Sometimes it runs rich, and sometimes we get awesome MPG's

[Voymom]

I have been increasingly agitated with this truck. There are times when it seems to get amazing gas mileage and other times it seems to be so bad we have to budget extra gas money into our monthly expenses. Our temperature also seems to be slightly on the fritz, mind you we just replaced the t-stat about 2 months ago because it was running extremely cool. Now it seems to run right at 210 and sometimes it runs 180/190. It has also been decreasing or cooling off (on the gauge) when we get on the gas, it does eventually get back up to temp, it's just really bothersome as we just changed the t-stat. I plan on putting in a new sensor, and new fuel filter to see if that helps with not only this issue but the rough idle/stalling problem.

These issues seem to only happen every once in a while, and does not do it all the time. Air temp doesn't seem to play a part either.

What other options should I consider in fixing these issues? All fluids have been drained, flushed and refilled as well. Could we possibly be looking at a new t-stat again? And what would cause the t-stat to constantly go bad? I have a feeling there is a bigger underlying issue with this thing, but I have no idea where exactly to start.

Thanks!

 

[Bartonmd]

Sounds to me like a water pump could be the cause... It doesn't flow much at low RPM, so the thermostat opens way up, then the RPM goes up, and it flows a lot of water, but the thermostat is the last one to know (on the way out of the engine, when the gauge sensor is on the side of the block, IIRC), so it always has to play catch up... This will cause your engine to be rich any time the water temp is cold.

Mike

 

[Voymom]

Sounds to me like a water pump could be the cause... It doesn't flow much at low RPM, so the thermostat opens way up, then the RPM goes up, and it flows a lot of water, but the thermostat is the last one to know (on the way out of the engine, when the gauge sensor is on the side of the block, IIRC), so it always has to play catch up... This will cause your engine to be rich any time the water temp is cold.

Mike

Thanks Mike!

Now if my water pump was bad would I get the SES light? My truck seems to be on the slow side when it comes to throwing codes. I never got a code for my t-stat, or my Power steering pump. I did get the SES for the CPAS, but that's about it.

 

[AtlWrk]

The only feedback the PCM gets from the cooling system is from the coolant temp sensor and the fan clutch (unrelated to your issue). As you saw with the thermostat things have to get pretty bad before it will actually set a code. It could be the pump or a lazy thermostat (even a new one may be slow to close). My temps get down into the 180s if I really get on it (on-ramps). Like Bartonmd said, the thermostat is the last to know when coolant temps in the engine have dropped.

Sidenote: the power steering system has no electronics whatsoever. It's 100% self-regulating and independent of the PCM so you never would see a code from that.

 

[Voymom]

The only feedback the PCM gets from the cooling system is from the coolant temp sensor and the fan clutch (unrelated to your issue). As you saw with the thermostat things have to get pretty bad before it will actually set a code. It could be the pump or a lazy thermostat (even a new one may be slow to close). My temps get down into the 180s if I really get on it (on-ramps). Like Bartonmd said, the thermostat is the last to know when coolant temps in the engine have dropped.

Sidenote: the power steering system has no electronics whatsoever. It's 100% self-regulating and independent of the PCM so you never would see a code from that.

Makes sense, however my t-stat was pretty bad. I do have a ticking noise which was present when I bought it, dealership I am good with diagnosed it as a faulty or failing fan clutch, but it hasn't gone out just yet so I'm leaving it be for now. One good thing about being a mom is being able to tune things out lol. Is there any definite way to check to see if the water pump is failing?

And since I don't have an SES light on, should I assume that the temp sensor is not the cause of my issue?

 

[navigator]

if I recall replacing the fan is kind of a pain so you might as well replace the water pump since you have it out.
Also, if you didn't replace the temperature sender when you replaced the Tstat many recommend doing that at the same time.

I have the Tstat, sender, hoses and new coolant waiting to go in when I get time.

 

[AtlWrk]

The ticking fan clutch is a well-known issue for pre-2005 vehicles. It's just the way the PCMs were programmed and isn't really an issue from a functional standpoint. You can get your PCM flashed with a 2005+ calibration to clear that up but most dealers charge ~$100 for this 5 minute job.

How are you checking your temps?

 

[Voymom]

The ticking fan clutch is a well-known issue for pre-2005 vehicles. It's just the way the PCMs were programmed and isn't really an issue from a functional standpoint. You can get your PCM flashed with a 2005+ calibration to clear that up but most dealers charge ~$100 for this 5 minute job.

How are you checking your temps?

Had a local dealership run the tech 2 on it.

 

[MacMan]

..... diagnosed it as a faulty or failing fan clutch, but it hasn't gone out just yet so I'm leaving it be for now......

WHY???? That very well may be the cause of the fluctuating temps....intermittent fan clutch operation.

IMO, be pro-active on replacing things that are "iffy"......get the fan clutch, water pump, and temp. sensor changed, all at the same time....if it fails while you're far from home, just imagine what a strange dealership/repair shop is going to wack you, $$-wise, since you're at their mercy.

 

[Voymom]

WHY???? That very well may be the cause of the fluctuating temps....intermittent fan clutch operation.

IMO, be pro-active on replacing things that are "iffy"......get the fan clutch, water pump, and temp. sensor changed, all at the same time....if it fails while you're far from home, just imagine what a strange dealership/repair shop is going to wack you, $$-wise, since you're at their mercy.

If it's the fan clutch causing the fluctuating temp, why hasn't it done it from the beginning? I have had the truck for almost 4 months, and the ticking was there when I went to look at it on the car lot. It has never given us an issue before, it never fluctuated. We noticed this issue about 2 weeks ago.

If something goes out while we are away from home it won't be to much of a big deal. I have roadside assistance and towing coverage insurance. I would have it towed to my driveway and my husband and I would do all the repairs ourselves. If we can't I have a wonderful relationship with a lot of mechanics around here. Plus I live in a very very very small town, if I'm driving anywhere away from home, it's no more than 3 miles away from my driveway.

I go by the rule of thumb, that if it's not broken, don't fix it. My fan clutch is on it's way out, so it has some life to it, however long it may be. But until it completely takes a crap on me, it's going to keep on ticking right along. I honestly don't see the fan clutch being the issue though, because like I said before, the temp fluctuations just started 2 weeks ago, and the fan clutch has been going bad since I bought it, and probably well before the PO traded it in.

But, I will keep it in mind

 

[CaptainXL]

What's your city mileage? You have an XL. Its gonna be around 12 or 13 since its been hovering around 35degrees the past few weeks. Short trips make for even worse mileage. As you stated you are no more than a few miles from home.

Do this. Fill up the tank. Get her on the highway and drive 20 miles. Then fill it back up. Divide the miles driven by how many gallons it took to fill up.

 

[Voymom]

What's your city mileage? You have an XL. Its gonna be around 12 or 13 since its been hovering around 35degrees the past few weeks. Short trips make for even worse mileage. As you stated you are no more than a few miles from home.

Do this. Fill up the tank. Get her on the highway and drive 20 miles. Then fill it back up. Divide the miles driven by how many gallons it took to fill up.

Yes I have an XL. My city driving is 12.5 exact but that's with me driving It hasn't been 35 degrees here at all. We had a few nights where it got a bit chilly, but no frost.

That makes a little more sense, I know the stop and go traffic doesn't help with the gas mileage, maybe my MPG's are normal? But that doesn't explain the fluctuating temps.

We are getting roughly 25 hwy and 12.5 city.

 

[CaptainXL]

Yes I have an XL. My city driving is 12.5 exact but that's with me driving It hasn't been 35 degrees here at all. We had a few nights where it got a bit chilly, but no frost.

That makes a little more sense, I know the stop and go traffic doesn't help with the gas mileage, maybe my MPG's are normal? But that doesn't explain the fluctuating temps.

We are getting roughly 25 hwy and 12.5 city.

Eh? XL's only get around 19 MPG on the highway.

The temp gauge on the dash is a fabricated indication of what the real temp is. In my case I have a new tstat and temp sensor yet when I use Torque my temps can be anywhere from 175 to 195 and still hover around the 210 mark on the dash gauge. You need to get a scan tool and measure the exact temp the pcm is seeing from the cts. Your just playing a guessing game going by the dash gauge. Let this be a lesson to everyone on how a proper diagnosis of the cts is made.

 

[Voymom]

Eh? XL's only get around 19 MPG on the highway.

Yeah that's why I said roughly 25 hwy. And we drove from here Mount Pleasant Iowa to Creston Iowa which is a 2 hour and 42 minute drive(open roads with lots of hills) it's 157 miles from my front door, one way. And we filled up before we left(gas station is a mile from my door) and when we got home from creston, truck was only on a half tank.

So 25.12 miles to the gallon. We drove over 314 miles and only used a half tank of gas.

 

[CaptainXL]

Yeah that's why I said roughly 25 hwy. And we drove from here Mount Pleasant Iowa to Creston Iowa which is a 2 hour and 42 minute drive(open roads with lots of hills) it's 157 miles from my front door, one way. And we filled up before we left(gas station is a mile from my door) and when we got home from creston, truck was only on a half tank.

So 25.12 miles to the gallon. We drove over 314 miles and only used a half tank of gas.

Lol. The halfway point on the gas gauge is not literally half. The gm engineers got you again. Roadie can you please elaborate sir?

 

[Voymom]

Lol. The halfway point on the gas gauge is not literally half. The gm engineers got you again. Roadie can you please elaborate sir?

That's what I figured. Nothing on these trucks(gauge) wise is exact. But we did drive it that entire week(our creston trip was on a Sat) and we didn't need to fill it up until the following Sunday, and that was with a 60 mile trip both ways on a Tuesday. Then I drive about 6 miles a day(Both ways) to drop kids off at school and pick them up Mon-Fri, Hubby drives 8 miles both ways to work Mon-Weds, and probably 3 trips to wal-mart (8 miles both ways) a week. All on that single tank of gas.

I will have to try what you said to figure out the gas mileage. Now that it appears that the truck is using gas normally for it's driving conditions, I'm still concerned with why it would be fluctuation temps? Is there any way to "test" the water pump?

 

[CaptainXL]

That's what I figured. Nothing on these trucks(gauge) wise is exact. But we did drive it that entire week(our creston trip was on a Sat) and we didn't need to fill it up until the following Sunday, and that was with a 60 mile trip both ways on a Tuesday. Then I drive about 6 miles a day(Both ways) to drop kids off at school and pick them up Mon-Fri, Hubby drives 8 miles both ways to work Mon-Weds, and probably 3 trips to wal-mart (8 miles both ways) a week. All on that single tank of gas.

I will have to try what you said to figure out the gas mileage. Now that it appears that the truck is using gas normally for it's driving conditions, I'm still concerned with why it would be fluctuation temps? Is there any way to "test" the water pump?

I think you are Ok with everything. Your highway mileage (when you are done calculating it) will tell the tale. A bad water pump either has bad bearings and is noisy or the impeller is shot. Remove the belt and spin the pump by hand. Notice any up and down or in and out movement? Other than that it could seize but not from experience on this model.

 

[Voymom]

I think you are Ok with everything. Your highway mileage (when you are done calculating it) will tell the tale. A bad water pump either has bad bearings and is noisy or the impeller is shot. Remove the belt and spin the pump by hand. Notice any up and down or in and out movement? Other than that it could seize but not from experience on this model.

Okay, THANK YOU! I haven't had to deal with a water pump in any vehicle so this will be my first lol This truck sure has taught us a lot in mechanics in the last 3 months. If I didn't love it so much I'd be tempted to call it a POS

I think the mileage is okay too, I just didn't realize how much of a BIG difference city driving was to hwy in these things. I had a Buick Rendezvous that got pretty decent mileage both ways, but that thing was by far the crappiest car I have ever owned in my entire life.

I will check the water pump, and maybe switch it out anyways. We plan on doing the idler pulley, and temp sensor too so might as well. Could the stepper motor just be going bad? And nothing be wrong with the temp/t-stat at all?

 

[CaptainXL]

Okay, THANK YOU! I haven't had to deal with a water pump in any vehicle so this will be my first lol This truck sure has taught us a lot in mechanics in the last 3 months. If I didn't love it so much I'd be tempted to call it a POS

I think the mileage is okay too, I just didn't realize how much of a BIG difference city driving was to hwy in these things. I had a Buick Rendezvous that got pretty decent mileage both ways, but that thing was by far the crappiest car I have ever owned in my entire life.

I will check the water pump, and maybe switch it out anyways. We plan on doing the idler pulley, and temp sensor too so might as well. Could the stepper motor just be going bad? And nothing be wrong with the temp/t-stat at all?

Your guessing again. Don't go by the dash gauge. Even if the dash gauge was bad it would take less know how to change the cts. Even then you absolutely need a scan tool to accurately diagnose the cts.

 

[Voymom]

Your guessing again. Don't go by the dash gauge. Even if the dash gauge was bad it would take less know how to change the cts. Even then you absolutely need a scan tool to accurately diagnose the cts.

That's the issue lol I have always relied on my gauges, and it's a hard habit to break. I need to find a scan tool for a decent price so I can do it myself. It's quite expensive to have it diagnosed. And maybe I'm just over reacting, us women have a habit of doing that

Should I just leave well enough alone until something dramatic happens? I know when my t-stat was bad it wasn't until I came here that I found out. I thought it was fine at 165* driving down the road with a lead foot.

The inaccuracy of the gauges on the buick was part of the reason why I hated it. My fuel gauge would go from empty to full no matter how much gas we had in it, and the temp gauge would bounce around like you wouldn't believe and it ran slightly warm. After coming here, I believe the stepper motor was bad in it, but even if it was I wouldn't have fixed it because I hated that truck.

I'm still learning the mechanical side of things with being a vehicle owner, so diagnosing possible issues is still new to me. I wanted to buy a tech 2 scanner, but the 1k(Ebay) price range is a bit steep for me lol

 

[HARDTRAILZ]

Replace the fan clutch and do the waterpump while you are at it. Had similar issue and that is the fix

Invest in a scanguage as well. You can see real temps and read and remove codes. Money well spent.

 

[CaptainXL]

That's the issue lol I have always relied on my gauges, and it's a hard habit to break. I need to find a scan tool for a decent price so I can do it myself. It's quite expensive to have it diagnosed. And maybe I'm just over reacting, us women have a habit of doing that :biggrin

If your CTS (Coolant Temp Sensor) is not working right then you would get a CEL (check engine light). There are certain tests that the PCM performs to check that the CTS is working within specified norms.

Should I just leave well enough alone until something dramatic happens?

Nothing dramatic will happen but if you don't have a scan tool then all you have to go by is the Check Engine Light from the computer which alerts you if something is wrong and outside normal parameters.

I know when my t-stat was bad it wasn't until I came here that I found out. I thought it was fine at 165* driving down the road with a lead foot.

It probably wasn't bad but may have been getting there. Again, a scan tool would tell you if the thermostat was sticking or if the CTS was bad. Due to the nature of having to remove the alternator it's not a bad idea to change both thermostat and CTS at the same time given the CTS's relatively cheap price.

I'm still learning the mechanical side of things with being a vehicle owner, so diagnosing possible issues is still new to me. I wanted to buy a tech 2 scanner, but the 1k(Ebay) price range is a bit steep for me lol

There is no reason to go full out and buy a Tech2. A sub-$100 scan tool is all you will need. Just make sure it provides the coolant temp.

 

[CaptainXL]

Replace the fan clutch and do the waterpump while you are at it. Had similar issue and that is the fix

Invest in a scanguage as well. You can see real temps and read and remove codes. Money well spent.

Maybe not a bad idea given the age of her vehicle. A little preventative maintenance goes a long way. And by the way...cooling system issues ARE the leading cause of engine failure.

Scanqauges are not a bad option.

Looks like you could end up spending around $500 for all of this.

 

[HARDTRAILZ]

Scanguage 150
Pump 25-30
Clutch 100

Or 80 for 08 fanclutch and have pcmforless do a tune and remove codes for 150 and have a better setup.

 

[CaptainXL]

Scanguage 150
Pump 25-30
Clutch 100

Or 80 for 08 fanclutch and have pcmforless do a tune and remove codes for 150 and have a better setup.

Being curious I found and AC Delco water pump for $40 with free ship on Amazon.

Amazon.com: ACDelco 252-822 Water Pump Assembly: Automotive

But the AC Delco fan clutches are around $250.

 

[HARDTRAILZ]

Could do e fans cheaper than ac delco then.

I dont generally use delco stuff.

 

[Voymom]

I thought about an E fan setup but would definitely need help with it, as I'm not mechanically experienced as most people here. But it is still an option at the top of my list.

I know water pumps aren't expensive, it's the PITA of changing it that I'm more worried about.

What other scan tools are there that don't cost an arm and a leg to purchase? Brands, types etc.

And doing a PCM4less tune up is also on my list of things to do.

I have a lot going on right now, so money is a bit tight. But I will definitely get the ball rolling and do a bit of searching on e fan kits!

 

[HARDTRAILZ]

Water pump is 5 extra minutes when doing fanclutch.

 

[DFWWIZ]

Do the LS1 e-fans (<$130) swap with Pcm For Less harness for $75 and pick up a few more HP in the change. You will have to program the ECM also. It sure frees up alot more room up front.

 

[CaptainXL]

Water pump is 5 extra minutes when doing fanclutch.

Since were at it...might as well do an electric water pump. Hehe

 

[fishguy1123]

As far as your "short" trips to school/work go, until the temp comes up to normal operateing range I think it will run rich. So your mpg's will suffer simply because it's a short run that's repeated alot. For that matter I can let mine warm up for a few minutes and watch the dic ave. econ drop simply because it's running but not moveing.

 

[Voymom]

As far as your "short" trips to school/work go, until the temp comes up to normal operateing range I think it will run rich. So your mpg's will suffer simply because it's a short run that's repeated alot. For that matter I can let mine warm up for a few minutes and watch the dic ave. econ drop simply because it's running but not moveing.

See that's the problem, there are days when it warms up before I drive out of the neighborhood(despite outside temps) and there are days when it's showing that it's around 170*-180* on the gauge. The temps falls with hard acceleration sometimes...

If it was the fan/fan clutch I thought that it would cause the truck to run warmer than average? I would allow the truck to sit and warm up, but it would take about 45 min even in warm weather to reach the appropriate temp. The MPG's being low with my short trips makes total sense so I won't really worry about that unless it gets beyond stupid lol my main concern now is the mechanics. Once my kids go off to bed, I will be going out to check my water pump.

 

[Chickenhawk]

Before you spend too much money, look at it logically and in order of likelihood.

The thermostat is the likeliest and will seriously impact your mileage. Because you changed it and the temps seemed to come up for a while, we can move on.

Next likeliest is the coolant temp sensor. It doesn't fail instantly; it is an electromechanical sensor exposed to the coolant stream and they will naturally need replacing some day. Also, there is no easy way to determine if your engine is running cool because of a bad thermostat or it only THINKS it is running cool because of a bad coolant sensor. A scan gauge will simply show you what the CTS is reading anyway, and there is only one CTS. Either way, you will run very rich.

Because your gauge is not rock solid, I am seriously suspecting the CTS.

Next up is the fan clutch. As they fail, they cause the fan to turn more. This serves to add unnecessary drag AND it overcools your engine. They usually start to fail when first starting and this could be why it seems to take so long to warm up.

I recommend you DON'T try this, but it is possible to stop the fan blades from spinning with just light pressure from your hand wrapped in a rag or a stick against the fan blade shroud. If the clutch is starting to fail, it will take a lot more pressure to stop the fan blades.

My money is on CTS and/or fan clutch. I would replace both right now and then see what happens.

Good luck and let us know.

 

[rcam81]

Do you have a smart phone? If you do, get an Elm 327 OBD bluetooth device and download the Torque app. The Elm327 is $20.00 and the Torque app is $5.00. You will have all the info you need.

 

[CaptainXL]

Do you have a smart phone? If you do, get an Elm 327 OBD bluetooth device and download the Torque app. The Elm327 is $20.00 and the Torque app is $5.00. You will have all the info you need.

Actually not just any smartphone. You need an Android. Torque is not available for apple iPhone.

 

[Mooseman]

If you have an old Windows Mobile phone laying around, there is the OBD Gauge app for free. Just used it, works great.

OBD Gauge

 

[n0kfb]

>snip<

Now it seems to run right at 210 and sometimes it runs 180/190. It has also been decreasing or cooling off (on the gauge) when we get on the gas, it does eventually get back up to temp, it's just really bothersome as we just changed the t-stat. I plan on putting in a new sensor, and new fuel filter to see if that helps with not only this issue but the rough idle/stalling problem.

>snip<

What other options should I consider in fixing these issues? All fluids have been drained, flushed and refilled as well. Could we possibly be looking at a new t-stat again? And what would cause the t-stat to constantly go bad? I have a feeling there is a bigger underlying issue with this thing, but I have no idea where exactly to start.

Thanks!

With the coolant temp sometimes running a bit low, I'd wonder about the thermostat. How hard is it to replace the thermostat? Is there any special procedure to purge air from the cooling system after you replace the thermostat?

As for rough idle and stalling, does it only happen when the A/C is on? If so, clean your throttle body.

Good luck!

-- Dan Meyer

 

[CaptainXL]

With the coolant temp sometimes running a bit low, I'd wonder about the thermostat. How hard is it to replace the thermostat? Is there any special procedure to purge air from the cooling system after you replace the thermostat?

As for rough idle and stalling, does it only happen when the A/C is on? If so, clean your throttle body.

Good luck!

-- Dan Meyer

That's a good point and can't believe no one brought it up earlier. Check your coolant level. Perhaps you have some air in there causing the tip of the coolant temp sensor to not be submerged in the coolant.

I always warm up the engine fully and fast idle the engine while a friend pours coolant in the radiator neck until no air is left.