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Discussion Starter #1
Its time to get my oil changed, so im wondering which one to buy, what do you think about 5w50 for my DOHC ZC (d16a9) ? Or better 10-40 ? Car is mostly driven in high revs...
 

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1988 Honda CRX
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What is the condition of your engine.

What is the climate where you drive.

Is it street or race.
 

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Discussion Starter #3
Streetrace :D

Good condition, no smoke on full throttle.

Winter very cold and summer very hot :)


Not sure if 5w50 is good for bearings
 

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For very variable conditions on an old engine in reasonable condition, I would think 5W50 is an OK choice for hard street use.
 

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Discussion Starter #5
Sorry but what you think about a3/b3 standards in oil which are best for Honda engines? Some 5w50 are not a3/b3, should i try it anyway ?
 

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91 Civic
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i always geat 10w-30 (mild east coast), i also dog te shit out my motor and burn very little if non. ive been told by my honda teacher that if you put thicker oil in your motor it will wear the bearings quicker as the clearance are to tight to fit such a thick oil...
 

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If you read the FSM, you will see it recommends different weight oil for different climate.

Also engines with lots of miles on them have wider clearences than when they where new.

Oil thins out with heat. As well as climate, hard driving increases the temperature of the oil.
 

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93 Legend L Coupe.
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It seems like you have no idea how to determine the "thinness" of engine oil. I have put on too many miles to think about on my internally stock DOHC ZC with 10 or 0w30 (0 because I was stationed near Canadia and it stayed under freezing for months at a time), and even after I swapped on the turbo, I kept the 10w30. Use quality oil and stop reducing the volume of flow to the engine with oil that is not designed to flow well enough to lubricate properly. =/
 

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They call me Awesome!
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but is it true that also a thin oil can make a bearing fail ?
Depends, oil has different viscosity at different temperatures; i.e. if it's cold it's thick and if it's warm is thin. So what temperature is your oil operating at?

Also, the clearance of your bearings between crank and caps will require different "thickness" of oil. So what are you bearing clearances?

Or you could just run the OEM recommended weight...
 

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1992 Civic DX Hatch
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Thin oil lubricates sooner because it moves faster. A SBC with a bunch of miles on it will have sufficient clearance for thick oil to move thru it pretty quickly, an import with its tighter tolerances may never have enough clearance to run thick oil. Most wear occurs at start up because there is not enough oil flowing to make a cushion of oil to reduce friction. The tighter the tolerance and the thicker the oil the longer it takes to build up this cushion.

Stay with the 10W30
 

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Thin oil lubricates sooner because it moves faster. A SBC with a bunch of miles on it will have sufficient clearance for thick oil to move thru it pretty quickly, an import with its tighter tolerances may never have enough clearance to run thick oil. Most wear occurs at start up because there is not enough oil flowing to make a cushion of oil to reduce friction. The tighter the tolerance and the thicker the oil the longer it takes to build up this cushion.

Stay with the 10W30

You do realise an oil pump is a positive displacement pump. In theory if the pump seals perfectly, it pumps exactly the same volume of oil no matter what viscosity. As the galleries have exactly the same volume they fill just as quick.

Only difference occurs when the pressure relief valve pops open, and by that stage even heavy weight oil is flowing rapidly to the bearings and you would basically need grease to open a pressure relief valve at cranking speed..

Also if the pump is worn and does not seal well, light oil blows past the rotors or gears more easily and in fact takes longer to prime and get oil to the bearings.

Bearings do wear and increase clearance, otherwise the oil pressure would never drop off in old worn engines. In fact a drop in oil pressure is a real indication of wear.
 

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I do not mean any disrespect and I do see you all over this website handing out really good advise , and I do realize the oil pump is positive pressure, I also realize that thinner oil will move farther through the system in the same amount of time providing better earlier lubrication. It is one of the main advantages of synthetic oil. Synthetic oil has consistent size molecules unlike petroleum oil. It is also the reason some people experience oil leaks when they change over to synthetic oil. Synthetic oil will flow more at lower temperatures often finding leaks that petroleum oil cannot get to until it is much warmer and by that time expansion from heat may have caused the seals to expand and close them up. I know we are talking small sizes here and at some point to large of a gap will negate this advantage. A good example of this is a dirt track race engine. Main bearing clearances are very large for freer rotation they want that thing to zing up and down the RPM range. In that case they would use a thicker oil to meet that specific need. I have see dirt trackers run main bearing clearances of .008 to .010 which would be absurd for a daily driver. I would not move up from 10W30 unless I saw signs of wear like lower oil pressure. But that only prolongs the unenviable when you are slowly loosing oil pressure parts of your engine are wearing out.
 

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Just a example of different oil spec's

LUBRIPLATE 981 Natural Gas Compressor Lubricant

Viscosity cSt @ 40°C 84.4
Viscosity cSt @ 100°C 16.5
Viscosity Index 218
Pour Point, °C -45
Flash Point, COC, °C 275
Specific Gravity, 60°F 1.042

LUBRIPLATE 989 Synthetic Compressor Lubricant

Viscosity cSt @ 40°C 138
Viscosity cSt @ 100°C 24.4
Viscosity Index 224
Pour Point, °C -42
Flash Point, COC, °C 245
Fire Point, °C 270
Specific Gravity, 60°F 1.052
 

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An oil pump is positive displacement. That is the point. All pumps are positive pressure on the outlet side otherwise they would not pump.

Large clearances do not make for freer rotation. Enough clearance for the crank to sit on a thin film with no metal to metal contact is all it takes for minimum friction. In fact tightish clearances which allow light oil have less friction than larger clearances that require thick oil.

Sprint cars run large clearances because they run endurance races on methanol. As methanol needs a bit over twice as much fuel as petrol, you get a lot more past the rings into the oil. This thins the oil and reduces its lubricating power, so you need the oil to be thicker to cover the loss.

Also as the quality of lubrication decreases due to methanol dilution, the bearings run hotter and the journal expands and reduces clearance. If you don't have enough to start with you soon end up with zero and a spun bearing.

Another reason that Sprint cars need more clearance than a Honda is that the blocks and cranks distort more from each power stroke. You need enough clearance so it does not bind from the distortion.

I have built a few SBC Sprint Car Engines. We ran 0.003" to 0.004" clearance with competitive engines with no bearing problems. I actually know a guy who runs a heritage Top Fuel Dragster with a blown nitro methane fueled SBC. He is making about 3000hp. Nitro runs about 6 to 7 times as much fuel as petrol, so oil dilution is extreme. He runs 0.004" to 0.005" clearance. To compensate for his 0.005" clearance he uses a very large pump and 70 wt oil.

Seepage past a seal being pushed by gravity, capillary action, centrifugal force and crankcase pressure has absolutely nothing to do with flow through the galleries and bearings when pushed by a positive displacement pump.
 
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