Why did oil consumption drop??

[VolvoBruce]

'97 Civic, 92K Miles, 5-speed. SOHC, VTEC-E engine.

My question is: Did consumption drop because I gradually added 20 oz. of 20W-50 when topping off the disappearing 10W-40? Or dropped because that 20W-50 was Castrol dino and not the Supertech Conventional 10W-40 that was already in the sump?

When the weather warmed up recently, and ECT now typically 185-195 deg F vs. ECT about 177-185 in winter, oil consumption increased from about .75 qt/1000 miles to more than double that, running 5w30 conventional which is spec'd for the car. I did an oil change and put in 10W-40 Supertech Conventional. Here's how it played out:
(odometer readings)
191,310 - 191,864: took 22 oz = 1.24 qt/1000 miles
- - - - on 10W-40 Supertech Conventional oil.

191,864 - 192,200: took 10 oz = .93 qt/1000 miles
- - - - running with 15 oz. 20W-50 Castrol used to top off the 10W-40 during the 336 mile run.

192,200 - 192,384: no consumption detected in 184 miles
- - - - I'd added 5 oz at the 192,200 mark so it ran these 184 mi. with 20 oz of 20W-50 Castrol.

It had a rough idle and occasional misfires reported by the OBDII check engine light. No CELs after adding 15 oz. 20W-50 to the system, and a smoother idle.

I've been meticulous about tracking the ounces, parking in level spots, even letting it sit an hour or more before doing a final level check. The sump is too small and consumption too fast to let it go 1000 miles between topoffs. I must admit, I'm a detail guy.

 

[ARCOgraphite]

5w30 and 10w-40 are "BAD" oils for consumption because the majority of the viscosty maintainence is the viscocity improver polymer additive. The base oils truely are near their W ratings of SAE 5 and 10 and "goop" is added to maintain hot viscocity. A More stable oil would be a 10w30, 15w40 or 15W or 20W 50. I see no need for the 50 as the 30 or 40 should do the "trick" and the 50 is just wasting fuel in that engine. Try a full sump of 10w30 HDEO next time like Shell RT-5 or in a PCMO Pennzoil 10w30 HM is "weighty", for a budget Formula shell 10w30.

 

[brandini]

"A 10w30 multigrade mineral based oil is made from a 10 weight oil and has VI improvers added to thicken the product in a 212 F engine. It acts as a 30 weight oil when hot. It acts more as a 10 weight oil at startup. A 10 or 5 or 2 weight oil is still too thick to provide lubrication at startup.

A 10w30 synthetic oil is based on a 30 weight oil unlike the counterpart. There is no VI improver needed. Synthetic oil is already correct for the normal operating temperature of 212 F. It will never thin yet has the same long term problem as the mineral based oil. They both thicken with extended age.

A Synthetic 10w30 weight oil is based on a heavier 30 weight oil while the mineral based 10w30 oil is based on a thinner 10 weight oil. They are both similar at operating temperatures yet the 30 weight based synthetic is actually less thick at startup and much less honey-like at low temperatures. This is the opposite of what common sense dictates."

I'd say it's covering the problem of a worn engine pretty well by giving you a thicker film and sealing rings/valves better.

 

[VolvoBruce]

brandini,

Looks like you're suggesting 10w30 synthetic.

I tried a batch of WalMart synthetic 5w30, in warm weather. That stuff went through the engine faster than anything else I used.

10W-30 isn't 5w30, I admit. You think synthetic 10w30 would be a good idea? Stay away from walmart???

 

[brandini]

Start at a 10w30, then go thicker until you get the results you want. It may not be the best for mpg but your engine should last longer. I wonder what a compression or leakdown test would reveal.

 

[VolvoBruce]

Compression test 11/17/09, ~179K miles on the clock. Now 192K, 4/2010.

Cyl. # 1-2-3-4:
200-190-187-180 psi, dry.
#4 w/oil added, 215 psi (I didn't want to restst them all)

Coasted down a long hill with engine spinning about 4k rpm.
Hit the gas at the bottom; blew a good sized cloud of smoke out the tailpipe, visible in rear view mirror.

ARCOgraphite, I like your suggestion. Still not sure which way I'll go firhgt now.

 

[fdcg27]

I guess you mean that the basestocks had no VI, so all of the spread had to be achieved with VIIs?
I agree that a 10w30 HDEO might be appropriate.
Mobil 1 15W-50 is also fine for a Honda in warm weather, based upon my real world, my engines don't self-destruct in a few tens of thousands of miles, experience.

 

[VolvoBruce]

CORRECTION
Car has 192K. I only left off a "1" when I first posted the thread, no biggie, right?

 

[mechtech2]

20-50 is thicker - it burns less and leaks less.

 

[VolvoBruce]

OK - thanks, all.

I bought a jug of Pennzoil High Mileage 10w30 conventional. Hopefully it will hold its viscosity better than the various 5w30s and the Walmart SuperTech 10w40 that I tried.

Also grabbed a 2nd small bottle of Castrol 20-50 just in case it burns through too fast.

However if the 10-30 runs through the engine too quickly I'll likely change it out quickly for some 15w40 conventional hdmo diesel oil.

 

[ncguy]

Two of the vehicles I own use some oil between changes. I switched the Galant to SuperTech 10w30 recently because it used so much and I wanted something cheap to top off with. The Trooper still gets GTX 10w30. Since the end of winter I have noticed a significant drop in the amount of oil used in both vehicles. The Mitsubishi could be explained by the switch in brands but not the Isuzu which uses the same oil it has for years. Maybe warmer weather means less oil consumption?

 

[Warstud]

Originally Posted By: brandini
"A 10w30 multigrade mineral based oil is made from a 10 weight oil and has VI improvers added to thicken the product in a 212 F engine.


I think you have that backwards.....the VI improvers are added to keep the oil from thinning the product in a 212 F engine.

 

[brandini]

Originally Posted By: Warstud
Originally Posted By: brandini
"A 10w30 multigrade mineral based oil is made from a 10 weight oil and has VI improvers added to thicken the product in a 212 F engine.


I think you have that backwards.....the VI improvers are added to keep the oil from thinning the product in a 212 F engine.

Not if it's based on a 10w

 

[Warstud]

Originally Posted By: brandini
Originally Posted By: Warstud
Originally Posted By: brandini
"A 10w30 multigrade mineral based oil is made from a 10 weight oil and has VI improvers added to thicken the product in a 212 F engine.


I think you have that backwards.....the VI improvers are added to keep the oil from thinning the product in a 212 F engine.

Not if it's based on a 10w



Check out this graph.....Nowhere in the process of the engine heating up to operating temperature does the oil thicken.

http://www.widman.biz/English/Calculators/Graph.html

 

[Gary Allan]

Yeah, but it's a perspective thing. In reality it thins less, but it is surely thicker than it would be without the VII.



I guess if you called VII an anti-thinning agent ..that would work.

 

[brandini]

Well said.