importance of the gauge is ONLY so you know where the needle will be if the car is at normal operating temperature (which yours was). So if, for some reason it is above the N a touch when the exit temp of the water is 87, all is fine. A new sender may reduce the gauge indicated temp (may not) but it will NOT affect the actual temperature!
My car has the stage 1 Lutz mod (a procedure whereby water from the pump is guided more to the rear of the engine than standard). One effect of this is to make the gauge read higher at normal, as cooled water is not preferentially short-circuiting full circulation through the engine through the front water manifold. Obviously this means hotter water going past the sender as the sender is on the front A bank water manifold - which is now receiving more water from the rear of the engine than before. On my car at water pump inlet temperature of 90 C (the temp at which my main fan cuts in) the gauge is 40% of the way between the N and the H. Nothing to worry about, as I know that is what it means.
As far as overheating goes, steam cavities or actually low coolant levels caused by leaks or poor bleeding, are the killers, NOT high temperatures on their own. Of course, higher temperatures mean more likelihood of disastrous trouble, but if the cooling system is 100% they will not cause it on their own.
Recently I did a 400 mile trip to the South of France, and had a 90kph tail wind for the last 130 miles, which did no favours at all to the cooling system. Added to which one of my two electric fans failed because of a poor connector. In traffic at the end of the journey, still with a massive tailwind, the needle went to about 5mm below the H, but no water loss and no engine damage, because coolant was not cavitating into steam. I cannot say I wasn't nervous though! But I would not have been in that position with both fans going.
As a matter of fact, anyone who is (in my view) misguided enough to put waterless coolant into their V12, will ALWAYS have the engine running at these elevated temperatures. Allegedly, the engine will be OK because there will be no steam pockets.
Greg
My car has the stage 1 Lutz mod (a procedure whereby water from the pump is guided more to the rear of the engine than standard). One effect of this is to make the gauge read higher at normal, as cooled water is not preferentially short-circuiting full circulation through the engine through the front water manifold. Obviously this means hotter water going past the sender as the sender is on the front A bank water manifold - which is now receiving more water from the rear of the engine than before. On my car at water pump inlet temperature of 90 C (the temp at which my main fan cuts in) the gauge is 40% of the way between the N and the H. Nothing to worry about, as I know that is what it means.
As far as overheating goes, steam cavities or actually low coolant levels caused by leaks or poor bleeding, are the killers, NOT high temperatures on their own. Of course, higher temperatures mean more likelihood of disastrous trouble, but if the cooling system is 100% they will not cause it on their own.
Recently I did a 400 mile trip to the South of France, and had a 90kph tail wind for the last 130 miles, which did no favours at all to the cooling system. Added to which one of my two electric fans failed because of a poor connector. In traffic at the end of the journey, still with a massive tailwind, the needle went to about 5mm below the H, but no water loss and no engine damage, because coolant was not cavitating into steam. I cannot say I wasn't nervous though! But I would not have been in that position with both fans going.
As a matter of fact, anyone who is (in my view) misguided enough to put waterless coolant into their V12, will ALWAYS have the engine running at these elevated temperatures. Allegedly, the engine will be OK because there will be no steam pockets.
Greg
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Grant Francis (06-20-2017)
#4
06-20-2017, 08:43 AM
Just to clarify, she normally reads just at the bottom of the N.
no damage or changes to the cooling system, coolant levels are normal.
Instrument cluster has been pulled and cleaned and is in good shape connector wise. Extra ground was not added at that time. All other gauges behaving normally.
I am am curious if you are saying that air pockets can cause high readings in the gauge, or just high temps in the air pocket area. The later is obvious, as air does not transfer heat away like fluids do. But if you're saying air can also cause high gauge readings then I'm confused, as the same applies to transferring heat to the sensor. Air in the sending unit cavity would cause a lower than expected reading; I think.
no damage or changes to the cooling system, coolant levels are normal.
Instrument cluster has been pulled and cleaned and is in good shape connector wise. Extra ground was not added at that time. All other gauges behaving normally.
I am am curious if you are saying that air pockets can cause high readings in the gauge, or just high temps in the air pocket area. The later is obvious, as air does not transfer heat away like fluids do. But if you're saying air can also cause high gauge readings then I'm confused, as the same applies to transferring heat to the sensor. Air in the sending unit cavity would cause a lower than expected reading; I think.
#5
06-20-2017, 09:44 AM
Veteran Member
Just to clarify, she normally reads just at the bottom of the N.
I am am curious if you are saying that air pockets can cause high readings in the gauge, or just high temps in the air pocket area. The later is obvious, as air does not transfer heat away like fluids do. But if you're saying air can also cause high gauge readings then I'm confused, as the same applies to transferring heat to the sensor. Air in the sending unit cavity would cause a lower than expected reading; I think.
I am am curious if you are saying that air pockets can cause high readings in the gauge, or just high temps in the air pocket area. The later is obvious, as air does not transfer heat away like fluids do. But if you're saying air can also cause high gauge readings then I'm confused, as the same applies to transferring heat to the sensor. Air in the sending unit cavity would cause a lower than expected reading; I think.
Greg