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Need Help With Engine Temp


Rearanger

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My gas mileage has dropped to it's worst level since I've tracked the truck from new. Four consecutive tanks yielded about 18 mpg when nothing else changed. I've had 18 mpg before but only for one tank then went back to 19, 20, 21's.

I started to investigate my engine temp. I purchased an "Ultra-Gauge", similar to "Scan-Gauge" in that I can pull out OBDII engine info on a screen.

I set it for engine coolant temp and got about 180 - 184F with a 195 stat. I didn't know if bad ECT or stat. Purchased a new ECT and installed, temp readings went to 172 - 174F. More accurate ECT?

I tested the old (original) ECT with accurate water heater, a resistance meter, and thermometer. The readings were out of spec (higher) even giving the +- 15% allowance from the manual. Lower ohms = leaner mixture.

Today I purchased a new (premium?) stat and installed. Test drive gave temp readings of 180 - 184F, an increase with the new ECT of 10 degrees.

FSM states stat should start to open 187.7 - 197.7F and fully open from 206.6 - 222.8F

Can anyone give some insight into if my temps are normal or low? Should I be seeing closer to 195F as a steady driving temp?

I'll keep track of mpg to see if, what seems to be extra 10 degrees, will give better mpg.

Thanks for any help.
 


RonD

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Yes, that temp is low

195degF on very cold days would be minimum.
Yes, it does lower MPG.

Check the fan clutch, make sure it is not stuck on "locked", spins at same speed as engine
Cold engine
Start engine
Run it for 1 minute then shut it off, this warms up the fluid in the clutch and allows it to be "released"
Pop hood and spin the fan, the colder the air temp the easier the fan should spin, but it should spin a few revolutions with a good pull.

Fan clutch is controlled by the radiator heat, not engine heat it has a spring on the front that is heated up by the radiator heat, as spring warms up fan starts to spin closer to engine RPMs.
If it is "always on" then engine is being cooled too much by air and rad coolant is too, so engine simply can't get hot enough.

Also feel upper rad hose, there should be no circulation to the rad until engine gets warmer, that is what the thermostat does, blocks flow to rad, rad is only for "extra heat".
So upper hose should remain cold for 4 to 8 minutes after startup or even longer if it is very cold outside, if it is warming up with the engine then something is wrong in thermostat housing, coolant is leaking past seal.
 
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Rearanger

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Ron, at this point I'm not ready to blame fan clutch. I tested the fan and when cold it does spin by hand when engine off. Now it's not in unrestricted free spin, but it is not locked.

I also think the stat should be able to override the fan. Certainly when you're going down the hwy at 60 mph you have no way to control the air flow or air temp - the stat should control engine temp. Older cars never had fan clutches and stayed in heat range of stat.

I'd like to know what engine temp determines proper hot fuel trim. When does the computer say the engine is hot enough for non-rich mixture. When engine is 189F is engine still running a little rich? How about 193F, still not hot enough?, Does it wait for the magic 195F?
 

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I have an older Scan Gauge. I usually see coolant temps in the 184º - 190º range. I'm getting ~18 MPG (and always have). Just out of curiosity, what RPM are you seeing when the engine is fully up-to-temp and the transmission is in gear (Drive)? My engine usually idles around 825-850 RPM when stopped at a traffic light.
 

Rearanger

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Bronco, my truck is manual trans, warm idle rpm is about 750.

Glad to see your temps about what mine are. All temp readings depend on the accuracy of ECT resistance. If the ECT is off in resistance values then temp readings will not be accurate. When I tested my original ECT the values were higher per temp than what FSM stated - meaning temps displayed would be lower, but not actual.

I don't think anyone yet understands how a thermostat is intended to operate and what normal operating temps are.

Still waiting for more input.
 

Bronco638

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RonD has a pretty good grasp on this stuff. I've read quite a few of his posts and he's usually on-target. I recently replaced my t-stat with a 185º unit. According to RonD, that's 5º too low, it should have been a 190º unit. So, I'm wondering if our engines are not operating in the proper water temperature range and we're noticing lower MPGs as a result.
 

Rearanger

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Bronco, my clutch fan is operating properly. That said the stat should maintain engine temp, given that air temps and air flow change, even without fan. Not sure how a clutch fan would stick locked anyway.

There is a crack open spec for stats, Ford lists mine as should be 187*, I'm wondering if that crack open position is enough to cool engine with winter air temps. The time coolant sits in the rad with lower temps means that its quench temp is lower, and that will cool engine faster when stat opens - even a crack.

In summer temps the stat may need to go to full flow open to maintain 195*, so engine temps may be higher.

New ECT sensor and stat did not improve running engine temp - so, is this normal? I'm going to test the new ECT to see how close to spec it is.
 

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I'd like to know what engine temp determines proper hot fuel trim. When does the computer say the engine is hot enough for non-rich mixture. When engine is 189F is engine still running a little rich? How about 193F, still not hot enough?, Does it wait for the magic 195F?
It's not that cut and dry. The computer had the ability to vary the injector pulsewidth in increments of a few thousandths of a second. It can vary the fuel mix infinitely within it's programmed spectrum to adjust for optimum warm-up and emissions across the entire temp range.


There is a crack open spec for stats, Ford lists mine as should be 187*, I'm wondering if that crack open position is enough to cool engine with winter air temps. The time coolant sits in the rad with lower temps means that its quench temp is lower, and that will cool engine faster when stat opens - even a crack.

In summer temps the stat may need to go to full flow open to maintain 195*, so engine temps may be higher.
This is probably contributing, but it should still be reaching the full operating temp. The t-stats on the 4.0 SOHC are a problem, and in the last five years I have done one during the summer, and at least one, usually more, each winter. Lower ambient temps make it harder to get to and maintain operating temp. If the weather has been extremely cold lately that may be your issue.

Try blocking off part of the rad with a cardboard box. If the temp comes up and MPG goes back up you may be on to something.

FWIW my truck has never done better than 18. At least not since they started putting corn in the gas. So it is also possible that the ethanol content in you area has gone up.
 
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Rearanger

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Thanks adsm08, I was hoping you'd contribute.

In NC we've had temps all over the place. Hard to nail down temp as the issue. I will block rad and see if engine temp increases.

Maybe just poor quality stats?? The one I took out was a Stant, "SuperStat", in less than a year. The new one is O'Reilly's "premium", as no local parts store on a Saturday had a 195*.

As I said, I'm going to check the new ECT temp/resistance values. The Ford one showed slightly higher resistance than spec'd, that would tell computer engine temp is lower than actual. Not a too easy job; pot of water, thermometer, multimeter.
 

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T-stat will open and close a few times on warm up, depends on engine load, i.e. how much heat it is generating.

As you said when t-stat first starts to open the warm coolant flows into rad from top hose then cold coolant in the rad is pushed into engine from bottom hose and cools the engine which closes t-stat until that coolant warms up enough to get it to start opening again, and that cycle continues until an equilibrium is created.
And that could be a partially or fully open t-stat depending on outside temp.

Yes, blocking the rad opening stops air flow in the engine bay lessening air cooling of the engine and heater hoses.
That's why they put those snap-on or zippered covers over rad openings on semi-trucks, engine simply can't generate enough heat to keep itself at operating temp with very cold air flowing over it.
 

Rearanger

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Ron, I can see when the stat opens from watching the heat gauge readings taken from the ECT. It sure doesn't open at all until reaching 185*. The stat keeps engine between 171.4 close to 185 open.

I shouldn't need to block the rad in NC, nor should I have to test a bunch of stats in order to get one that operates properly. My dash heat gauge (one wire) has stayed the same and does not indicate lower than normal temp, so most people would not notice a 10* difference in engine heat.

No one has posted who has an aftermarket heat gauge or scan gauge for me to compare with - maybe this is normal for winter operation.

As I said I need to test the ECT for accuracy, garbage in/garbage out.

I've been doing some research on fuel trims. Once in closed loop the computer adjusts to maintain stoichiometric so my loss in mpg might not be engine temp.
 

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Rearanger1 said:
Bronco, my clutch fan is operating properly. That said the stat should maintain engine temp, given that air temps and air flow change, even without fan. Not sure how a clutch fan would stick locked anyway.

There is a crack open spec for stats, Ford lists mine as should be 187*, I'm wondering if that crack open position is enough to cool engine with winter air temps. The time coolant sits in the rad with lower temps means that its quench temp is lower, and that will cool engine faster when stat opens - even a crack.

In summer temps the stat may need to go to full flow open to maintain 195*, so engine temps may be higher.

New ECT sensor and stat did not improve running engine temp - so, is this normal? I'm going to test the new ECT to see how close to spec it is.
You think you're getting that much cooling just from air circulation? I don't think I am and I'm in Chicago. We haven't seen 40º F outside temps for a few months. I wonder what would happen if you were able to remove your fan, as a test.

Based on my Scan Gauge, my cooling system maintains 184º to 190º F regardless of ambient temperatures. I went with a Motorcraft t-stat, when it was changed, last Fall. However, I'm willing to bet that Stant makes it for Ford.
RonD said:
That's why they put those snap-on or zippered covers over rad openings on semi-trucks, engine simply can't generate enough heat to keep itself at operating temp with very cold air flowing over it.
Well, that's not quite a fair comparison, diesel versus gasoline engine. Diesel engines are exothermic (they give off more heat than they produce, while idling). Gasoline engines are endothermic. The best way to warm up an engine, especially a diesel, is to put a load on it. I drove a Beetle TDi for the past 7 winters. The cooling system would normally lose ~10º of coolant temperature while sitting at a stoplight (in just a couple of minutes). I doubt the radiator fans ever kicked on, all winter long. I even partially blocked off the radiator, one winter. That had no effect, VW had that cooling system working as well as it could.
 

Rearanger

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Partially blocked the rad today, no change in stat operation as it looks to be operating like 185F even though it's stamped 195F. Going to test ECT sensor this weekend.
 

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I have had several thermostats not function in the advertised range, its frustrating, you may need to pull it and replace it again, I have a 190 stat, mine runs in the 183-187 range on the scangauge II, almost all the time. I like Napa brand stats, just had better luck with them and you can get them in 5 degree increments for most applications, once you know what size your stat is.

JP02XLT
 

JP02XLT

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I have had several thermostats not function in the advertised range, its frustrating, you may need to pull it and replace it again, I have a 190 stat, mine runs in the 183-187 range on the scangauge II, almost all the time. I like Napa brand stats, just had better luck with them and you can get them in 5 degree increments for most applications, once you know what size your stat is.

JP02XLT
 

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