slogfilet

iTrader: (1)

I have a 1994 VX with the original D15Z1. When I bought it 6 years ago, I installed a 195 degree thermostat, due to internet wisdom of "hotter thermostat = moar mpgs."

The D15Z1 calls for part number 19301-PZA-305, while others of the generation call for 19301-PAA-306.

1. What are the temperature ratings for each of those part numbers? I'm getting conflicting information (170, 180, 193/195), and I don't have my Helm of Wisdom handy (see what I did there?)

2. Is there credibility to the theory that a hotter thermostat would yield better fuel economy? From what I understand, it would open the 'stat later, not affecting the final operating temperature of the engine. There must be *some* difference, hence the two different part numbers.

It is of note that my current thermostat is a cheapy from Autozone, I have no evidence of increased or decreased fuel economy, and I would rather default to the correct (OEM) configuration unless there is compelling evidence to the contrary.

Former User

Always start with the service manual. How can you not keep the manual handy?

slogfilet

iTrader: (1)

Thank you!

Based on those numbers, what are the "nominal" values for the thermostats? Looks like 180 for the D15Z1, else 172.

So... currently my current thermostat is 15 degrees "too hot" over the OEM spec. What effect does the thermostat rating have on the engine (and specifically with fuel economy)? Honda saw fit to spec a 10 degree difference for the Z1, but more is not necessarily better.

(My manual is not handy due to being at work. I'm at work, not my manual.)

EDIT: Yes, this is basically a question of "What does a thermostat do, dur?" but with the characteristics of the VTEC-E, I'd rather ask here than find incorrect information elsewhere.

Former User

I read the numbers as saying that the high fuel efficiency of the D15Z1 depends in part on it running at higher average temperatures than the basic Civic engines.

Why question the Honda engineers? They have my respect. Buy a Honda thermostat and call it a day.

And take your Helms to work with you. Doesn't everybody?

slogfilet

iTrader: (1)

Good point. I don't necessarily see it as questioning the engineers... even with the increased fuel economy of the VX, they had to cater to a relatively large market, and there could be ways to eke out more economy (if at the cost of "performance"). We modify our cars quite often, sometimes quite contrary to the Honda engineers' decisions; whether it be for increased HP or increased MPGs, there are certainly ways to improve, if you keep in mind the trade-offs. I don't mind tailoring my driving to the needs of lean burn, perhaps moreso than the typical Honda enthusiast.

Tell you what... I'll finally get my mpguino hooked up, run it with the 195 degree 'stat that's in there, then change it over to OEM and report back. It might not be ABA testing, but one anecdote is arguably better than my speculation.

And as of about 15 minutes ago, a pdf of the manual has magically appeared in my work email box. Weird. No excuses!

StewieVX

@slogfilet so you ended up running 180F thermostat? Did your mpgs improve over 195F?

I'm confused with service manual verbiage. First it states d15z1 (176-183)=180F thermostat, then it says EXCEPT and lists d15z1 again and it states (169-176)=170F. So which is it essentially 180 or 170 ? LOL

I have googled another thread and in this thread guy states it's actually suppose to be 170F for VX and most parts stores incorrectly supply 180F thermostat. I would obviously default to VX service manual but again the verbiage with EXCEPT is confusing to me!

Service manual actually references both 170 and 180F thermostats referenceing same D15z1 engine. Now i'm totally confused.

Thoughts guys, anyone? I will be placing an order soon for thermostat so i would like to get this sorted out please. Thank you kindly.

https://civic-eg.com/forum/viewtopic...357727#p357727

StewieVX

Update

It's 180F correct thermostat for VX D15z1 engine.

I was digging in 1992 honda civica SERVICE MANUAL and this is what i found.

P.S
There is another hotter thermostat with 192F opening but may not be advisable to use it. General theory is hotter thermostat yield better fuel economy but may be at cost of more engine wear. I think Honda designers knew best.

TomCat39

Just to clarify. First line is D15Z1 and it's temp which is a the 180F. Second line is Except the D15Z1 (So is for D15B7, B8 and D16Z6) is the 170F. Then 3rd line it shows the D15Z1 specific full opening at 95C and then 4th line is Except the D15Z1 (Once again the D15B7, B8 and D16Z6 motors) is 90C.

The except is ALL except such and such motor aka All but the D15Z1.

NukeNinja

I used a 192 F thermostat in my VX with no issues. Honda engineers may know best, but they definitely have different goals and objectives in mind when making design decisions, e.g., emissions. I also did not see any measurable change in fuel economy at the higher coolant temps.