Going from conventional to Synthetic - Good or bad?

[Sevillian273]

My 4.5 has been running conventional 10w30 for 61800 miles. Ive been considering going with synthetic from now on. Other than the cost, is there ANY reason this might not be a good idea? Even if there isnt any perceivable benefit, Id still like to know that Im using the best possible oil.

[HUF]

Rotella 15W- 40 is the best all season motor oil for your car. Under normal driving conditions (no racing) you will not benefit from syntetic oil. This topic has been discussed many many times. My advice is based on the recommendation of a well known GM engineer who does not frequent this site anymore... unfortunately. He was involved in developing powertrains of many GM cars including 4.* engines.

[zentrade]

I truly do believe that synthetic is the best way to go and although upfront out of pocket is more costly, It does not take long for synthetic use to actually be cheaper to use....in my opinion that is.

The lower cost theory for me is that i don`t need to change synthetic as often as petroleum oil. Synthetic really is more resilient.

Even when i used petroleum based oil, I never believed in the 3k oil change sell that really seemed to get pushed heavily in the 80`s when quick lube joints popped up everywhere. There was a lot in it for them to get repeat business more often. I would change at 5K and no car i have ever owned suffered engine failure or damage, Its always been the car falling apart around the engine that prompted me to give up on it.

In the least You should be able to double the 3k interval with synthetic. Its great for cold weather as it flows easier at cold start to help protect your engine and it holds up under more heat better.

Less oil changes mean less pollution with less drain intervals and less dependence on crude.

I think any decent petroleum oil protects your engine. Synthetic offers the advantages i mention. To me its the cold start protection i like and the longer lasting benefits, That ends up costing me less.

[Dave S Texas]

I got my '87 DeVille in 1998 at almost the same exact odometer reading of your car. I knew the car hadn't been driven much the 5yrs previous and had no maintenance. One look in the oil-filler showed the results: lotsa gunk. I changed the oil and used Mobil1 w/Wix filter. M1 has a strong detergent package and a Wix oil-filter is the best. What I didn't know then was that syn oil did not play well with the cork oil-pan gasket the engine had. That was the only downside. The M1/Wix filter did a job on the gunk-junk. I changed the filter at 3k intervals and the oil at the 3rd filter change. I recently pulled that engine and opened the valve covers/oil pan. Except for carbon residue, it's gunk free after 35K plus miles added since I acquired the car. The GM engineers recommendation is conventional
10w-30 at 7500mi changes. Using a good filter is most important. I'll be using Pennz conventional oil and a purolator-plus filter in my new 4.1 engine. Use whichever oil you want, but using a good oil-filter is more important.

[Sevillian273]

So what does the synthetic oil do to the cork gasket? Mine is already leaking and drips down onto the crossover pipe. Also, Ive been running a Delco PF-61 filter ever since I heard so many negative things about the Fram filters; Who makes the wix filter and where can I get one? I think Ill be running Rotella 15w-40 in the spring/summer when it warms up a bit because I dont like seeing 60+ psi oil pressure when its cold out.

[Dave S Texas]

Not exactly sure, but maybe the molecules are smaller or the syn is more slippery. Neoprene gaskets are used with syn. Conventional oil is 'good' with the old-time cork gasket material. Wix filters are made by Dana Corp. O'Reilly carries Wix brand filters. I've changed to PurolatorPlus oil-filters/air-filters. Very equal to Wix, but less expensive. Delco filters aren't made by Delco anymore. Some filter company in Canada and one of the brands is Delco. I lump them into the same catagory as fram. Purolator has been making filters in NC since the '20s

[clok1966]

well my 2 cents. Somebody metioned that synts go longer, agree 100%. But they also mentioned they felt the quick lube places and the 3000 oil changes is to much. My father is a mechanic, been for a long time (retiring now) and while I never did it for a living, I do and have did all work on my cars for many years (many overhauls/rebuilds and parts swaps, am a piston head (cuz of dad I'm sure) since day 1). We have discussed engine life nowdays many times. Oil changes where a gray area up till the 70-80's really. Oil companies where saying some pretty interesting life cycles. There are several reasons 100,000 miles on a car inst the end anymore (and yes i know many of you got those older cars past 100,000). OIL- yes its better, but i also think the 3000 change cycle helps too. Synth-great stuff and I agree with its lifespan claims. manufacturing-better overall.

but with more frequent changes you get your car looked over, and they cost almost the same (other then your time to drive in and have them done... that can be annoying).

OP- i doubt it will hurt you going to Synth, the old "thought" on the matter was switching brands could losen deposits in the engine. I do not think you will see that nowdays (alot of conventinal thoughts and ideas on cars where formed in the 20-80's and have never been changed. Look up the "warm your car up before driving" thing. Oil is important to keep clean and change, very simple. What oil you use is a personal prefrence if you follow the recomended guidelines.

I subscribe to the 3000 or spring and before winter no matter what school of thought, but i have used synth and it worked well.

As for the gasket leaking problem, its doubtfull it was the synth unless you used it from day one. Synth whenit came out originaly had a differnt affect on seals that had been designed for regualr oils. This is basicly been eliminated. So nowdays its hsouldnt be a concern. Oil actualy doesnt break down, but heat (lots of it) can change its viscosity, there is one place Synth is better, it changes at a much higher temp. But any car that isnt getting overheated this wont really be an issue. here is a trivia fact: recycled Oil is used by many police and hyway patrol cars, and they use there cars much more strenous then you or me (or most of us) and they generaly go 120-150,000 before they are sold (still working) to the public.

[Sevillian273]

Well Ive bought a jug of Castrol GTX Synthetic 5w-30 and another Delco filter. In about 800 miles Ill be putting them in. Ill be sure to report back if I notice anything interesting such as my oil pan leak getting worse or any kind of lifter noise. I remember a couple years ago when I put Valvoline synthetic "blend" in my super high mileage Grand Marquis the lifter noise was so loud for some reason that I immediately drained it and switched back to conventional oil and the noise was back to normal......

[Dave S Texas]

Castrol is good oil, but I'd take that delco filter back and buy a Purolator. The very same thing happened to my Ford when I installed some Rotella syn oil. '81 F100 that I bought new. Changed oil/filter religiously at 3K intervals, except when I was running M1 syn. I thought I'd try the Rotella syn...price! My 300cid engine made terrible sounds with that stuff, so 5mi later, I recycled that oil. I've been using Max-Life in it since. It is 15% syn.

[cadillac_al]

5w-30 sounds pretty thin for Florida. Even 10-40 synthetic has better cold start flowability than 10-30 conventional. I'm not saying it will definitely cause a problem but that is some thin oil there. If the oil light doesn't flicker at idle then you will know you have a tight engine.

[Sevillian273]

I have an oil pressure guage tee'd together with my oil sensor and Ive noticed 60-70 psi at 1500rpm at 50degrees outside until it reaches operating temperature. I dont know if thats 'normal' but I dont like the idea of all that pressure on the internal seals so I figured for the colder months Id go with the 5w-30 and see if its any lower. Maybe since ill be going with synth Ill just stick with the 10w... I have about 700mi to go before I make a decision.

[Dave S Texas]

That is way too high at only 1500rpm. Tolerances are .001" and oil has to flow within that space. Either that oil is too thick, the filter clogged or some other restriction is causing such readings.....assuming the gage is accurate. Figuring 10psi/1000rpm is a safe reading. 30psi at NOT is the minimum in the FSM specs. I don't think I could wait 700mi.....

[cadillac_al]

That oil pressure is pretty high if the gauge is accurate. With that reading I'm not sure I would believe it. I guess the 5-30 would be an interesting experiment after all. What happens if you go over 1500 rpm? does the oil pressure keep going up? Maybe you shouldn't wait 700 miles.

[Sevillian273]

Let me make clear that the 'high' pressure Im experiencing is only when the engine is cold. At operating temp (around 200) the oil pressure is within range(35-50 at 1500). I didnt install the guage until around july 08 so this is the first cold season Ive had with the guage. btw, Im running Castrol 10w30 with a delco filter.

Over 1500 rpm the pressure climbs up around 70(cold) but Ive never seen it hit 80. Replacing the filter from a Fram Tough Guard to a Delco was the first thing I did but to no avail... I think I will make a chart with the pressure at different circumstances ie: engine temp, rpm, and ambient temp. Ive heard so many good things about this Rotella T and I want to start using it but with these high pressures Im afraid to go to 15w....

[cadillac_al]

That's nice pressure. 70 max at cold isn't a problem. Your car only has 60,000+ miles on it so it must be pretty tight. I would be very curious if that 5-30 lowered the oil pressure any. You shouldn't have to worry about low oil pressure. I put 5-30 in mine last winter and the oil light started flickering so I had to drain it out and go back to 15-40 but mine has 190,000 on it. Let us know how it works out for you. I always liked those old 90 Sevilles, it sounds like you have a nice one.