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Factory change in oil viscosity

Does anyone know why Mercury changed the oil viscosity recommendation in the 4.3 liter engine from 5w-30 to 5w-20. My engine seized up at about 115,000, I heard it was because the engine tolerences on the 4.3 liter were too close for the 5w-30 oil.

I doubt that. The change was likely to increase gas milage slightly. What year Cougar?

1996 Mercury Cougar

OK - do you mean the 4.6l v8?

Yes I mistyped, it was the 4.6.

EXTREMELY UNLIKELY that 5W30 was the cause of your engine seizing up!! In 1996 engine tolerances were very loose still, and almost every car on the road used 5W30 oil. In tropical countries they put 20W50 in those engines!! Most engines could use 5W30 or 10W30 depending on climate.

Engines seize up mostly through 1) lack of oil in the crankcase, 2) plugged oil galleries due to sludging or no oil changes, 3) failure of oil pump, 4) other causes preventing oil from being circulated to the areas needed, 5) lack of coolant causing the engine to overheat. I suspect your engine suffered one or more of the above failures.

The change to 5W20 was driven simply by trying to meet the Corporate Average Fuel Economy (CAFE) standards, and escape another $40 million fine for not meeting it. Ford concentrated on large, profitable vehicles and almost abandoned mid and small cars.

They pulled the same stunt on Mazda when they owned it. my son’s 2004 Mazda 3 calls for 5W20 oil, but he puts in 0W30 full synthetic. After 70,000 miles the engine is still in like new condition.

In 2007 I had a rented new Ford Explorer; it called for 5W30 for one engine and 5W20 for a different engine. The reason here being that 5W20 in the unsuitable engine would cause EXCESSIVE OIL CONSUMPTION due to the large clearances!

Who did you “hear” this information from?

I have '98 Crown Vic with the same engine (millions of these engines have been built and they usually go at least 200,000 miles without any problems…) and I have used 15W -40 fleet oil in it during the summer months without any problems…This car has 160,000 miles on it.

Who knows why the OP’s engine failed, but it wasn’t because he used 5W-30 motor oil…

Your engine didn’t seize up because you were using 5W-30 oil. It’s true Ford issued a TSB saying that the recommended oil for some engines is now 5W-20. But sticking to 5W-30 won’t hurt anything, if that were the case there would’ve been a lot of seized 4.6Ls.

I’ll also add this. There’s no reason not to use 5W-20 oil when it’s recommended. Alot of people say that it’s too thin, or it’ll breakdown under demanding circumstances ,yadda yadda yadda. The truth is there hasn’t been a single engine failure attributed to the use of 5W-20 vs. a heavier weight. Also 5W-20 will get circulated around the engine more quickly than a heavier oil will upon startup, which is when most engine wear happens in the first place.

There is a difference between an oil “causing failure” and causing faster engine wear. To get an engine to fail with 5W20 dino oil you would have to severely load it or overheat it.

However, increased engine wear is common if the vehicle with 5W20 is driver at high speed for an extended period or heavily loaded. That’s why German cars use 0W40 or 5W40 (20W50 in the past), since you can drive from Munich to Hamburg at 100 mph non-stop. A 5W20 oil just doesn’t cut it under those conditions!

The “fast circulation” part is the first number, if its is 5W, then any 5W oil will circulate at the same rate; that’s also why I use 0W30 full synthetic in very cold weather; it circulates even faster since it has a Pour Point of -45C.

You can find all this info in a primer text on engine oils.

German cars don’t have to meet CAFE standards in Europe, so they can specify whatever oil IS BEST FOR THE CAR!

Show me a single engine that’s worn out due to 5W-20 oil. I’ve taken my car (Mustang GT w/supercharger) to several track days at VIR. Alot of full throttle use, and speeds approaching 140 MPH. It’s a hell of alot more demanding on the engine than cruising at 100 MPH for a few hours. The car has about 100k on it now, runs fine, compression is well within spec,etc. I use 5W-20, usually Pennzoil Platinum. My opinion and the general consensus of BTOG users is that 5W-20 provides all the protection you’ll ever need.

I think that engine engineers laugh every time they see the “closer tolerances” in conjunction with oil recommendations. Does anyone have evidence of such closer tolerances between 1990 and 2010?

A quarter-mile run demands very little from the oil…It’s hour after hour at 80 mph in 100 degree heat that turns 5w-20 into water and cam lobes into residue…

There’s no tighter clearances …the tolerances are closer to design spec than they’ve ever been due to advances in machining and materials.

Millions upon millions of engines have been using 20 grade oils for decades. From the later 70’s on forward. They typically sheared back to their 20 weight base stock origin. MILLIONS UPON MILLIONS. The only thing Ford did was bring a 5w-20 to the market so that they could take advantage of it from the get go and use it for certification. They already had the viability in the bag on common pushrod engines. Something like the modular was a no-brainer …as well as just about everything else. The exception being the Cologne engine (4.0 SOHC) where they conceded that the oil pump would need modification to have it work.

You’ll note that Ford allowed time for the market to catch up in extending its service length …but it turned out to be a painless transition.

Millions and millions of engines have been using 10-40 motor oil for decades…

The only engines that I know of that are really seem sensitive to oil viscosity are air cooled lawnmower engines. My lawnmower manual requires straight 30 weight in the summer, but has different specifications for winter (I don’t know who would use a lawnmower in the winter). My neighbor threw a rod in a lawnmower engine that he had just filled with 10W-30 oil. In the interest of science and because I hate to mow yard, I may try the 10W-30 in my mower to see what happens.

I have a generator with an 8 horsepower air cooled engine. Its manual recommends 30 weight for the summer, but if the generator is going to be used in different climate conditions, 5W-30 synthetic oil is recommended. Since I need the generator in the winter to keep the furnace controls and blower going in the winter, and to keep the freezer going in the summer (my power comes from a high voltage underground feeder line that seems to short out in wet weather. Sometimes it takes the power company a couple days to get to the problem) I use the synthetic oil.

If you switch your Mercury to 5W-30 it will probably go 200,001 miles instead of the 200,000 miles it will run on the 5W-20 oil. My guess is that Ford issued this bulletin because, as others have said, this may raise the corporate fleet average mpg in the newer cars. By recommending the 5W-20 for older cars, the dealers are happy because they only have to buy bulk oil in one viscosity.

FoDaddy; you can do this forum a great favor in convincing us that standard 5W20 is good for ALL driving conditions, even in Germany.

Since you are not likely to take your Mustang out on the Autobahn at 100 mph, or pull a heavy trailer with it, please do the following:

Take a July holiday in New Mexico, where, I understand, you can go as fast as you want. Fill the Mustang with off-the-shelf 5W20 dino oil , load up the car and drive 450 miles (the distance from Munich to Hamburg) at 100-110 mph with the A/C on.

I will compensate you for any oil used during this trip, but not a blown engine.

A friend of mine, who is an oil specialist, helped a Corvette racing team win with 0W20 SYNTHETIC oil since it greatly reduced internal friction and gave an additional 5 mph top speed. He agreed that this was done to WIN RACES, not to MAXIMIZE ENGINE LIFE!

Millions and millions of engines have been using 10-40 motor oil for decades… Not as a domestic OEM recommendation. 5w-30 for a very very long time. 5w-20 for most from shortly after 2002 when Ford made the stuff widely available. Even Vette’s spec’d 5w-30 …3/4 ton SBC’s pickups …you name it.

When millions and millions of cars used 10W40 engine oil, we were used to overhauls at 120,000-150,000 miles, not 350,000+ as often now. Cold starts with the 10W40 caused severe engine wear, offsetting the benefits of the higher viscosity at warmed up highway speeds.

The consistency of the viscosity (or lack thereof) was revealed in a 1984 Consumer Reports test on oils which found that the oils for sale then were very often not able to hold their viscosity at increased tempertures. Texaco was the worst performer at that time.

Since those bad old days when it made some sense to use 10W40, the testing and quality standards have improved immensely, and the most recent CR tests a few years ago showed all brand name oils staying within the viscosity range specified. So a 5W30 oil will suffice for most driving conditions. However, if you live in Texas and tow a trailer in the summer, I would still use 15W40 dino oil or 5W40 synthetic.

That I can accept easily, but do engineer laugh when they see that reason for using “thinner” oil, or do they groan and roll their eyes?

Well I’m A believer in the 5w20 oil. My 2002 Cougar 2.5 V6 has over 225000 mi on it and runs great never had to add oil between changes.I get Motocraft 5w20 synthetic blend at Walmart for $11.50 5qt jugs and a Walmart brand oil filter for $2.35 so their filters must be good to. I change oil every 5000 mi. when the maintenance light comes on.So as you can see this car dont sit around it travels I95 everyday at 75 to 80mph in MD we also get plenty of 90 to 100 degree days to.