Castrol ATF

Question for you pros…

My mechanic who I trust wants to use a transmission fluid made by Castrol in my Accord that can supposedly be used in lieu of Honda Z-1 permanently.

The transmission fluid is full of Z-1 so my questions are:

1. Is it ok to let him use this fluid in my vehicle?

2. If the answer to #1 is yes, then will mixing this with Z-1 create issues? (He will just drain and refill the fluid, which of course does not remove all of the old fluid).

Thanks in advance.

Correction to Line 4 The transmission is full of Z-1

Why can’t we edit our OPs?

Does the Castrol ATF say that it is compatible with Honda transmissions?

I put Valvoline MaxLife ATF in my Honda.


I am no pro, but I own and drive Hondas. I would insist on the Honda brand fluid.

What does your owner’s manual say about this issue?

Honda doesn’t refine and manufacture their own fluid. As long as the additives in the ATF meet the same requirements, I’d rather not pay Honda’s inflated prices.

As much a believer as I am about oil brands being pretty interchangeable, I’d go with the Honda Z-1 here. Just too many cases of Honda ATs being troublesome.

I’ve gotten chastised a bit for this on other threads - but I don’t trust the multi-spec fluids. They are engineered to meet lots of different specs so they will minimally meet them all - but are all of the specs really optimized? Well, they can’t be optimized for your exact specs since some things are bent to accommodate other things. I’ve always thought of them as probably “good enough” but not “optimum.” The exact spec will generally cost a bit more but to me it is cheap in comparison to messing with the health of the transmission.

You will, of course, get varying opinions.

FYI: with some internet searching you can find the exact Honda specs and then you can find them for any fluid on the market to compare.

I too am one that believes it’s worth the extra few bucks to use only the exact tranny fluid specified in the owner’s manual.

Trannys are too expensive to risk. Tranny fluid performs functions beyond just a lubricant. It’s a hydraulic fluid, a cooling fluid, and a seal preservative. It’s also a major component of the torque converter, which is a fluid-transfer device that uses the fluid to transfer torque and to absorb energy when stopped. If it’s not exactly correct you risk a very expensive problem.

First, I know Honda doesn’t make the fluid. Second, I wouldn’t take Castrol’s word for it. Third, you can buy Honda OEM products online as cheaply as you can buy Castrol’s product from a store, so you aren’t saving any money. You don’t have to pay inflated prices by buying OEM Honda products at the dealership.

For all we know, Castrol might be the maker of Honda’s Z-1 fluid. If that is the case, I still wouldn’t assume the products are made to the same specifications.

Knowing all this, why would you take the risk? What do you expect to gain? You won’t save money and the Castrol product might not be as good as advertised.

I will ask again, what does the owner’s manual say? If the owner’s manual lists the specifications the fluid must meet, and this product meets those specifications, go for it. If you are just going by Castrol’s claims, good luck. Those claims might be a rare case of truth in advertising, but I wouldn’t bet on it with nothing to gain.

Jeffmw05, do an internet search for “Honda OEM parts.” The last time I ordered OEM parts online, I got them for much less than I would have paid at the dealership.

Thanks for the input. I too am more comfortable with the Z-1. The dealer quoted me $67 to drain and fill the trans with OEM fluid and my mechanic wanted $50 or so. I think the $17 premium may be worth it. Thanks again.

Honda’s, much like Chryslers are very picky about what you put in them. You need to stay with the Honda fluid.


Hey transman,

Thanks for checking out this thread.

That’s exactly what I needed to know thanks.

Hondas are FAMOUS for having fragile, short-lived transmissions. They need all the help they can get. Then, if your transmission blows, you can’t blame it on the fluid…

This one has lasted 11 years / 145k so far. If I get 200k out of it knocks on wood i’ll feel that I got my $'s worth out of the car.

A lot of good Honda Z-1 did for Odyssey, Accord, and Acura TL owners. For all we know these transmissions would have lasted longer on other tranny fluid.

Honda says to use Honda brake fluid, Honda power steering fluid, Honda coolant, Honda oil. Should every Honda owner only use Honda fluids and Honda original parts too?

Owner’s manual Specifies Z-1, or a generic brand only as an emergency top off.

No, of course not.

Aren’t there other causes of transmission failure other than the fluid? Why are you so quick to blame the fluid for what was probably a mechanical failure based on a bad design?

I don’t use Honda’s fluids for everything, but if I had a Honda automatic transmission, you can bet I would want to eliminate the fluid as a contributing factor of failure, especially if I wanted to protect my warranty.

I don’t use Honda manual transmission fluid, or Honda brand power steering fluid (I do use PS fluid made for use in Hondas, but another brand), Honda brake/clutch fluid, Honda oil, or Honda motorcycle oil. I do, however, use Honda coolant and brake fluid on my motorcycles. Nobody here is saying you should only use Honda’s fluids and parts, but there are some occasions when it just makes sense, and this is one of them.

I’m not blaming the tranny fluid but I don’t know of any scientific evidence that Honda’s Z-1 is any better than other Honda compatible ATF. Just like Honda power steering fluid isn’t necessarily better than other power steering fluid.

Does anybody have any evidence or scientific proof that Honda Z-1 the best?

Well transman is an independent practitioner and therefore has no reason to boost Honda’s profits. If he recommends the Z1, i’m taking that advice to the bank.