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180-thermostat = richer mixture?

I am preparing to retest Charlene, who posted high HC marks on the last go-around. (see website for test results.) I've contacted the owners of the shop who put my exhaust system together, and they assured me again that their high-flow cats were the best made, and should easily scrub HC's as well as OEM's.

They ran down other possible causes, and one clearly stuck out: a low-temp thermostat. (He indicated that worn O2 sensors may have contributed, but probably weren't the culprit unless the MIL was lit.) I told the tech that the engine had a 180 installed, and he indicated that this may be the problem, even if the engine is running in closed-loop mode and no MIL is set. I've always heard that engines do indeed run slightly richer when cooler, making a bit more power.

Cosmic truth or bullshit?

I installed this little gem early on to prolong the life of underhood parts. Is it possible that I've shot myself in the foot with this homebrew el-cheapo mod? Would switching from the OEM 205 to a 180 degree thermostat indeed raise tailpipe HC content enough to test high, without setting the MIL?

If this is indeed the case, I will cease suggesting that others install 180's, power-increase or not. (For the record, I did NOT notice any power increase after installing the 180, but left it installed figuring it wouldn't affect anything but underhood temps.)

Any educated comment appreciated. Please, no flamebait. I'm sure Ford spec'd a 205-degree thermostat for a reason. Could it be to lower tailpipe emissions? Improve driveability? Faster warm-ups which lower overall tailpipe emissions? To warm my Birkenstocks' faster on frosty mornings?

-JD

_________________________________ JD's Locally-Famous Mustang Page: http://207.13.104.8/users/jdadams

Reply to
JD Adams
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Sort of. It depends on the ECU program. Generally speaking, if the ECU is running closed-loop, I tend to doubt that you'd see higher HCs with a

180F thermostat. While I'm not an expert on ECUs in general and specifically not on the current Ford ECUs, the coolant temperature primarily influences the cold-start enrichment program. During cold-start enrichment, the engine usually runs open-loop (it's likely that the O2 sensor is too cold to work correctly anyway). If a 180F thermostat is low enough to prevent your ECU from exiting the cold-start enrichment program, I suppose it could increase HCs. However, I'd rather expect an MIL in this case, though I haven't looked at the OBD II codes to see if there's an appropriate code define.

I suppose it's possible that coolant temp has some influence under normal operating conditions, but this strikes me as unlikely. The question is, does your ECU treat 180F as 'normal' when the stock thermostat is set to 205F ? I guess you could try swapping the stock thermostat back in, but I much more suspect that aftermarket exhaust system and high-flow cats are the culprits. Does the aftermarket system dramatically relocate the O2 sensor?

Dana

Reply to
Dana Myers

My understanding is that, yes, the EEC does treat temperatures encountered with the 180°F thermostat as normal. The 160°F would cause problems.

Reply to
Keith

That's my understanding as well.

Dana

Reply to
Dana Myers

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Reply to
Rein

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Reply to
Rein

Actually, at least on my 88GT the stock thermostat should be 192. I also had a colder thermostat in mine for awhile. I didn't notice any improvement, went back the 192 years later, and the car appeared to start runing a lot better. Could be an age thing.

Reply to
Ironrod

Reply to
Michael Johnson, PE

I am in agreement. I conferred with the testing station this afternoon in anticipation of a test check next week, and was told that unless the MIL was on, a 180 probably didn't make THAT big a difference. He did indicate that most newer cars operate more efficiently at 195+ degrees, and that slighly higher emissions would result from using a 180 in an engine spec'd for

195-205.

Alas, he concurs with the group: the high flow cats aren't getting the job done will enough; he suggests retesting with new O2 sensors/stock thermostat (195? 205? An OEM unit will go in, and I'll know for sure then), and if it is still above 20 grams in both 15/25 mph testing, have 2 more pre-catalysts installed.

For that kind of money, I may just swap the OEM catalytic H-pipe back in. Maybe Tim can help me out on that one.

-JD

_________________________________ JD's Locally-Famous Mustang Page: http://207.13.104.8/users/jdadams

Reply to
JD Adams

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