Engine Oil Thermostat Questions
09-09-2003, 04:34 PM
#1
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Engine Oil Thermostat Questions
Couple of questions about the oil thermostat.
Is the thermostat present on cars not equipped with an oil cooler?
If not present, OK to install oil cooler lines anyway?
Are the parts still available?
Can this be removed in favor of an external thermostat?
Is the thermostat present on cars not equipped with an oil cooler?
If not present, OK to install oil cooler lines anyway?
Are the parts still available?
Can this be removed in favor of an external thermostat?
09-09-2003, 08:14 PM
#2
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Porken-
I had all sorts of trouble finding an oil cooler tank for my '85 5 speed earlier this spring. I wound up fitting a non-cooler radiator and an external oil cooler.
The oil cooler was a Hayden unit [number 458, I think] that I found at an auto parts store. It uses a thermostatic sandwich plate, and I mounted the cooler itself in front of the radiator and low, where it is in the slipstream. It works fine, I guess- I don't have an oil temperature gauge to tell you just how cool it is running. I plugged the holes for the original oil hoses with "official" plugs from Devek.
A similar unit that I mounted on a VW Corrado VR6 a few years ago typically dropped oil temperatures 20 degrees F. On the 928, due to the length of the factory oil filter, I had to go with a Purolater L30251, which is listed for our cars and is about 1.5 inches shorter.
That was several thousand miles ago, and everything seems to be running well.
N!
I had all sorts of trouble finding an oil cooler tank for my '85 5 speed earlier this spring. I wound up fitting a non-cooler radiator and an external oil cooler.
The oil cooler was a Hayden unit [number 458, I think] that I found at an auto parts store. It uses a thermostatic sandwich plate, and I mounted the cooler itself in front of the radiator and low, where it is in the slipstream. It works fine, I guess- I don't have an oil temperature gauge to tell you just how cool it is running. I plugged the holes for the original oil hoses with "official" plugs from Devek.
A similar unit that I mounted on a VW Corrado VR6 a few years ago typically dropped oil temperatures 20 degrees F. On the 928, due to the length of the factory oil filter, I had to go with a Purolater L30251, which is listed for our cars and is about 1.5 inches shorter.
That was several thousand miles ago, and everything seems to be running well.
N!
09-10-2003, 01:18 AM
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Hi,
the 928's oil cooler thermostat opens to the cooler at 87C. I believe it is probably fully open at about 95C but it could be earlier
The oil cooler is an integral part of the 928's engine cooling system and the closer the oil and coolant are the better for the engine in general terms
It is very important that the oil is given a chance to reach at least 80-85C as often as possible. Oil that does not reach this temp. regularly or "normally" operates below it will deteriorate quite rapidly and lose its ability to control acid build up
It is quite possible that some 928's may not open their oil system thermostat very often at all - especially if the engine is using a 75C coolant thermostat and/or operating in extremely cold ambient temperatures
The optimum operating temperature for oil used in our cars is about the thermostat's opening temperature - say around 85-90C. Modern synthetic oils of the correct viscosity will operate around 110C with ease and the better ones are sound well beyond that. Some are very stable up to 150C which is the highest test rating point ( HT/HS )
In carrying out the Oil Condition Reports on my S4 and reported in here - next one due in October - I have noted that the maximum oil temp recorded has been 90C - recorded during our cooler months and at an ambient of 25C
Many early English cars and many MGBs/MGCs etc had non thermostatically controlled oil coolers and cold sludging was a real issue in these engines
as the oil temp often ran 30-40C cooler than the coolant
Regards
the 928's oil cooler thermostat opens to the cooler at 87C. I believe it is probably fully open at about 95C but it could be earlier
The oil cooler is an integral part of the 928's engine cooling system and the closer the oil and coolant are the better for the engine in general terms
It is very important that the oil is given a chance to reach at least 80-85C as often as possible. Oil that does not reach this temp. regularly or "normally" operates below it will deteriorate quite rapidly and lose its ability to control acid build up
It is quite possible that some 928's may not open their oil system thermostat very often at all - especially if the engine is using a 75C coolant thermostat and/or operating in extremely cold ambient temperatures
The optimum operating temperature for oil used in our cars is about the thermostat's opening temperature - say around 85-90C. Modern synthetic oils of the correct viscosity will operate around 110C with ease and the better ones are sound well beyond that. Some are very stable up to 150C which is the highest test rating point ( HT/HS )
In carrying out the Oil Condition Reports on my S4 and reported in here - next one due in October - I have noted that the maximum oil temp recorded has been 90C - recorded during our cooler months and at an ambient of 25C
Many early English cars and many MGBs/MGCs etc had non thermostatically controlled oil coolers and cold sludging was a real issue in these engines
as the oil temp often ran 30-40C cooler than the coolant
Regards
09-10-2003, 07:07 AM
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Doug-
I've often wondered about M28 oil temperatures, since I don't have any sort of gauge to monitor this.
Have you driven the car with the oil temp. gauge in 90 degree F/ 33 degree C ambient temperatures? If so, what are the typical oil temperatures? Is the car you are talking about equiped with the air-to-oil cooler or a radiator tank cooler?
-You've good points about not getting the oil warm enough to boil off condensate. Living in a warm climate, I doubt I ever run into this problem, especially since most of my driving is in stop and go traffic. I have the 75 degree thermostat kit, but I doubt my oil temps stay below 100 degrees C for very long.
Normy!
'85 S2 5 Speed
I've often wondered about M28 oil temperatures, since I don't have any sort of gauge to monitor this.
Have you driven the car with the oil temp. gauge in 90 degree F/ 33 degree C ambient temperatures? If so, what are the typical oil temperatures? Is the car you are talking about equiped with the air-to-oil cooler or a radiator tank cooler?
-You've good points about not getting the oil warm enough to boil off condensate. Living in a warm climate, I doubt I ever run into this problem, especially since most of my driving is in stop and go traffic. I have the 75 degree thermostat kit, but I doubt my oil temps stay below 100 degrees C for very long.
Normy!
'85 S2 5 Speed
09-10-2003, 07:58 AM
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Hi,
Normy - my car is a normal MY89 S4 with the radiator heat exchanger type oil cooler
I have not taken any oil cooler readings at an ambient of 90F/33C
but I expect that the oil will very rarely go much above 110C (as constant) unless you have limited airflow. Or if the cooling system is not good order
in a general sense.
Once the oil thermostat opens it is my experience that the temperature of the oil in the oil pan stabilises very quickly at about 10C to 15C above the coolant's temperature. If you have a reasonably constant engine load and good air flow of course
In dealing with oil temperature it is wise to remember that a multigrade oil's viscosity is "technically" thinner at colder temps. So optimally a 15w-50 oil is has a ( KV ) viscosity of 50 cSt at 100C. If measuring viscosity at a lower temperature - say at 90C - then "technically" it is thinner!
The chemicals in the oil are temperature sensitive but not in a linear manner so it is hard for the layman to calculate it in real terms. And not all oils have the same temperature driven characteristics of course
A 15w-50 oil ( mineral or synthetic ) will run marginally hotter than say a 5w-40 but will offer better film strength as the temperature escalates
In a general sense a synthetic oil will run marginally cooler than a similar viscosity mineral oil. It will handle higher temps better!
The rule of thumb then is to keep the oil temperature above 80-85C
I will of course continue to take engine temp readings as our Tropical summer kicks in and the ambient temps rise. And share the data on here
Regards
Normy - my car is a normal MY89 S4 with the radiator heat exchanger type oil cooler
I have not taken any oil cooler readings at an ambient of 90F/33C
but I expect that the oil will very rarely go much above 110C (as constant) unless you have limited airflow. Or if the cooling system is not good order
in a general sense.
Once the oil thermostat opens it is my experience that the temperature of the oil in the oil pan stabilises very quickly at about 10C to 15C above the coolant's temperature. If you have a reasonably constant engine load and good air flow of course
In dealing with oil temperature it is wise to remember that a multigrade oil's viscosity is "technically" thinner at colder temps. So optimally a 15w-50 oil is has a ( KV ) viscosity of 50 cSt at 100C. If measuring viscosity at a lower temperature - say at 90C - then "technically" it is thinner!
The chemicals in the oil are temperature sensitive but not in a linear manner so it is hard for the layman to calculate it in real terms. And not all oils have the same temperature driven characteristics of course
A 15w-50 oil ( mineral or synthetic ) will run marginally hotter than say a 5w-40 but will offer better film strength as the temperature escalates
In a general sense a synthetic oil will run marginally cooler than a similar viscosity mineral oil. It will handle higher temps better!
The rule of thumb then is to keep the oil temperature above 80-85C
I will of course continue to take engine temp readings as our Tropical summer kicks in and the ambient temps rise. And share the data on here
Regards
09-11-2003, 03:16 PM
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Nahmy - thanks for the reply, I remember your post from earlier.
Doug Hillary - thanks for the info, it's good to have bona-fide engineers on the board! (Not just wrench apes like myself
)
So far I've gathered (without having disassembled my own oil pressure system {yet}), there is no thermostat if you don't have the hoses.
I had planned to flip the radiator around, and use the auto trans cooler as the engine oil cooler. If I go this route, I will source the factory engine oil thermostat.
If I end up using an air/oil cooler like Normy, I will use an external oil thermostat (eg. Perma-Cool).
Doug Hillary - thanks for the info, it's good to have bona-fide engineers on the board! (Not just wrench apes like myself
)So far I've gathered (without having disassembled my own oil pressure system {yet}), there is no thermostat if you don't have the hoses.
I had planned to flip the radiator around, and use the auto trans cooler as the engine oil cooler. If I go this route, I will source the factory engine oil thermostat.
If I end up using an air/oil cooler like Normy, I will use an external oil thermostat (eg. Perma-Cool).
09-11-2003, 07:14 PM
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only engines with oil coolers have the thermostat . So 1980-1984 USA spec engines did not . Once the given temperature 87 C is reached the thermostat blocks one oil path and forces the oil to flow through the heat exchanger in the radiator . There is a pressure bypass which at about .5 to 1 Bar allows oil to not go through the heat exchanger .
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09-11-2003, 08:41 PM
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Jim - thanks!
Are the thermostat and the bypass springs still available new?
Are the thermostat and the bypass springs still available new?