High mileage 4 cylinder. The owner's manual calls for 5w/30 if the outside temp isn't going to exceed 100 deg F before next oil change. Does it really make any difference if I jump up to 10w30?
Synthetic is out-too many miles IMO.

My oil cap says something about 5W oil but I've always used 10W30 here in Fl. PS and I thought I was the only one still up.

on my V6 i run 10W-40, and im thinking of going to 20w-50 this spring

Oil??

I use wd-40

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Failing to prepare - Is preparing to fail....

I didn't remember if my 2m4 liked 5W30 or 10W30 (been awhile, it had been sitting until now). I know the V6 recommends 5W30, and I thought we used to put 10W30 in the 2m4 so I gave it a shot and oil pressure is just right, here in CA with 50-60 degree weather. I figure 5W30 for the V6 and 10W30 for the 4

5w-30 is like friggin water ...the only oil i ever use in my car's is 10w-30

My 86 GT had 5W-30 in it when I bought it. 136K miles. The idle oil pressure was too low to suit me. I went to 10W-30 in the winter and 10W-40 in summer. Maybe its just an illusion but I like to see the oil pressure above the red line.

An engine gets most of it's wear on cold startup because it doesn't have that very thin film of oil between moving parts.If you go with an oil that is too heavy it prolongs the amount of time it takes to get that oil where it belongs.Going from 5w to 10 w is probably ok on a high mileage engine,but,I wouldn't go any higher on the lower number because of the extra time needed to get the oil throughout the engine where it is needed.It would only accelerate wear.

I run 5W50 synthetic.

Like stated above, the 5Wxx is better on the engines for cold start.

Anything with xxWxx is an engineered oil formula to help stabilize the thickness (viscosity) of oil over a large temperature range. There are viscosity graphs that measure this thickness from something like 0 to 100 degrees. All oils are much, much thicker cold than when hot.

The first # refers to the comparable cold viscosity. Which means when cold the oil will have the comparable viscosity of 5w (one of the thinnest options for cold start). The second # refers to the comparable viscosity of the oil at a high temperature. So when hot the oil will behave more like the second number.

Most people notice that when they start their car up the oil pressure gauge gets pegged or reads 50+ PSI (even with 5 weight). But at a hot idle the oil pressure drops to 20 to 30 psi. This is due to the oil loosing its viscosity as it warms up.

The 5 weight cold is still thicker (has more viscosity) than 30 weight (or 40, or 50) at a hot idle.

I run the 5w50 to keep the oil viscosity more constant (but it still drops).

quote Originally posted by hugh: An engine gets most of it's wear on cold startup because it doesn't have that very thin film of oil between moving parts.If you go with an oil that is too heavy it prolongs the amount of time it takes to get that oil where it belongs.Going from 5w to 10 w is probably ok on a high mileage engine,but,I wouldn't go any higher on the lower number because of the extra time needed to get the oil throughout the engine where it is needed.It would only accelerate wear.

I can back this up with real experience. I accidently grabbed 10W30 off the shelf for my last oil change and didn't notice until I was throwing away the bottles. I usually use 5W30 in this newly rebuilt engine. I noticed two things immediatley. 1) It has to crank a half second longer to start and 2) for the first second of running I can hear the lifters rattle.
Use the manufacturers recommended oil. They recommend it for a reason. (Also pay attention when shopping at WalMart )

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84 Sport Coupe
87 GT 5 Spd

The car maker say 5w-30 because it will cover all climates and they are on the safe side. but if you live in a warmer climate where it very seldom gets below 60 degrees, then I would use the thicker oil. For example, Hawaii where it maintains a average tenp of 72 degrees, you do not need thin oil. just my thoughts
Don

Thanks to all. +s.
The car came into my possession with 5w/30 used it's entire life according to the previous owner, so that's what I used when I changed it, but it spent it's 1st 20 yrs in the upper to mid-atlantic states--much cooler than west Texas. Getting ready to change it again and prepare for the onslaught of high temps here. For the miles, 114,xxx, it has suprisingly little blowby tho I really haven't done a compression check. It does have a slight puff of smoke on start-up indicating bad valve stem seals. I think I'll stick with 5w/30 this time and try 10w/30 next time or right before I take it on the road to San Antonio in mid April.

In a 5W30 multiblend oil the first number is the base stock of the oil. The secound number is what the oil will thicken to with heat. The oil has a plastic polymer chain that in cold conditions is in a ball and when heated expands into a longer chain, thus thickening the oil. So for high heat applications you want a higher secound number. I always run 10W40 in Texas because of the heat, even in the winter, because it doesn't get too cold. 5W30 would be right for mid-US, but is to thin for west Texas. Here are some links that explain it in more detail than I have given you.

http://auto.howstuffworks.com/question164.htm How oil works.

http://www.tuninglinx.com/html/a_oil_clm.html How to select oil wt by outside temps.

FYI-You can not run multigrade oil in an aircooled engine because the high heat in the heads frys the polymer and you end up with base stock which is too thin for the engine.

I know very few people out here that run xx/40 wt oil-even in mid summer, unless it's in industrial engines. I don't doubt what you are saying is true, but i have asked around & know what others here are using.

This is the 2nd Fiero we have acquired, and I ran 5w/30 or 10/30 in Jane's 84 for 8 years, before doing an engine replacement at 155,000 miles and went to Mobil1 with it.

I'll have to think about it.

Thanks for the heads up on the air cooled engine info. If I ever put a Deutz or Perkins in my 84 I'll use straight wt oil.

quote Originally posted by webbee: FYI-You can not run multigrade oil in an aircooled engine because the high heat in the heads frys the polymer and you end up with base stock which is too thin for the engine.

Sorry, but that's just not true! Porsche says it's not true for their air-cooled 911-series engines. Lycoming and Continental say it's not true for their air-cooled aircraft engines. Every motorcycle manufacturer that recommends multiweight oil says it's not true for their air-cooled motors either.

Most "air-cooled" engines are actually air and oil cooled. In the 911 engine, about 30% of the cooling (i.e. heat rejection) is through the oil. I agree that air-cooled engines tend to run the oil at higher average temperatures and thus may make higher demands on the oil, but the peak temperature the oil sees is usually on the bottoms of the piston crowns, and that peak temperature is generally independent of air vs. water cooling.

[This message has been edited by Marvin McInnis (edited 02-28-2005).]

The manual for my Craftsman lawn mower says 30 wt in the summer. Do not use multiviscosity oils in the summer. 0 to 60 in 2 hours and 13 minutes. Down hill. Not quite a Porsche I'll have to admit.

quote Originally posted by Marvin McInnis: Sorry, but that's just not true! Porsche says it's not true for their air-cooled 911-series engines. Lycoming and Continental say it's not true for their air-cooled aircraft engines. Every motorcycle manufacturer that recommends multiweight oil says it's not true for their air-cooled motors either. Most "air-cooled" engines are actually air and oil cooled. In the 911 engine, about 30% of the cooling (i.e. heat rejection) is through the oil. I agree that air-cooled engines tend to run the oil at higher average temperatures and thus may make higher demands on the oil, but the peak temperature the oil sees is usually on the bottoms of the piston crowns, and that peak temperature is generally independent of air vs. water cooling.

Another car I have is a 1974 VW bus, which I have owned for 23 years. I have rebuilt the engine at least 4 times in it's 500K+ miles. Bus engines usually don't live more than 90K because of poor cooling in the engine compartment. I ruined my first VW engine running multigrade. Hot VW's ran extensive testing on single vs multiweight oil and it was found that the head temps fried the polymer. This flies in the face of VW's recommendation's to run multigrade. It is possible that polymer has been improved and now doesn't fry. That being said, I still won't run multigrade in an air cooled engine, especially if it is subjected to operation in extreme heat. Especially if you want the engine to hold up for it's full service life. Air cooled is a different beast...

Aircraft and motorcycle engines are direct air stream cooled. The head temps probably don't run as high because of better cooling. I don't know about Porsche engines other than I have a 914 in the bus. Believe me, it's all about head temps.

5w30 is worthless. As soon as you get the car warmed up, the oil pressure goes straight to hell. I switched to synthetic last oil change. I went with 10w30 Castrol synthetic. I'm gonna step it up a bit next change. Still gets down to 40ish PSI, and that ain't cool.

www.bobistheoilguy.com

The site with all the answers to your oil questions!

Synthetic?...Now that's another thread, and it is here:

https://www.fiero.nl/forum/Forum2/HTML/055214.html