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Discussion Starter #1
I'm changing to synthetics, I was using Pennzoil race oil 20w50 as recommended by my engine builder in 1981, GM gear oil in trans & rear. Changing to: Engine - Mobil 1 10w30, Trans - Redline MTL or Mobil 1, Rear, Mobil 1 with GM add. Unless enough of you disagree with my choices.


My main question is, is it better to change oil after or before running the car? I usually do it after running a little to warm it up but I'm thinking in this case I'm better off changing cold since most of the oil will be at the bottom because it's been sitting a couple days now which will give less mix of the 2 types of oil.

I have a 1970-1/2 LT-1 350 s/b from factory new in 1981 has around 15,000 miles on it.

Muncie M21 4spd trans.

12 bolt posi rear with Zoom 456 gears.

Thanks
 

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Myself I like to let it run for awhile before draining the oil.
 

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Ram Id run it till its almost fully warm, drive it around so the rear end is also warm. Then drain it down. That way you have a film of oil in the cylinders and bearing surfaces when you re-fire it again. You should notice a difference in switching over to syns too. Consider Amsoil since they have the full line of products, oil, gear lube and greases, all one brand.
Let us know what you 'feel' when you are out driving around then.
 

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Please don't throw any rocks guys!! ;) I do my oil changes cold, hate dealing with hot oil and exhaust pipes. Rational for doing it cold is the engine sets every night (or several days) before I start it. It's when the most wear is put on the internal parts but what's the difference if you start in before or after the oil change? Warm oil may drain a bit better but the difference left in the pan from a cold draining as opposed to a hot one has to be zip point zero. Hot you have have oil up in the heads and splashed everywhere that you won't be finding it's way to your drain pan in the time you put forth to do the service.

Mixing modern syn with dino oil is not a problem. 20 yrs ago it was and you needed to flush the system prior to introducing syn. A big change for the better!!
 

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Discussion Starter #5
Dennis,
That is what I'm thinking, It's starting dry either way and starting it after change it's getting syns right away. Glad to hear mixing is no longer a problem.

Click,
The only prob I have with Amsoil is it's not as local. That's why I'm leaning more towards Mobil 1 for trans also. Although I can get R/line thru parts store for $14 a quart, ouch! Thanks guys

Would still like more opinions.
 

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No scientific proof of course, but I always figured that right after the engine was run good and hot, all the impurities are mixed up real good in the oil and will drain out with the oil. I dont think it has anything to do with the next startup. If you have ever seen what accumulates in the bottom of a pan, you would want as much to flow out as possible every oil change.
Just my opinion,
 

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I'm with DJD on this one. I change my oil cold. The Camaro sits for weeks sometimes before a change < I work rotating shifts >.I feel as long as you change oil on a regular basis its not a problem. Last time I disassembled the 406 for a bearing check and new gaskets, all that was in the pan,lifter valley was some discoloration,no sludge at all. I do run straight 30wt. Valvoline...May this is why? <high detergent?>
 

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Hot is the only way I do it. Run it to temp and drain it right away, let it drain as long as you can, there's no hurry. Draining it cold will not allow more oil to drain. Any trapped oil in low spots or cylinder heads or where ever will be there hot or cold. Just allow enough drain time for everything to drain back like it is designed to.

Cold oil will be less likely to drain completely and will not move contaminant particles out since they have long since settled out into the low lying trapped areas. The reason to change oil in the first place in a piston engine is because it becomes contaminated even with normal engine use. It's these contaminants you want to remove from the engine and you can't do it if they've settled out of the oil.

I know it's no fun working with hot oil, but this is why all the Oil Analysis Labs request that you only send in oil for analysis that has been removed from the engine HOT. Otherwise all the metals and carbon grit have had a chance to settle out of the cold oil and your analysis of what's in your oil, and where the metal is coming from will be inaccurate.

[ 10-28-2003, 12:10 PM: Message edited by: SY1 ]
 

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SY that was just what I was going to add to my original post, that the testing MUST be done hot to give accurate test info. about the oil's content before it settles out in the pan.
For most folks it probably wont do a bit of damage by draining hot or cold BUT in the interest of a purist when it comes to my oil, the hot drain will remove more impurities. Kinda like Coke or Pepsi, Chevy or Ford, your choice.


Hey RamJam you dont have an email on your profile page, drop me an email, I can give you some info. on getting Amsoil at dealer cost.
 

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I never really put a whole lot of thought into it but I guess every time I change my oil the motor is warm because I have to drive from my house to my 'shop' then I usually let it sit so the exhaust cools off a little and I dont burn the crap outta my hand undoing the plug (oil ALWAYS manages to run right down the wrench onto my hand/arm)
 

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the best tool you can have for doing oil changes on a hot engine is a pair of mechanic's gloves. that way, a little bit of hot oil or the hot drain plug won't burn you so bad. i always have a few rags under there with me, just in case a bit of the oil runs down my arm. ever have hot oil run down your arm and under your shirt when you're twisting the filter off? that is NOT very fun at all.
 

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Got this link off the the Amsoil site. http://www.oaitesting.com/

From what I've read they want you to bring the temp up before samplings are taken to give a consistant sample. The cool oil in the pan tends to seperate. Here's a quote;

Never sample a cold engine and always make sure the oil has been well circulated before taking a sample. Dirt, water and other debris tend to settle to the bottom of the reservoir while light fuels tend to float. This separation will compromise your analysis.
From this quote they tell you the crud is in the pan (reservoir) so if you want to remove it why not just drain it off. If you are testing the oil that's different!!

They also don't recomend getting samples from the pan or filter;

Use samples from the drain pan or oil filter only as a last resort.
The recomendations are to avoid drawing false samples resulting in high or low concentrations of contaminates depending on where the sample was taken from.

Regular changes period are the key IMO not if the oil is hot or cold when you drain it. I've never had sludge build up in a pan on any personal vehicles engine that I've ever witnessed. Along with that I've never had an engine fail do to not heating the oil before draining. I have never lived in adversly cold climate that would effect the draining of oil from the pan and possibly leaving a residue in the pan.
 

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Dennis good info thanks. I know on some turbine engines you aren't even required to change the oil until the acid count is high enough on your report from the lab. That's a little scary for me, I don't know anyone who does that, I change it at regular frequencies anyways, regardless of the lab report. But oil in turbine engines serves a totally different role than in a recip piston engine.

Your comment about the cold climate took me back to the 70's when I was changing gear oil in the rear end of my 74 Z/28 in January in an unheated garage in Michigan. What was I thinking? Talk about slow going, but I was young and had a lot of time back then. LOL
 

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I'll go with the hot guys. When the engine is hot all the sediment and debri that is suspended in the oil will drain out when the plug is pulled. If you let an engine sit, all the crap you want out of your engine settles to the bottom and won't drain out when you pull the plug. I'd rather leave a little more oil in the engine after a hot drain than allow the crud to build up after each oil change. If anybody else said this in the previous post, my apologies. I didn't have time to read them all.
Jim
 
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