let the car sit overnight, remove the EGI fuse and crank the engine for 2 seconds, pull the spark plugs and look for coolant on them. a cold engine rough idle and overheating issue combined usually point to bad coolant seals. yes, i am the bearer of bad news that no one seems to like.

if the plugs are wet and it won't burn off with a lighter within a few seconds and they smell sweet, its an indicator of coolant and a needed engine rebuild.

spending 20-30 minutes on this test versus hours on diagnosing a phantom cooling system issue is a better 1st step.


the massive jump in temps when driving is caused by a massive air pocket in the cooling system, when coolant finally does flow enough to touch the temp sensor it begins to read the actual temps instead of air. coolant temp sensors do not read air pockets accurately.

if you want to verify this you can also do a hydrocarbon in cooling system test with a combustion leak detector, which are available at harbor freight. there is also the bubble test with funnel for a third definitive visual of air getting into the system from a potential coolant seal failure.

 

Coolant smell in the exhaust as well?

 

Starting with the easy route, thermostat and then go From there. It’s the original to my knowledge so it needs to be done anyways. Ray is great, but after shipping it was almost $40. Which of these have a good reputation as a replacement? I’ve only heard of the STANT. Much less expensive from Rock.

 

Most aftermarket thermostats don't have the block-off for the warmup bypass passage and can cause over heating.

 

Buy a new OEM T-stat from Japan, N3A1-15-171. https://www.ebay.com/itm/264698496266
If you don't get a "set" you'll need both numbers for the stat and gasket. N3A1-15-171 THERMOS, N3C1-15-173 GASKET

The USDM thermostats are rebranded aftermarket parts. https://www.rx7club.com/3rd-generati...ilure-1161193/

 

The order flips in my pics below, JDM OEM is on the right in the first pic and then on the left in subsequent pics

 

So, best bet is going thru Ray and getting it from Mazda then, hence the price difference I’m guessing.
His part # is 8AF6-15-171-9U, different than the one in the picture? Would I still need the second part as well?

 

I suggest exercising more diligence than trusting AI. The usdm 9U t-stat is a motorad that is lower quality.

 

I googled it, I asked what is the difference between the two and it gave me that. Then I asked Ray and he says it’s the full Thermostat with gasket. Not sure what further diligence I can do aside from physically comparing the two, or ask the board, which is what I’m doing. Even Motorad’s site says it’s a Mazda part, “interchangeable with Mazda 8AF6151719U.”
Everything suggests it’s as good and OEM except your last comment.

 

It’s not OEM though. It’s a motorad stuffed in an OEM box with a Mazda USA label. The machining and fit and finish on the Mazda Japan stat is much better as evidenced by the pics above.

Sure the aftermarket one will work, but after I had one fail early I’ve never gone back.

 

Not arguing with you, just curious where you find it’s a Motorad produced product? I’ve searched and everything says it’s OEM, even Mazda itself. I searched “is “part #” produced by Motorad” and it said no, it’s an OEM part #.

 

I forget exactly which OEM thermostat I bought, but it's probably the US one and it has been working for years. But if you can spend $20 extra for a better part that sounds like a good plan. Cooling system upgrades are generally a good idea on a turbo rotary. My vote is to check the spark plugs as suggested earlier ( https://www.rx7club.com/3rd-generati.../#post12639436 ), and buy the Lisle funnel so you can get air out of the system when installing the new thermostat. And be sure to check the new thermostat in a pot of boiling water to verify it opens as expected. If you're sure the coolant seals are OK (because the system holds pressure and doesn't get water on the spark plugs after sitting with the engine off), I might also flush the coolant using Thermocure and distilled water.

 

For reference:

(It is not 100% certain that it is the correct OEM part, but the box looks correct. It is common that the part number is blurred out on these auction site items.)

Seller seems legit. If you click on his name you can see his other items. You can then search for his RX-7 items. Seems he has access to a good list of NOS/NIB FD parts.

https://buyee.jp/item/jdirectitems/a...n_DirectSearch

 

I'm about to buy one of these just because my washer fluid reservoir just cracked and this is probably next. But since there are two versions of this tank (pre/post 99 spec front-end) do you know how it works if you've done a 99 spec front-end conversion? Apparently the old one has fitment issues with the 1999+ front crash bar but I haven't confirmed much yet.

Anyway, enough off-topic stuff, but @OP I had a similar issue when I bought my car because it has a shitty FMIC install and overheated when parked after driving around in summer traffic. Using water wetter and doing a coolant flush to get any air out helped a bit (took the mechanic a couple tries).

Also, does the idle smooth out when you turn your AC off?

 

It's stamped onto the side of it.


OK.

It's a part accepted as OEM equivalent and distributed by Mazda USA.

If it's what you want, buy it.

 

Hot water test, didn’t move. I think I found the issue.

 

I bought one last night for C$180 (before all the pother costs). I have a '99 bumper. I was not mindful of any issues between '93 & '99. The last one i bought fit in without issue. I am buying this one for a friend with a Spirit R experiencing similar overeheating issues. Maybe we will grab that Thermostat and also a new AST.

Prices were over C$230 for the resevoir last week, but suddenly dropped to C$180.

 

https://buyee.jp/item/jdirectitems/auction/x1194677378

 

Have him pop out the thermostat and test it, 3 bolts and 5 minutes to get it out. It answered my question as to why I overheated.

 

ok yeah, that's the pre1999 / series 5&6 version. I guess if the current one fits then the older version should as well, will give it a shot.

 

N3G1-15-350A matches the parts catalogue for the 265hp engine for 1999.

Interestingly for 255hp (AT) and 280hp motors for 1999 the part number is n3A1-15-350B.

The part number for Version 3 cars (1995) is N3A1-15-350B (as well).

I wonder what the difference is.?Curious the1999 280hp motor cars have the earlier version.