: Synthetic Motor Oil: Take a look.

02-14-06, 07:30 PM
Hello everyone. I own a 1997 Catera with 94,000 miles on it. Everything I've read about synthetic motor oil seems to be pointing to good but what has me worried is the high mileage on the car. I read that synthetics break down old non-synthetic motor oil that may have sealed cracks and leaks throughout the life of the engine so far.

So would it be a bad idea to convert this high mileage catera to fully synthetic motor oil? Or do you think it'll be alright? Need some input on this because I'd like to change the oil soon and this will be my determining factor.

Thanks. :burn:

02-15-06, 07:43 AM
A synthetic won't break down anything. It's not a solvent. I mean you could seriously mix the two if you wanted. You would be throwing your money into the garbage if you did, because it would nullify most of the benefit of synthetic oil (longer change interval, better protection). It wouldn't hurt anything though. These aren't 1960s semi-experimental synthetics which turn to putty or solidify when mixed. All current synthetics play just fine with regular oil. Also, idiots like to say synthetics will leak faster, or "slide around rings" and be burned faster. The ability of a fluid to get through a given gap is determined by its viscosity, not its lubricating properties (more "slippery" does not mean more leak). If 5w30 natural oil will not leak through a gap or get around rings, neither will the synthetic equivalent.

Just make sure you use a REAL Synthetic. Castrol and Pennzoil are NOT real. They are made principally of hydrocracked group 3 base oils - natural oils pure enough to be almost crystal clear (until additives are added), but they still suffer from high temperature thermal breakdown. Real synthetics have no natural base and are either esters based (Redline) or Polyalphaolefin based (Mobil1, Amsoil, Valvoline Synpower, Esso).

Remember, oil is changed because it, more specifically the viscosity agents in it, break down through heat. Oil does not get dirty, any dirt carried would be picked up by the filter. If the filter wasn't that effective in picking up dirt, 3000 miles would be an eternity, you might as well take fine sand paper to the bearing surfaces in the engine. With synthetics, the only problem is depletion of the additives. Breakdown is so small you can write it off. Mobil1 15000 mile extended synthetic is good for it. Trust me, I know. I regular have "oil analysis" done on my car. There are rarely even trace amounts of wear metals in the oil, after usually around 6000 with the Cadillac and 10000 with the BMW.

Incidentally, It isn't a one or the other type of thing concerning protection vs. extended oil change intervals. Synthetic oil if you were running it to 15000 miles would still be protecting you better at 15000 than regular mineral oils at 3000. Wow, hmm?

I just love hearing these old school monkey mechanics tell people lies like that once you use synthetic you can never change back. Telling them it will burn more. Telling them oil will leak more. (Actually synthetics usually have more seal conditioners in them and will cause it to leak less - but you didn't hear this from me.) The only thing that bothers me more than 3000 mile oil changes in good conditions is misunderstanding synthetics.

Read your manual. Some cars require synthetic. I almost bought an Audi that requires it. The BMW strongly recommends it, says 5000 miles with regular, up to 15000 miles with synthetic. A Catera probably tells you when to change the oil. I hope it can be set for synthetic, or you keep track yourself. DO NOT extend oil change intervals beyond 5000 miles if you have replaced your thermostat with a cooler design. The factory thermostat will allow the engine to warm to a level that will remove water condensation from the oil. A 180 degree thermostat will not always. The same applies if you have a large aftermarket oil cooler.

Remember, in the winter, synthetic is the way to go because it offers better cold weather performance. It circulates faster on a cold startup because it thickens less in extreme cold. (put a bottle in the freezer of synthetic 10w30 and of natural 5w30. See which is thicker to shake or pour after a night) This also decreases load on your battery (which is already not in a good mood in the cold) and starter because your oil pump does not have to move molasses.

A last thought: Get a GOOD oil filter. K&N oil filters are junk. Use ACDelco or Mobil1. I have personally cut them open before. The K&N is seriously a lousy design, looks to be prone to collapsing when full, which causes unfiltered oil to circulate, as the release valve will open to prevent starving your engine for oil.

02-15-06, 02:45 PM
Thank you for the much needed information. I already have a case of 10w30 Mobile 1 Extended and a Mobile 1 Extended filter. I just wanted to make sure I wasnt going to do any harm by switching the car over to synthetics and it's clear from your reply that there is nothing to worry about. Thanks a lot!

02-15-06, 03:47 PM
Hey zorb, Can I put royal purple in my 1980 cadillac coupe deville?

It has 86,000 miles on it and I havent noticed any leaks.

02-15-06, 07:46 PM
I don't see how it would hurt...

I don't know anything specific to Royal Purple.I have a friend who loves it, I'm kind of torn between Mobil1 and Redline myself, after having personally almost rebuilt a GM 4.3 V6 run on Mobil1. After taking apart partially, I took it apart no further, instead just replaced the bent pushrod. Very little wear at 280K miles. Just don't go by any test on Royal Purple's site. I think their "Other Synthetic" must be Castrol or something. Mobil1, Redline, and Amsoil all offer significantly better performance in oxidation than regular oils.

02-15-06, 08:05 PM
Not to undermind anyones post but I have had a personal expierence with switching to synthetic oil in a high milage catera.

Bought at 106,000 miles switched to mobil extened performance and the next week leaking cam coverer gaskets. Although these gaskets leaking is a know problem i have to believe that the sythetic oil had something to do with it. But I had the gaskets replaced for around $350 and contine to use sythetic.

Yes you might develop a leak but then again you may not but the benefits of sythetic are worth the cost of replacement of two gaskets that are know to fail.

02-16-06, 04:38 AM
Interesting. Mobil1 slowed down a case half seal leak on a 1994 Deville Concours I know.

02-16-06, 03:13 PM
No worries there I just replaced those gaskets.

Actually the left side gasket failed because I installed it improperly. I had to pull over and add 3 quarts of oil to my engine. I removed all the parts necessary to install the gasket today and I am going to re-install the left side gasket tomorrow. This time I'll make sure it fits securly in place.

What was happening was a lot of white smoke was emitting from the left side of the engine and when I brought it into the shop and got a light down there I could see burnt oil on the exhaust manifold so I put two and two together (when I installed the left side it didnt quite sit right) and realized it must have been the gasket.