Is it common for filters to go into by-pass at cold starts and if so would this happen all the time or just when it’s around freezing temps
Filter By-pass Question
- Thread starter miata10ae
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I think it depends upon oil weight and temp, but I do believe filters go into bypass at startup.
Originally Posted By: Donald
I think it depends upon oil weight and temp ...
Other factors along with what Donald said above are: A) what the filter's bypass valve is set too, and B) how restrictive the filter is.
Key here is to keep the engine RPM at or near idle while letting the oil warm up some on very cold days before driving off.
I think it depends upon oil weight and temp ...
Other factors along with what Donald said above are: A) what the filter's bypass valve is set too, and B) how restrictive the filter is.
Key here is to keep the engine RPM at or near idle while letting the oil warm up some on very cold days before driving off.
Let me ask it this way. Using the filter and oil spec'd for your car. Is it common for the filter to by-pass when its cold.
Originally Posted By: miata10ae
Let me ask it this way. Using the filter and oil spec'd for your car. Is it common for the filter to by-pass when its cold.
Again, it depends on how cold and thick the oil is, and the other factors given above all play a part. The chances of it going into bypass are pretty certain if the oil if very thick due to cold weather and the engine RPM is well above idle before the oil warms up. Using a full synthetic oil in cold climates will stay more viscous and therefor help keep the filter out of bypass more often under the same temperature and engine RPM conditions.
The main reason a bypass valve exists is to open when the pressure differential across the media gets too great. That can happen if: A) Oil viscosity and flow it too high, thereby creating high delta P. B) The filter clogs up with crud which creates a high delta P. As more B) occurs, it takes less of A) to make the filter go into bypass.
Let me ask it this way. Using the filter and oil spec'd for your car. Is it common for the filter to by-pass when its cold.
Again, it depends on how cold and thick the oil is, and the other factors given above all play a part. The chances of it going into bypass are pretty certain if the oil if very thick due to cold weather and the engine RPM is well above idle before the oil warms up. Using a full synthetic oil in cold climates will stay more viscous and therefor help keep the filter out of bypass more often under the same temperature and engine RPM conditions.
The main reason a bypass valve exists is to open when the pressure differential across the media gets too great. That can happen if: A) Oil viscosity and flow it too high, thereby creating high delta P. B) The filter clogs up with crud which creates a high delta P. As more B) occurs, it takes less of A) to make the filter go into bypass.
Originally Posted By: miata10ae
Let me ask it this way. Using the filter and oil spec'd for your car. Is it common for the filter to by-pass when its cold.
Yes.
Even if the ambient temperature is 120 outside.
The by-pass senses pressure differential. So at start up, no oil is coming out of the filter. So the by-pass opens.
How quickly it closes is based on the other factors, such as cold ambient temps, thickness of the oil, contaminant within the element, etc.
Let me ask it this way. Using the filter and oil spec'd for your car. Is it common for the filter to by-pass when its cold.
Yes.
Even if the ambient temperature is 120 outside.
The by-pass senses pressure differential. So at start up, no oil is coming out of the filter. So the by-pass opens.
How quickly it closes is based on the other factors, such as cold ambient temps, thickness of the oil, contaminant within the element, etc.
You want the filter to bypass. You do not want a filter with pores big enough to allow cool oil (even 80°F) to flow through.
Originally Posted By: Filter guy
Originally Posted By: miata10ae
Let me ask it this way. Using the filter and oil spec'd for your car. Is it common for the filter to by-pass when its cold.
Yes.
Even if the ambient temperature is 120 outside.
The by-pass senses pressure differential. So at start up, no oil is coming out of the filter. So the by-pass opens.
How quickly it closes is based on the other factors, such as cold ambient temps, thickness of the oil, contaminant within the element, etc.
I really doubt an oil filter will be in bypass with oil at 120 deg F. Maybe, only if you started the engine and revved it to redline instantly after it started.
If a filter is clean, I really don't think filters go into bypass as much as people think. Even with cold thicker oil, the PSID across the filter is low, because with thicker oil the PD oil pump will go into relief mode quicker and put out much less flow volume output to the filter. A low volume of thicker oil going through the filter will produce about the same low PSID across the filter as a very large volume of hot oil going through the filter.
Originally Posted By: miata10ae
Let me ask it this way. Using the filter and oil spec'd for your car. Is it common for the filter to by-pass when its cold.
Yes.
Even if the ambient temperature is 120 outside.
The by-pass senses pressure differential. So at start up, no oil is coming out of the filter. So the by-pass opens.
How quickly it closes is based on the other factors, such as cold ambient temps, thickness of the oil, contaminant within the element, etc.
I really doubt an oil filter will be in bypass with oil at 120 deg F. Maybe, only if you started the engine and revved it to redline instantly after it started.
If a filter is clean, I really don't think filters go into bypass as much as people think. Even with cold thicker oil, the PSID across the filter is low, because with thicker oil the PD oil pump will go into relief mode quicker and put out much less flow volume output to the filter. A low volume of thicker oil going through the filter will produce about the same low PSID across the filter as a very large volume of hot oil going through the filter.
We had this discussion a year or so ago while Filter Guy was still on hiatus. We have lots of speculation on how often oil filters go into bypass, and when, but we didn't know. I think the discussion before was based on the Fram infomercial about how filters were made and they threw out some five figure number about how often it happens. We all knew the possible and probably times and danced around it hypothetically but nobody came up with an average number.
So, Filter Guy: given an engine with the correct filter for its application and the correct viscosity oil, how often, and when, is the bypass going to open over the average OCI? I'm hoping there are some industry rules of thumb available, or at least some design specs filter mfrs build towards.
So, Filter Guy: given an engine with the correct filter for its application and the correct viscosity oil, how often, and when, is the bypass going to open over the average OCI? I'm hoping there are some industry rules of thumb available, or at least some design specs filter mfrs build towards.
My '93 6.2 is a decent example-it definitely goes into bypass with straight 30 at fast idle on a cold start (even 50-55F)-it'll build quickly to 62 PSI and hold there, then gradually the idle oil pressure will drop to 30-35 when hot (granted it is the somewhat inaccurate GM factory gauge w/a new Delco sender). The bypass is in the block, but there is also a nitrile bypass on the filters I usually use (AAP Total Grips). It also is good at maintaining the pressure if shut off immediately-yesterday the OPS-actuated electric fuel pump continued to run for 30+ seconds when it was shut off (still cold).
Originally Posted By: bullwinkle
My '93 6.2 is a decent example-it definitely goes into bypass with straight 30 at fast idle on a cold start (even 50-55F)-it'll build quickly to 62 PSI and hold there, then gradually the idle oil pressure will drop to 30-35 when hot (granted it is the somewhat inaccurate GM factory gauge w/a new Delco sender).
The oil pressure will slowly drop at idle as the oil temperature increases and the oil starts thinning out. That's probably what you are seeing, which is completely normal - but not really a sign that the bypass valve opened and then slowly closed.
My '93 6.2 is a decent example-it definitely goes into bypass with straight 30 at fast idle on a cold start (even 50-55F)-it'll build quickly to 62 PSI and hold there, then gradually the idle oil pressure will drop to 30-35 when hot (granted it is the somewhat inaccurate GM factory gauge w/a new Delco sender).
The oil pressure will slowly drop at idle as the oil temperature increases and the oil starts thinning out. That's probably what you are seeing, which is completely normal - but not really a sign that the bypass valve opened and then slowly closed.
Originally Posted By: Jim Allen
We had this discussion a year or so ago while Filter Guy was still on hiatus. We have lots of speculation on how often oil filters go into bypass, and when, but we didn't know. I think the discussion before was based on the Fram infomercial about how filters were made and they threw out some five figure number about how often it happens. We all knew the possible and probably times and danced around it hypothetically but nobody came up with an average number.
Not sure if you've seen this test data from Purolator or not ... but it shows that with hot oil flowing at 12 GPM that the pressure differential across the filter is only ~5 PSI. 12 GPM is a huge amount of flow volume. Most garden hoses won't flow that much fluid.
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1930719&page=1
What has to be realized is that when the oil is colder and thicker the oil pump will shoot up to it's max pressure relief point much faster and will pump a much smaller volume of oil to the filter & engine oiling circuit. If the PD oil pump's pressure relief valve works well, then "theoretically" the pressure drop across the filter will be the same any time the pump is at max pressure output (ie, in pressure relief mode). In other words, the ratio of engine PSID to filter PSID (usually around 15:1) will remain the same if the pump can fully regulate the max input pressure to the filter & engine oiling circuit.
The caveat on this is that if the oil pump's pressure relief valve is not designed well enough to fully regulate the oil pressure and volume going to the filter & engine, then that could certainly cause excess flow to the filter and make it go into bypass because of greater PSID. This probably does happen at times, especially if an engine is started in very cold weather and the RPM is well above idle just after start-up.
We had this discussion a year or so ago while Filter Guy was still on hiatus. We have lots of speculation on how often oil filters go into bypass, and when, but we didn't know. I think the discussion before was based on the Fram infomercial about how filters were made and they threw out some five figure number about how often it happens. We all knew the possible and probably times and danced around it hypothetically but nobody came up with an average number.
Not sure if you've seen this test data from Purolator or not ... but it shows that with hot oil flowing at 12 GPM that the pressure differential across the filter is only ~5 PSI. 12 GPM is a huge amount of flow volume. Most garden hoses won't flow that much fluid.
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1930719&page=1
What has to be realized is that when the oil is colder and thicker the oil pump will shoot up to it's max pressure relief point much faster and will pump a much smaller volume of oil to the filter & engine oiling circuit. If the PD oil pump's pressure relief valve works well, then "theoretically" the pressure drop across the filter will be the same any time the pump is at max pressure output (ie, in pressure relief mode). In other words, the ratio of engine PSID to filter PSID (usually around 15:1) will remain the same if the pump can fully regulate the max input pressure to the filter & engine oiling circuit.
The caveat on this is that if the oil pump's pressure relief valve is not designed well enough to fully regulate the oil pressure and volume going to the filter & engine, then that could certainly cause excess flow to the filter and make it go into bypass because of greater PSID. This probably does happen at times, especially if an engine is started in very cold weather and the RPM is well above idle just after start-up.
As good an explanation as I've heard! I can't think of any way you would know your filter is in bypass unless you had a diff. pressure gauge attached and knew at what differential pressure your filter opened. That's why I wondered if the industry had any stats or averages on how many times the average bypass valve opened. They obviously have some design criteria for i, if you believe that Fram infomercial.
I am not an oil filter engineer, but I would think that the bypass valve is probably open on most oil filters after a cold engine start until the oil is warmed up to near the normal operating temperature. Engine oil at normal engine operating temperature is less viscous than at ambient temperature. It is really only important that the bypass valve is closed at normal oil temperatures and not during the brief period it takes the engine oil to warm up. In a healthy engine, the there will be insignificant engine wear from the unfiltered oil going through the bypass valve during warm up. To design a oil filter to not be in bypass on a cold engine start, the filter media area and overall size of the filter would need to be much bigger than would be needed for a filter that would come out of bypass once the engine oil is near normal operating temperature. This is unnecessary and I doubt the auto and filter makers would do this. It is important that the oil filter designers design the bypass valve to open at the appropriate pressure and be large enough to flow enough oil to prevent filter media damage from excessive differential pressure when the oil is cold. Ideally at the worst case conditions such as the guy who left 20W50 oil in their car and started in a Canadian or Alaskan winter.
Originally Posted By: hofcat
I am not an oil filter engineer, but I would think that the bypass valve is probably open on most oil filters after a cold engine start until the oil is warmed up to near the normal operating temperature.
I don't think they open as often as most people think. As I tried to explain above, when the oil is cold there is much less oil volume going through the filter due to the oil pump's pressure relief valve which regulates the max oil pressure, and hence the corresponding oil flow. As long as the engine RPM is keep low during warm-up, the bypass valve probably isn't going to open. If someone starts an engine in very cold weather and tears off down the road without much warm-up, then the bypass valve probably will open, as most oil pump's probably can't regulate very well under those extreme conditions.
1 or 2 GPM of cold oil flowing may produce about the same PSID across the filter as 10 or 12 GPM of hot oil ... and both would probably produce a PISD still below the bypass valve's opening pressure.
But as Jim Allen said above, the only real way to know is to have a delta pressure gauge across an oil filter in real world use scenarios to see how the bypass valve behaves.
I am not an oil filter engineer, but I would think that the bypass valve is probably open on most oil filters after a cold engine start until the oil is warmed up to near the normal operating temperature.
I don't think they open as often as most people think. As I tried to explain above, when the oil is cold there is much less oil volume going through the filter due to the oil pump's pressure relief valve which regulates the max oil pressure, and hence the corresponding oil flow. As long as the engine RPM is keep low during warm-up, the bypass valve probably isn't going to open. If someone starts an engine in very cold weather and tears off down the road without much warm-up, then the bypass valve probably will open, as most oil pump's probably can't regulate very well under those extreme conditions.
1 or 2 GPM of cold oil flowing may produce about the same PSID across the filter as 10 or 12 GPM of hot oil ... and both would probably produce a PISD still below the bypass valve's opening pressure.
But as Jim Allen said above, the only real way to know is to have a delta pressure gauge across an oil filter in real world use scenarios to see how the bypass valve behaves.
Originally Posted By: ZeeOSix
Originally Posted By: hofcat
I am not an oil filter engineer, but I would think that the bypass valve is probably open on most oil filters after a cold engine start until the oil is warmed up to near the normal operating temperature.
I don't think they open as often as most people think. As I tried to explain above, when the oil is cold there is much less oil volume going through the filter due to the oil pump's pressure relief valve which regulates the max oil pressure, and hence the corresponding oil flow. As long as the engine RPM is keep low during warm-up, the bypass valve probably isn't going to open. If someone starts an engine in very cold weather and tears off down the road without much warm-up, then the bypass valve probably will open, as most oil pump's probably can't regulate very well under those extreme conditions.
1 or 2 GPM of cold oil flowing may produce about the same PSID across the filter as 10 or 12 GPM of hot oil ... and both would probably produce a PISD still below the bypass valve's opening pressure.
But as Jim Allen said above, the only real way to know is to have a delta pressure gauge across an oil filter in real world use scenarios to see how the bypass valve behaves.
Agreed, without a test rig, it would be difficult to really know what is going on with the bypass valve. I am not that familiar with the oil pump bypass valves and what the engine makers set them to. Are they commonly set to be bypassing a some oil flow to the sump to maintain a steady oil pressure across a broad range of engine rpm? If so this would really be a oil pressure regulator and not just a simple pressure relief valve. I have never heard people refer to common car engines as having a oil pressure regulator vice a pressure relief valve. I suspect though that there are engines out there that have an oil pressure regulator vice a simple relief valve, especially larger displacement truck, stationary, and marine engines. Maybe some forum engine mechanics could at shed some light on this.
Originally Posted By: hofcat
I am not an oil filter engineer, but I would think that the bypass valve is probably open on most oil filters after a cold engine start until the oil is warmed up to near the normal operating temperature.
I don't think they open as often as most people think. As I tried to explain above, when the oil is cold there is much less oil volume going through the filter due to the oil pump's pressure relief valve which regulates the max oil pressure, and hence the corresponding oil flow. As long as the engine RPM is keep low during warm-up, the bypass valve probably isn't going to open. If someone starts an engine in very cold weather and tears off down the road without much warm-up, then the bypass valve probably will open, as most oil pump's probably can't regulate very well under those extreme conditions.
1 or 2 GPM of cold oil flowing may produce about the same PSID across the filter as 10 or 12 GPM of hot oil ... and both would probably produce a PISD still below the bypass valve's opening pressure.
But as Jim Allen said above, the only real way to know is to have a delta pressure gauge across an oil filter in real world use scenarios to see how the bypass valve behaves.
Agreed, without a test rig, it would be difficult to really know what is going on with the bypass valve. I am not that familiar with the oil pump bypass valves and what the engine makers set them to. Are they commonly set to be bypassing a some oil flow to the sump to maintain a steady oil pressure across a broad range of engine rpm? If so this would really be a oil pressure regulator and not just a simple pressure relief valve. I have never heard people refer to common car engines as having a oil pressure regulator vice a pressure relief valve. I suspect though that there are engines out there that have an oil pressure regulator vice a simple relief valve, especially larger displacement truck, stationary, and marine engines. Maybe some forum engine mechanics could at shed some light on this.
Originally Posted By: hofcat
I am not that familiar with the oil pump bypass valves and what the engine makers set them to. Are they commonly set to be bypassing a some oil flow to the sump to maintain a steady oil pressure across a broad range of engine rpm? If so this would really be a oil pressure regulator and not just a simple pressure relief valve.
In most cases it is a pressure regulator that is nothing more than a simple, spring loaded pressure relief valve. It's just a spring loaded valve that opens at a pre-set pressure to keep the oil pump outlet from going above a certain maximum oil pressure. Excess oil volume is shunted back to the sump or back to the pump's inlet, thereby keeping the outlet pressure and volume at the maximum level based on the oil's viscosity at that particular moment.
The oil flow volume going through the filter/engine oiling circuit is a direct function of the total flow circuit resistance (which is basically a constant), and the fluid's viscosity and oil pump's outlet pressure (which is the oiling circuit's inlet pressure).
So in other words, if the max outlet pressure of the pump is 80 PSI controlled by the pressure regulator (ie, relief valve), then the flow volume at 80 PSI with cold oil will be much less than the flow volume at 80 PSI with hot oil.
Most oil pumps will not even be able to hit the relief pressure point with very hot oil.
I am not that familiar with the oil pump bypass valves and what the engine makers set them to. Are they commonly set to be bypassing a some oil flow to the sump to maintain a steady oil pressure across a broad range of engine rpm? If so this would really be a oil pressure regulator and not just a simple pressure relief valve.
In most cases it is a pressure regulator that is nothing more than a simple, spring loaded pressure relief valve. It's just a spring loaded valve that opens at a pre-set pressure to keep the oil pump outlet from going above a certain maximum oil pressure. Excess oil volume is shunted back to the sump or back to the pump's inlet, thereby keeping the outlet pressure and volume at the maximum level based on the oil's viscosity at that particular moment.
The oil flow volume going through the filter/engine oiling circuit is a direct function of the total flow circuit resistance (which is basically a constant), and the fluid's viscosity and oil pump's outlet pressure (which is the oiling circuit's inlet pressure).
So in other words, if the max outlet pressure of the pump is 80 PSI controlled by the pressure regulator (ie, relief valve), then the flow volume at 80 PSI with cold oil will be much less than the flow volume at 80 PSI with hot oil.
Most oil pumps will not even be able to hit the relief pressure point with very hot oil.
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