Broken thermostat = greater fuel consumption!!

[RedeemedSoul]

Okay heres the debate:
My friend has a 94 N/A camry. His car recently stopped working and he ventured to seek reasons why. He discovered upon inspection his thermostat spring was shot and the thermostat was not accurately reading engine temperatures also his radiator fan turned off. He had to refill coolant/anti-freeze like once a week from this problem up until his car stopped working. He now has fixed the problem and his car is running again as well as the radiator fans.
He claims:
Now that his thermostat can accurately read engine temperatures again that it isnt burning as much fuel anymore and in result he went from 11mpg to 26mpg...
My rebutal:
How would a thermostat with innacurate engine temps amount to greater consumption of fuels.
1- It does not change Air/Fuel Ratios
2- Does not directly affect Fuel Injectors
3- Does not directly affect Fuel Pump

I would give him the benefit of the doubt that the engine heat level increases would show that oil can have been excessivly burned but we cannot determine that.

Thank You for all mature responses!
Please post if you have specific knowledge or just want to throw in your experiences/$0.02 cents...

My friend does post and frequent these forums daily, but i will save him the trouble of posting his name for now.. if he is correct i will give him the glory he desires!!


- Soul

[DarkMastyr]

If the thermostat is reporting temperatures that are very low, your ECU may never switch to closed loop operation. It may be stuck in open loop "warm up" operation in which your A/F is very low (rich) to compensate for the condensation of the fuel spray on cold surfaces.

[JetspeedCamry]

Thermostats don't report or read tempratures........

[DarkMastyr]

Sorry I was thinking about the engine coolant temperature sensor. Never mind then.

[BakaWill]

hmmmm...... if his thermostat stuck closed (like the little F****** like to) then the engine will over heat and your heads will probably warp then youll be screwed. but if it survives without warpage then it would just be boiling off coolent.

if it stuck open then the coolent in the engine would be bypassing it and taking longer to heat up. then the ecu would using the temp sensor like dark said run in "warm up mode".

if it was not his thermostat at all but his temp sensor had gone bad and his car was overheating. (probably the only way he would loose radatior fluid without a leak.) he needs to check his oil probably draning it would be the best way and make sure that it isnt kinda light and frothy. cus then hes got a blown head gasket and hes gotta replace.

[RedeemedSoul]

Isn't it that it is in "closed loop" during warm up and then "open loop" after warm up? I thought that was once warmed up, it used open loop for fueling because it was using the o2 sensor etc...


taken from a subaru forum... thanks for all responses keep them coming!

[Grayguy]

Iknow upon replacing my bad thermostat I went from 21mpg back up to 29mpg

[BakaWill]

the ecu has no way of knowing wheather the thermostat is open(hot) or closed(cold). if it was stuck open the coolent flowing past it would cause the engine to run colder and the engine would run in warm up mode kinda misleading as more fuel(rich mixture) makes the engine run colder. it keeps the fuel from condensing on the cold surfaceses and its more gentle on the parts as they thermally expand so they can expand uniformly and not fracture under the associated stresses.

[DarkMastyr]

Originally Posted by RedeemedSoul

Isn't it that it is in "closed loop" during warm up and then "open loop" after warm up? I thought that was once warmed up, it used open loop for fueling because it was using the o2 sensor etc...


taken from a subaru forum... thanks for all responses keep them coming!

I think it's the other way around. Open loop = no feedback control, operating off a range of preset values. In cold startup conditions, your ECU will just keep dumping massive amounts of fuel to ensure that you have enough in vapor form for combustion since a large amount tends to condense on cold surfaces. The equivalence ratio (F/A vs. F/A stoich) can be known to approach 10 for some cars operating under this condition (meaning you're dumping as much as 10x the fuel required under normal operating conditions). Closed loop = implementation of a feedback loop that takes into account measurements such as your narrowband O2 sensor to adjust the fuel accordingly so that you run at a proper A/F ratio with proper emissions, etc.

[a94autoCamry]

Originally Posted by Grayguy

Iknow upon replacing my bad thermostat I went from 21mpg back up to 29mpg

can you enlighten me on how did u know ur thermostat went bad?? i think i have a problem with my thermostat i think??

when i drive on the streets, the engine temp gauge shows about halfway which is normal but then once i hit the freeway, the gauge goes almost all the way down and sometimes even touching the bottom line.....so is this a bad sign the thermostat is bad?? cuz like you i'm also getting 20-22 mpg on the 5sfe....

seems like my thermostat is stuck on "open position"

[pcgeek]

If the thermostat was defective... it would more than likely be in one of two states stuck open or closed...

1. Stuck closed the coolant wouldn't circulate and in turn it would over heat the engine ....

2. Stuck open the engine would NEVER reach full operating temperature as seen by the sensor and sent to the ECU. Which would cause it to run rich all the time. There fore it would have crappy MPG.

pcgeek

[NowUCMeNowUDont]

the thermostat has a spring where it can open and close ... when i had a coolant problem where my cars temp when sky high and the coolant was boiling in the resevoir...i checked my thermostat...the only way you can is opening the thermostat housing located on the engine end of the bottom radiator hose....its the metal tubing right before the water pump... ull need 10 mm combination wrench(one side has the circle wrench and the other normal wrench))...for one of the nuts..theres two of them...when i got my old thermo out the spring was stuck compressed so the thermo was basically stuck open...its embarrassing but i was actually doing a V8 kinda 12 mpg...i just replaced it with one from the car parts store for 6 bux and rememebr ot replace the gasket 1 buck....and now my mpg is back to 26

[chronoti]

Originally Posted by a94autoCamry

can you enlighten me on how did u know ur thermostat went bad?? i think i have a problem with my thermostat i think??

when i drive on the streets, the engine temp gauge shows about halfway which is normal but then once i hit the freeway, the gauge goes almost all the way down and sometimes even touching the bottom line.....so is this a bad sign the thermostat is bad?? cuz like you i'm also getting 20-22 mpg on the 5sfe....

seems like my thermostat is stuck on "open position"

yes your thermostat is bad

[MrSo0h0o]

Originally Posted by chronoti

yes your thermostat is bad

so you are saying if at regular street driving the temp is at half, but then if you do highway driving and it goes down the thermostat is bad?? i always figured it went down b/c you are going at a higher speed and the cool air coming into the engine bay cools the engine down better? if so, maybe thats the reason why my mpg is so bad?! and on a normal operating car, how does the temp gauge respond?

[RningOnFumes]

I agree with Chronoti.

I replaced my thermostat not too long ago. My temperature stays constant at about right under the halfway mark and stays there once the car is warmed up.


Someone back me up on this part:

The engine needs to stay at a particular temperature to be optimum in operation. It can't be too cold nor can it be too hot, thus the need for a thermostat to regulate the temperature.

If the car gets cooler as it speeds up....that would mean you have a faulty thermostat that is stuck open.