fleabag

I noticed that the trend in all vehicles is towards lower weight motor oils and I found it interesting that this is happening. I then decided to look at the owner's manuals for the Honda Civics from '92-'05 and look at the maintenance charts, suggested oil types and whatnot. I found that the '92-'00 civics all suggest 5w-30 oil but the '01-'05 Civics suggest 5W-20 despite them all using the Honda D engine. Despite this, they also increased the service interval from 3750 for "Severe" to 5K and 5K to 10K for "Normal".
Curious thing is, the API oil Category has gone from SG all the way to SM now with SH, SJ and SL in between.

So I'm wondering, what could possibly cause or "allow" Honda to decrease the viscosity requirement from 30 to 20 but should be same physical engine block? I read that overtime, the viscosity rating declines for oils going from say 30 to 25 or something because of the shearing of the viscosity modifiers or something.. Could someone enlighten me as to how Honda was able to come to the conclusion that they could go from 30 to 20 or how vehicles that are already in service could have a TSB that issued stating that they now can use 5W-20 instead of 5W-30 like their owner's manuals state? Are these manufacturers monitoring the oil quality of these vehicles and are reevaluating whether the -30 rating is necessary or is it that they realize motor oils have gotten so much better than they were say only 10 years ago that they can handle more contaminants and not break down so quickly and become useless?

clutchrsx

The main reason 5W-20 was specified for your engine is to increase the CAFE (Corporate Average Fuel Economy) reported to the Federal Government. CAFE is the combined average fuel economy of all of a vehicle manufacturers product line. Minimum CAFE levels are specified by the Federal Government. In order for a vehicle manufacturer to continue selling profitable large trucks and SUV's, which typically have poor fuel mileage ratings, as compared to smaller cars, and still meet mandated CAFE requirements, they must also sell enough of the smaller cars which have much better fuel economy ratings to offset the poor fuel economy ratings of the larger vehicles. For model year 2001, the change to a 5W-20 oil will allow Ford and Honda's overall CAFE to increase by a very small amount, typically in the tenths of a mile per gallon range. 5W-20 oil is a lighter viscosity than a 5W-30 oil and therefore has less internal engine frictional losses, or less drag on the crankshaft, pistons and valvetrain, which in turn promotes increased fuel economy. This increased fuel economy is virtually undetectable to the average motorist without the use of specialized engine monitoring and testing equipment under strictly controlled test track driving when compared to a 5W-30, 10W-30 or a 0W-30 viscosity motor oil.


Basically for fuel economy purposes.


I've pondered this before as well

fleabag

How do you feel about this page:http://accuratecars.com/blog/2008/08...-automobiles/?

Also if fuel economy was so important, wouldn't they just pull out all of the stops and go with the 0w-20 oil instead of the 5w-20? I noticed that all the hybrid vehicles use 0w-20..

Scott_Tucker

I agree with the statement about CAFE. Vehicle manufacturers are trying to reduce friction and pumping losses as much as possible on their cars. It is in their best interest. If they can increase MPG one tenth of one percent by changing the viscosity they will.

There are several other reasons they have changed their requirements to a thinner oil and increased the change interval.

First, engine machining tolerances have gotten tighter over the years, especially in the last 20 years. As an example, the main bearing clearance is held a lot tighter. If the spec for main bearing clearance is .0011" to .0021" in the old days you might (in a new engine from the factory) have one main bearing with .0011" clearance and then the next one had .0021" and the next one was somewhere in between etc. That's .001" difference between the highest and lowest bearing and that is pretty huge. You need to use an oil which is suitable for the bearing with the most clearance which would mean a thicker oil. Todays engines may only have a difference of .0001" which allows you to specify a thinner oil.

Second, older engine did not have roller camshafts. The cam actually wiped across the surface of the rocker, not rolled. This necessitated a thicker oil with more high pressure additives in order to protect the camshaft. New engines all have roller camshafts.

The quality of base oil has increased dramatically over the last 20 years. A new process which removes a greater amount of wax than before was developed in the early 90's. This has increased the drain interval of the oil.

New engines run cleaner. Modern fuel injection allows the engine to run very clean. Much of the reason engine oil needs to be replaced is because it gets dirty. Much of the reason it get dirty is because of combustion byproducts which get past the rings ("blow-by"). Because modern fuel mixtures are a lot closer the the stoichiometrically correct mixture at all all times there is less "free" carbon in the byproducts of combustion. If you've ever seen the exhaust coming out of an engine that is running way too rich you will know what I mean. The smoke is dark black. This is carbon that did not get burnt in the engine. Older engines with early fuel injection and carburetors had to bias the fuel mixture richer in order for the engine to run well. Modern engines are able to run the fuel mixture leaner because of the finer control it has over fuel mixture, ignition timing, etc.

fleabag

That didn't require thicker oil, that required oil with more phosphorous in it which while good for lubrication is bad for catalytic converters. http://www.aa1car.com/library/api_mo...ifications.htm
Yeah but isn't that the difference between multiport FI and dual port FI? I mean by '92, weren't they already running pretty clean as it is?

Scott_Tucker

They were running much cleaner than a carbureted car but new cars have gotten even cleaner. Are you asking the difference between multiport fuel injection and throttle body injection? Multiport injection will always be cleaner because a throttle body injection system works very similar to a carburetor system.

fleabag

I did some more research and have discovered that the 5w-30 thing dates back not to '92 but to at least 1988! That's right, the '88+ Civics were recommending 5w-30 oil so until I read some owner's manual from prior to that, I think the fuel injected cars all run on 5w-30. I found it interesting that on one site it suggested that '96+ civics can now use 5w-20 oil but '95 and before should stick with the 5w-30 yet the clearances and service limits for the '92-'00 civics are the same (I haven't looked at the '88-'91). So to me, it would make sense that if a Honda D engine from '01+ can use 5w-20, I don't see why one from '88 can't either unless it is already so worn down that using that thin of oil would mean leakage (that's a separate issue though).