Are the genuine really worth the higher cost than aftermarket? If it the car body parts, I would say yes, but if something mechanical or any fluid or oil, not so sure… I would like to know your experience and opinions to help me save money and trouble.
You really can’t generalize that much. Body parts are nick named sorta fit parts because there may be quite a little re-fitting that may be required. Plus the gauge of the steel and rust prevention. Some after market parts are made by the same vendors that the big boys use but may or may not be made to the same specs. Would I buy Walmart brand oil though instead of Mobil? No.
Generally nearly every fluid is available on the aftermarket. There are exceptions like Honda manual transmission fluid and some of the more specific coolants like Ford spec gold or Toyota. There are universal coolants but you change it so infrequently, why risk incompatibility? GM transfer case fluid is another specialty fluid but Napa carries it as well as GM. Brake fluids are as good as factory or better IF they are the same grade, Dot 3 or 4 or 5.1. Dot 5 is silicone based and isn’t standard on anything but Harley Davidson motorcycles, I believe.
There are cheap, good, better and great motor oils on the market. Take note of the API rating your car needs and meet or beat that. Avoid cheap oil, IMHO. Buy the best you can stand to pay for and change often. It is cheaper than an engine rebuild.
For fluids sometimes it matters, most of the time it doesn’t, Some cars have transmissions that have pretty exacting requirements and it’s best to use the manufacturer’s exact fluid. But for things like motor oil, you’re fine to use whatever meets the manufacturer’s specs. No car manufacturer actually makes their oil motor oil, most of the time it’s just rebranded or slightly reformulated versions of common brands of motor oil.
I would say you have to decide on a one by one basis, because there is so much variation in the industry. IF you buy a good brand of car, the amount you need to buy will be so small it won’t hurt to buy the good stuff.
I do have a non-popular view of rebuilt parts, though. I have been driving since around 1960 and have never had a rebuilt part last over 2 years, even when the original part lasted for a very long time.
On my 2002 Sienna, which I had to park a year ago with 220,000 miles I only used new Toyota parts. It was not repair free as some report, but there weren’t a lot of repairs. The reason I parked a perfectly good car was because of a change in Mexico car import laws, or that car would be the last one I ever bought.
I drove the car for many months at a time into Mexico. But, I was able to do all repairs back in Texas, except the battery went bad without warning. That is, even if I had a problem the car could be driven 850 miles to the border, except the bad battery. Well, a lot of flat tires, but that is not on Toyota.
edited: said part when I meant park, sorry
In the case of coolant and/or tranny fluid, I prefer to use OEM fluids. It just isn’t worth the risk to save a couple of bucks every 5 years (or whatever).
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Please be aware that NO modern MFR “makes” oil or tranny fluid; they sub-contract it out to a “name” lubricant company. With a little digging, you can find out who it is.
Oil that “meets XYZ specifications” is equivalent to “XYZ oil” IF you trust the company making the claim. I tend to trust the company…no multi-billion dollar company is going to risk “inventing” credentials.
I needed differential fluid as at 160k I thought it was time to change it, dealer was $32, I bought it at the dealer, whatever parts was less, including an $8 tube of antislip whatever, the $4 I might have saved paled in comparison to being sure of the proper part for the proper job in my book. Spent the extra bucks to get dealer transfer case fluid also, just to be sure I was getting the right stuff.
There is an awesome site that does oil analysis and post their finding. I can’t find the site and I didn’t bookmark it but basically any oil from a reputable vendor (not gas stations) is good oil.
As far as parts go many people use after market parts even the repair shops. While some parts from certain vendors don’t last as long the parts that cost more in most cases last longer. Check Napa gaskets vs auto zone or advanced.
Also stick with brand names if possible. Compare Wagner brake pads vs house brands.
I think it depends, and often depends on things we buyers have no control or knowledge over.
For example, I have one car which has a known problem with the oil pressure sensor. The OEM tends to leak early in its lifetime and require replacement. So this might be a good candidate for going aftermarket.
But when I bought one from a large auto chain store, it turned out to be slightly defective out of the box. It would occasionally go off, which left me wondering if something else was going on. After puzzling for about a year, I finally bought another from the same chain, but of a slightly ‘higher grade’ because they warranty it for life. It no longer goes off (although that might mean it doesn’t work at all 
) and things have been fine for a few years now.
Many of those parts are EXACTLY the same parts as the cheaper ones. they are just warranted longer. It is a bit of a scam since the labor is not covered and the likelihood that you will still own the car when it fails is small.
Blackstone labs is the place I used for oil analysis. You order a kit then send it in with your sample and somewhere around $25. I did it once just to see after 100,000 miles. No problems, no wear, big deal. Nothing I didn’t know but did it anyway.
On my posi-traction rear end, I would get the chattering clutches even after the first 20,000 miles. So I used the GM rear end fluid and their whale oil supplement to stop the chatter. After that I’d do the regular rear end fluid changes and use only the GM stuff. Who knows who actually made it but it wasn’t that expensive.
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You’re probably correct, and so I had ‘higher grade’ in quotes.
OTOH, the numbers/markings were different on the sensor, so at least that’s different.
Bingo! (Sorry.)
Yes, and let me emphasize that the lab test, I am talking for motor oil now, I have no experience with other fluids, doesn’t just tell you if the oil was bad. It can spot all sorts of motor problems. Blow-by; coolant contamination; bad rings; valve train and cam problems; bearing wear; it’s like the best motor inspection you can imagine.
I’ll go further and say no manufacturer makes AN FLUIDS. They are all made for them by some oil or chemical company.
Some fluids like tranny and cooling fluids are made to exacting manufacturer specifications.
I used to go by the theory that “parts is parts”. Back in 1964 the.fuel pump started leaking on my 1954 Buick. An AC OEM reconditioned pump was $15.95 at NAPA and a new pump at Western Auto was $8.75, I went the Western Auto route. I was a poor graduate student only making $200 a month back then. The Western Auto pump was still working a couple of years later when I sold the car. However, I had terrible luck with Western Auto spark plugs in the Buick. The plugs had two electrodes and kept fouling out. I put in the correct AC 44 plugs and had no more problems. I found that AC 44 plugs were cross referenced with Champion J8 which were used in my lawnmower. I cleaned up the Western Auto plugs for the mower and they didn’t work there either.
My 2006 Chevrolet Uplander came with Dexcool coolant. I replaced the Dexcool with green antifreeze and had no problems.
I have 5 GM cars running on Dex-Cool. I always replace my Dex-Cool with Dex-Cool and have never had any problems. It always looks brand new.
It needlessly gets a bad rap. I think it started with very early versions of the coolant, somewhat problematic. Then it was re-formulated, years ago, and Voila! No problems!
On the other hand, I had problems with the factory green stuff in my Dodge Caravan. It didn’t go very long without gunking. I switched to the yellow universal coolant and Voila! It stays as fresh as Rocky Mountain spring water!
CSA 
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@common_sense_answer. My son now has the Uplander. It has traveled about 200,000 miles and has never had as water pump, intake manifold gasket, heater core problem or.any problem that could be related to the type of coolant in the system. Now it may have done as well on Dexcool.My independent shop recommended switching away from Dexcool when the coolant was due to be changed.
When money was tight and I did my own work,I used house brand coolant and house brand oil that met the specs for my car and had no problems. I even would substitute a major brand spark plug that was on sale for the original equipment plug. I"ve used Autolite.plugs in place of AC and experienced no problems. This was back when we did 15000 mile tuneups. The only problem I ever had was with the Western Auto dual tip plugs.
When I had my coolant flush done the shop I patronize went went with peak global, I did not ask why but trust their judgement.
@Barkydog Years ago, for summer coolant, I switched from Budweiser to Billy Beer that was being closed out at 99¢ a six-pack. The switch caused no harmful effects. I am still going strong at 75,.
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