Hmm thanks for the info. I currently see about 38 tops at high RPM. In general, when the oil is hot, from 3000-7000 RPM I only see 40. It flatlines at 38psi. My oil pump is the part number mz-bp4w-14-100a. I think that is the pre-99 pump? Anyways, this pressure seems a bit low. I have no oil cooler. What are your thoughts?

I think its probably ok, but its not optimal.

Did you do anything different with engine clearances/ relief valve or anything you can imagine to change oil pressure?

The simple things that change oil pressure the most have been viscosity, oil filter brand, and outside temperature(viscosity again basically). You could try upping the viscosity for one oil change to see if your oil pressure goes up with it. If it doesn't then its the relief valve. If it does go up then it could be a flow limitation(leakage or pump is too small).

The catalog is still bugging me.

Looking over the history of the oil pump, I'm seeing a lot of different part numbers over the years. It's not uncommon for mazda to change P/Ns on something fit-form-function compatible, though they usually denote this with a suffix letter change, rather than a number change.


There's at least one functional difference I can think of between the longnose 1.6 / early 1.8 NA and the '99: the mounting point for the crank sensor. I don't know whether the '96-'97 crank sensor were mounted in the same way as the NB ones, but from '99 onward, they screwed into a threaded fitting on the oil pump that the 1.6 oil pumps don't have.

I realize that it's not the most accurate dataset, however when I do a search on aftermarket oil pumps for various years in the RockAuto catalog, I see one set of pumps listed as compatible with '94-'97, and a second pump listed for '99-'00. (They have no pumps listed for any of the 1.6 engines, or for '01 and later.)


Going to the Mazda catalog gives me a slightly different dataset. I'll focus on comparing three different parts here.

For '91-'92, the oil pump as an assembly went through a major revision at VIN -0910. After that, the whole assembly is B6S8-14-100C, the inner gear is B6S7-14-132, and the outer gear is B6S7-14-141.

For '94, the assembly went through a major revision at VIN -4301. The major change was the oil control plunger. Prior to this change, the assembly was B6S8-14-100F, and afterwards it was B6BF-14-100A. The fact that the prefix changed (B6BF to B6S8) suggests that Mazda considered this a major revision. The gears remain at B6S7-14-132 and B6S7-14-141, unchanged from '92.

For '95, the assembly undergoes only minor revisions (-100G and -100H), again reflecting changes to the plunger. (Boy, Mazda sure did a lot of work on that plunger.) Gears remain unchanged, still at B6S7-14-132 and B6S7-14-141.

'97 is completely unchanged.

In '99, everything changed. The assembly went through three major revisions, starting at BP4W-14-100 (through VIN-9301), moving through BP5A-14-100 (VIN 9301-0701), and ending at BP6D-14-100. None of these are similar to any NA, and I wouldn't expect them to be. Crank sensor, remember? (Distressingly, I can't find any part numbers for the actual cast housing.) The internal changes for the first rev change (at 9301) were fairly trivial. At the 0701 change, however, they changed the internal gears. Prior to that, they were the same as the NA. Afterwards, they went to inner = BP6D-14-132 and outer = BP6D-14-141. These pumps are all noted as applying to engines with a casting mark of "BP4W", which is definitely the '99-'00 engine.

The last catalog I have is for '01, and it's where things get weird. I downloaded this catalog directly from Mazdaspeed Motorsports' website (link) and it's marked "Mazda MX-5 Miata, USA & Canada ('01 > )"

That catalog lists exactly the same oil pump and internals as the '99 catalog. It also says that the casting mark should say "BP4W".

Trivia time for owners of VVT engines: Does the casting mark on your engine still say BP4W, or did they update it to read BP-Z3?

I know the back of my VVT block still says BP4W.

Casting mark on the head? BP4W

Clearances are factory spec. I have been running rotella 5w-40 synthetic.

If the relief valve is stuck, can I just whack the pan with a hammer to fix it?

You can whack the pan with a hammer as much as you want, but it will not fix the problem, if that even is your issue. I will take a picture of my old oil pump and where the relief valve is located for you tonight when I get home.

Don't listen to that noob. A hammer will fix it. If your oil pressure doesn't rise, that just means you're not using a big enough hammer/hitting hard enough. Try a 10lb sledge and wind up. Alternatively, you could sawzall the opening larger, which would be the best fix.

Stop spouting nonsense, I think he should start with a 15lb hammer and then move onto the sawzall.

I'm stuck.

On the one hand, I don't think there's any question that Travis' practical, hands-on experience with Mazda B-series oil pumps (and with Miata engines in general) probably outstrips mine by at least an order of magnitude. And as a rule, I find that people in that position are more often right than wrong if I find myself in the position of debating something like this with them. So I really, really want everyone (including Travis) to understand that I'm not calling him a liar here.

I just can't get over this contradiction with the Mazda catalogs. They say that the oil pump gears changed in '99, and then remained unchanged throughout at least '01. Rozenthal Mazda's website corroborates this, listing BP4W-14-100A as "Through 02/28/1999 production" and then giving BP6D-14-100 as "From 03/01/1999 production," and listing this part as valid all the way through 2005.

All I can really say is... I've had four Miatas, and found that Mazda likes to change things without any record. Frankensteining different years of Miata parts in my cars, I've run into this more than once. The dealer won't have any record of a change, but it can be obvious with the parts in your hand.

Are you guys trying to get me to fuck up my car?

I went to home depot and picked up some awls. I tried to hammer the awl into where I think the pump is on the block but it just bent :facepalm: So I guess the right thing to do is to go through the oil pan? But what point on the oilpan should I aim at and what angle should the awl face in order to hit the relief valve? /And once I get it in there, should I wiggle it clock wise or counter clockwise?

It could be very well that thats not actually when the gear change occurred. We need y8s back in here. Didn't you have the first mis-matched oil pump? **Pinging y8s

Don't listen to these guys! If its a stuck open relief valve (which is pretty unlikely actually) then the only remedy is a new housing.

Travis, remember that oil pump I sent you? I remember the gears were thicker and the housing was worn out well beyond the 30,000 miles on the motor. But I do not remember the measurements. Maybe they are in a thread somewhere...

I asked you before but I can't find the thread :( -- What's the max hot oil pressure you see, and what oil do you run?

So, Travis, to enhance my knowledge: Do you make these gears in two different thicknesses?

Yea i remember it, I just don't have the data. :X Was that a 99 housing? Although if I remember right the housing was like +.070 tapered. :bowrofl:

Actually 3: .37x .39x .43x

The increases in size are all in the width direction from factory and in the different assemblies I make. Apart from that the teeth/root dimensions are all the same on the different gears. The only root/tooth dimension changes are in the 89-91.5 years.

Interesting.

I just mic'ed the stock gears that came out of the oil pump on my '99 engine. Both gears came in at between .3722" and .3724". I remember measuring the new gears when I got them and finding that they were just a tiny bit thinner than the ones I took out, though the logbook with those measurements is buried away somewhere. I'd guess they were probably closer to the .37" spec you gave.

According to the VIN on the oil pan, and the potentially dubious list of all 10AEs, this car has a "born on" date of March 25, 1999. The complete VIN (from the oil pan) is JM1NB353XX0136036. Does that mean that this engine falls into the "After March 1, 1999" production class?

Dammit, I hate inconslusivity...

Crap. I need to measure my gears.

Got yourself a fancy sec of mics with 4 digit places :)

Yea, the ones we sell are a little looser on the width spec that fit into the stock housing. They are about .002 less then the stock gears. That puts their theoretical clearance at .0035-.0055 which is what we were aiming for.

That goes along with the scheme that the 99-00 gears are equal to the 91.5-97 gears. We need an 00 gear set and 01 gear set for final confirmation.