Checking oil level???

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When you check your oil level why can't the engine be cold?? Does the oil have THAT MUCH thermal expansion when its warmed up? [Dummy!] I checked my oil in my truck when it was cold and it was at the bottom of the shaded region. I was wondering if i should add oil or should i drive it and then check it again. I really dont want to be driving it on low oil though... (if it is REALLY low). [ February 03, 2004, 08:43 AM: Message edited by: therion ]
 
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Well if you check it the first thing in the morning, after an overnight sit, and BEFORE starting your engine, the dipstick is usually pretty accurate. (On some cars it'll read a touch lower than with hot oil.) But if you start up a cold engine and then shut it off before the oil gets nice and hot (this takes quite a while), the oil gets hung up in the cylinder head, so the dipstick could be wrong. This is what you want to avoid...
 

therion

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quote:
Originally posted by quadrun1: Well if you check it the first thing in the morning, after an overnight sit, and BEFORE starting your engine, the dipstick is usually pretty accurate. (On some cars it'll read a touch lower than with hot oil.) But if you start up a cold engine and then shut it off before the oil gets nice and hot (this takes quite a while), the oil gets hung up in the cylinder head, so the dipstick could be wrong. This is what you want to avoid...
Ok yeah thats how i check it. Before i move the car i check the oil. Anyway looks like i'm a 1/2 quart low. I guess Mobil 1 SS 5W-30 and Amsoil 0W-30 aren't compatible. I recently topped off 1/2 quart of s2k and i noticed the oil level drop. I'll add 1/2-3/4 quart and see if I still have consumption issues. If so i will get rid of the oil and put in just s2k since i had some here. The truck has just 62,000 miles and has been taken care of so this can't be the engines fault.
 
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What I've found is...the thicker the oil, the greater the difference in levels between hot and cold...as much as 1/4 qt. with a 50 or 60 weight. In either case, unless your owner's manual specs. you check the oil hot...I like to check it cold ie. first thing in the morning. But, only with the condition that it was parked with a completely hot engine the night before. If the oil is not warmed completely ie. you're just moving the car into the garage or something (short distance driving), then there will be oil stuck up in the engine because it was pumped up and engine was shut off in a 'cold' state...and you will get an artificially 'low' oil level. Of course those using thinner 5-20/30's probably won't have this problem. In either case shutting it off hot and checking it cold seems to be the most accurate IMO.
 
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check the oil stone cold. I read somewhere the difference between checking hot and cold is 1/8 of a quart. you get an accurate reading checking stone cold IMHO. In my 92 car, I always checked cold. then I started checking when hot after reading posts here and I ended up overfillin causing a pan gasket leak [Mad]
 
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Cold engine, level ground. Check the oil level. Drive long enough to warm engine and oil. Park on level ground, wait 5 minutes. Check oil level. Note the difference if any, and now you have a reference point if you want to check level when hot (like on a trip). My old Dodge van showed 3/4 qt difference between cold and hot, using AMSOIL 10W-40 (this was about 20 years ago).
 
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You can check it hot or cold, but not in-between. Thermal expansion has a negligible effect. As quadrun1 explained, the oil gets hung up and may take a long time to drain into the pan. This is more significant if the oil is thicker. If you're driving hard enough to fully warm up the oil (ie: highway or extended city driving) and you stop at the gas station, it should be accurate after a few minutes. If you turn your vehicle on and idle it for 10 minutes, you'll probably have to wait half an hour or more for all the oil to drain back down, since idling doesn't warm the oil much and the thick oil will drain into the pan very slowly. I find the levels are about the same hot or cold for my car, but others may have noticed a difference, so it's probably best to follow Dick's instructions to get a reference point first. [ February 03, 2004, 02:18 PM: Message edited by: rpn453 ]
 

therion

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quote:
Originally posted by rpn453: You can check it hot or cold, but not in-between. Thermal expansion has a negligible effect. As quadrun1 explained, the oil gets hung up and may take a long time to drain into the pan. This is more significant if the oil is thicker. If you're driving hard enough to fully warm up the oil (ie: highway or extended city driving) and you stop at the gas station, it should be accurate after a few minutes. If you turn your vehicle on and idle it for 10 minutes, you'll probably have to wait half an hour or more for all the oil to drain back down, since idling doesn't warm the oil much and the thick oil will drain into the pan very slowly. I find the levels are about the same hot or cold for my car, but others may have noticed a difference, so it's probably best to follow Dick's instructions to get a reference point first.
Thanks for the help you guys. My last trip was kindof short (<4 miles) so I will drive it for 15 miles and then check the oil again. By the way the car sat for 3 days so far so dont you think the oil has set in the pan already?? [Frown] [Frown] [ February 03, 2004, 02:37 PM: Message edited by: therion ]
 
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I disagree. With the thicker viscosities eg. 15-50, drive until hot, shut off, wait 5 minutes and then check....level up to max. Then let sit overnight. Level will be about 2-3mm below the max line. Where did it go? I didn't believe it either until I started using 50 and 60 weights....never saw it with a 5-30. If anything the opposite was true...the level would be slighly higher (eg. ~.5mm) 12 hours after shutdown as more oil dripped down into the pan).
 

therion

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quote:
Originally posted by Dr. T: I disagree. With the thicker viscosities eg. 15-50, drive until hot, shut off, wait 5 minutes and then check....level up to max. Then let sit overnight. Level will be about 2-3mm below the max line. Where did it go? I didn't believe it either until I started using 50 and 60 weights....never saw it with a 5-30. If anything the opposite was true...the level would be slighly higher (eg. ~.5mm) 12 hours after shutdown as more oil dripped down into the pan).
its on the bottom of the shaded area.
 
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In reality, it depends on the amount of oil in your crankcase, the ambient temp compared to a "hot" engine, and the engine design. Oil expansion due to temp. is directly related to API gravity, and NOT viscosity. OK, if your oil pan holds 4 quarts and you get a 1% expansion from 60 deg to 120 deg., you may gain that 1/8 quart (actually about 1.5 oz.). Now consider a car that holds 7.5 quarts, or a truck that holds 20 quarts, and make the crankcase full at -20 and you will see a HUGE difference when hot. This is partly why transmissions (18 quarts) are always checked HOT. I've said this before (last week in fact when this subject was last posted) FOLLOW THE MANUFACTURERS RECOMENDATIONS TO THE LETTER!
 

Kestas

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When I check it on some cars cold, the level is way up (about two inches) above the max line. I don't know why that is except that somehow the oil seems to get sucked up the tube overnight. In that case I have to wipe off the dipstick, wait a few minutes for fluid to drip down the tube, reinsert, and check level. Makes it a real pain to check it properly according to manufacturers specs.
 
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quote:
Originally posted by rpn453: You can check it hot or cold, but not in-between. Thermal expansion has a negligible effect.
You’re wrong, dummy. [Dummy!] Sorry about that. Most solids and liquids I’ve encountered don’t have high expansion rates like petroleum products. Based on thermal expansion rates at 15C published in my Esso Product Information guide, and assuming a linear rate of thermal expansion in the temperatures seen by motor oil, the volumetric expansion of motor oil increasing by 70C is about 16%. So that’s more than a liter on an 8 liter sump. Quite significant! The assumption of a linear rate of thermal expansion is not highly accurate for a fluid with such temperature-dependent properties, but it should give us some ballpark values. Maybe the effects of thermal expansion and oil hang up come close to canceling each other out for my vehicle at full operating temp, since I don’t see a wide variation when I check my oil hot versus cold. I guess you just have to know the characteristics of your particular vehicle. Establish references so that you can check your oil cold and still make sure your oil level is OK when you’re stopping for fuel on a highway trip.
 
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quote:
Originally posted by rpn453:
quote:
Originally posted by rpn453: You can check it hot or cold, but not in-between. Thermal expansion has a negligible effect.
You’re wrong, dummy. [Dummy!] Sorry about that. Most solids and liquids I’ve encountered don’t have high expansion rates like petroleum products. Based on thermal expansion rates at 15C published in my Esso Product Information guide, and assuming a linear rate of thermal expansion in the temperatures seen by motor oil, the volumetric expansion of motor oil increasing by 70C is about 16%.

With your 16% volumetric expansion in a 55C temperature change statement, I hope you were looking in the mirror when you made your dummy comment [Smile] [Smile] [Smile]
 
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If the ADBV on your oil filter doesn't hold the oil in the filter & galleys, then there can be a dramatic difference in the oil level at times when the engine is cold. In my opinion you're better off checking the oil when the car is hot because you know that the filter and galleys are filled with oil. The car manuals that I've read say to check the oil at each gas fillup. Since you have to drive to the gas station, they assume you will check it hot.
 
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My Chevy owners manual recommends checking the oil at each gas fill up parked on level ground with the engine war. After allowing a few minutes for the oil to flow back to the pan.
 
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Heres a relevant question: Scenario - Two different readings, about a 1/5-1/6 of a qt., when oil is checked 'hot' (~100 C) to when checked at normal operating temp (~40-50 C). The 'hot' temp shows the higher reading. 1. 5w30 Redline oil both cases 2. oil checked at gas station in both cases 3. Waited 3-5 minutes when the oil was at normal; around 7-10 minutes when oil was at 'hot' temp 4. Keep in mind, these oil temp readings are a rough estimate at best but the control here is the conditions - in terms of load and rpms (i.e. 'hot' temp was achieved by redlining 2nd, 3rd, and part of 4th on roughly six occasions, with a steep grade ascent in three of those in 45 F temp range; the normal operating temp was reached by driving the vehicle at around 2500-3K rpm for ten minutes) Why the variance in readings with the same oil? [I dont know] I don't believe the additional 'wait' time for the two readings would affect the readings this much, or could they? [ February 08, 2004, 06:28 PM: Message edited by: RC211V ]
 
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NOW you've done it RC211V! Now I have three oil levels to worry about, COLD, NORMAL, and HOT! Just when I thought I had 3000 mile oil changes figured out. [Eek!]
 
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Johnny, Welcome to the world of lubrication. [Coffee] Honestly, I would follow the manufactures recommendations, but if you have a discrepency, as in my case, then you have something to worry about, like me. [Razz] Can anyone help?
 
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