Confused temp guage or owner
Discussion
Coming home this evening steady 65-70mph temp guage sat at 90 degrees without budging more than 1mm either way. On slowing down for 30mph area temp starts falling down to 75-85 range. Pick up speed again and temp rises to 90 once more. Engine runs fine and heater blows out heat. I'm slightly confused though.
Is it normal to have temp at 90 at speeds of 65-70 in this weather as I thought the air flow would be sufficient for cooling at this speed. (94 chim with lowered numberplate) Temp did drop when put on extra bit of speed for about a mile.
Is it normal to have temp at 90 at speeds of 65-70 in this weather as I thought the air flow would be sufficient for cooling at this speed. (94 chim with lowered numberplate) Temp did drop when put on extra bit of speed for about a mile.
I'd be a little concerned ...
As David says, the engine is producing much more heat at 70 than it is at 30. I've mounted an oil temp sender in the sump plug, and the temperature it reads is pretty much an increasing function of speed.
The water temperature is a balance between how much heat is being extracted from the engine into the coolant, and how much heat is being lost from the coolant into the air via the radiator.
Normally if the car is travelling at a reasonable speed the radiator's efficiency improves and dominates the balancing act between heat in and heat out of the coolant. Therefore the coolant temperature drops even though the engine's oil temp keeps rising.
One explanation for what you've seen is that for some reason your coolant is not losing heat as effeciently as normal from the radiator.
Two obvious possibilities are that the coolant level is low, or the flow through the radiator is partially blocked. There's a thermostatic valve thingy that stops coolant passing through the radiator until is is up to temp (helps engine get to running temp more quickly). I wonder if yours is beginning to pack up?
I guess it would also be worth checking that nothing is obstructing the flow of air through the radiator.
While I'm rambling on, it is not uncommon for the coolant temperature sender to pack up. (Obviously, it can be dangerous to automatically assume this is the case). You can use the oil pressure guage to give you a rough idea of the actual engine temperature. If the oil pressure is unusually low for the amount of work the engine is doing, it can be an indication that the oil is a lot hotter than normal. Again, there are plently of other reasons why the oil pressur may be low, and they may mean the engine is about to be lunched, so caution and common sense is required.
As David says, the engine is producing much more heat at 70 than it is at 30. I've mounted an oil temp sender in the sump plug, and the temperature it reads is pretty much an increasing function of speed.
The water temperature is a balance between how much heat is being extracted from the engine into the coolant, and how much heat is being lost from the coolant into the air via the radiator.
Normally if the car is travelling at a reasonable speed the radiator's efficiency improves and dominates the balancing act between heat in and heat out of the coolant. Therefore the coolant temperature drops even though the engine's oil temp keeps rising.
One explanation for what you've seen is that for some reason your coolant is not losing heat as effeciently as normal from the radiator.
Two obvious possibilities are that the coolant level is low, or the flow through the radiator is partially blocked. There's a thermostatic valve thingy that stops coolant passing through the radiator until is is up to temp (helps engine get to running temp more quickly). I wonder if yours is beginning to pack up?
I guess it would also be worth checking that nothing is obstructing the flow of air through the radiator.
While I'm rambling on, it is not uncommon for the coolant temperature sender to pack up. (Obviously, it can be dangerous to automatically assume this is the case). You can use the oil pressure guage to give you a rough idea of the actual engine temperature. If the oil pressure is unusually low for the amount of work the engine is doing, it can be an indication that the oil is a lot hotter than normal. Again, there are plently of other reasons why the oil pressur may be low, and they may mean the engine is about to be lunched, so caution and common sense is required.
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