please Help With This Confusing Sierra!

[cav13]

Hey guys, REALLY need your opinions and help here. Recently my 1998 GMC Sierra 4x4 1500 5.7 with 165,000 KMS has stopped warming up to operating temperature.... The heater still blows nice hot air.. I have tried 2 195 degree thermostats... as well as 3 different CLUTCHES for the cooling fan. Basically you can have the car idle for an hour and it will not go over 55-60 degrees celcius.. The only way I can get it to reach the operating temperature is remove the front fan completely. The trucks coolant seems nice and clean basically because its brand new. On a side note, the engine light is on and it has been diagnosed that the BANK 2 sensor is below threshold.. Does anyone have any ideas what the problem could be?

[asc08]

I would check the temperature of the coolant, with an independent thermometer, either in the top of the radiator (of course do not open the radiator after the truck is already warm), or with a non-contact temperature sensor, on one of the radiator hoses.

 

I suspect that either your gauge is reading incorrectly, or the temperature sensor is bad, but be sure to check things out before you start replacing parts.

[cav13]

Thanks for the quick reply. As a matter of fact we have tried that too. Our original assumption was the gauge was wrong. However, our thermometer we stuck in there read exactly what the gauge was reading in the truck. 50-60celcius. Another note, when we remove the front cooling fan altogether, it shows the engine get up to normal operating temperature and we can feel the rad hose pressurize with hot fluid once the thermostat opens.

 

 

 

I would check the temperature of the coolant, with an independent thermometer, either in the top of the radiator (of course do not open the radiator after the truck is already warm), or with a non-contact temperature sensor, on one of the radiator hoses.

 

I suspect that either your gauge is reading incorrectly, or the temperature sensor is bad, but be sure to check things out before you start replacing parts.

[LCPullman]

Has the engine been running fine (i.e. smoothly, not roughly)? So would you say that the thermostat never opens when the temp stays low?

[cav13]

Yea the engine runs smoothly. It idles around 600 RPM(Dont know if that is what its supposed to be or not) the thermostat is not opening at all we checked it often and the rad hose running to it is never hot or hard from pressure. however again when we took the front fan off, thermostat opened, hose got hard and HOT. Only other thing is i get roughly 350-385kms a tank of gas. sounds a little low to me. I dont notice a coolant leak at all...

 

 

Has the engine been running fine (i.e. smoothly, not roughly)? So would you say that the thermostat never opens when the temp stays low?

[[email protected]]

I'm with the others, if the heat still blows hot, then the cts for the gauge has went out. That's how they fail,they start indicating less temp than what it really is.

[LCPullman]

Yea the engine runs smoothly. It idles around 600 RPM(Dont know if that is what its supposed to be or not) the thermostat is not opening at all we checked it often and the rad hose running to it is never hot or hard from pressure. however again when we took the front fan off, thermostat opened, hose got hard and HOT. Only other thing is i get roughly 350-385kms a tank of gas. sounds a little low to me. I dont notice a coolant leak at all...

 

If the thermostat isn't opening, then its doesn't seem it should be a gauge problem because the thermostat has nothing to do with the temp sensor or gauge.

Now, low gas mileage would make some sense, because I think that the engine usually runs richer until the coolant temp comes up, and if its not coming up, then it will keep running rich - also on my 93, the TC doesn't lock until the temp is up.

 

The only effect I can see taking the fan off would make is to reduce drag on the pulley system and the water pump - (this assumes the thermostat isn't open and thus no coolant is being circulated through the radiator.)

 

Was the idle RPM the same with the fan off?

Did you put the fan back on and confirm that it is still not heating up?

Also, with the fan on - if you take it out for a good drive like 10 or 15 mi on the highway and then open the hood, does the engine bay seem hot (Normally it should)

[cav13]

Would the guage cause the thermostat not to open though?

 

 

I'm with the others, if the heat still blows hot, then the cts for the gauge has went out. That's how they fail,they start indicating less temp than what it really is.

[cav13]

Well after 40 minutes of idleing with the fan on we noticed the no matter what the truck was not gonna heat up, so we removed the fan and within 3 minutes boom shot up to operating temperature. However i did not make a note about the rpm at that time, i can go outside right now and take the fan off and try again. but when we noticed with the fan off that the engine was starting to get too hot, we quickly turned off the truck, reinstalled the fan, turned the truck back on, and the temperature just dove back down to 50-60 celcius in no time. I have also drove the truck for more then 20 miles with the fan on and the temp still showed the 50-60 celcius range the whole time. however i did not make a note how hot the engine bay was after i turned it off. i will also try that tonight.

 

Yea the engine runs smoothly. It idles around 600 RPM(Dont know if that is what its supposed to be or not) the thermostat is not opening at all we checked it often and the rad hose running to it is never hot or hard from pressure. however again when we took the front fan off, thermostat opened, hose got hard and HOT. Only other thing is i get roughly 350-385kms a tank of gas. sounds a little low to me. I dont notice a coolant leak at all...

 

If the thermostat isn't opening, then its doesn't seem it should be a gauge problem because the thermostat has nothing to do with the temp sensor or gauge.

Now, low gas mileage would make some sense, because I think that the engine usually runs richer until the coolant temp comes up, and if its not coming up, then it will keep running rich - also on my 93, the TC doesn't lock until the temp is up.

 

The only effect I can see taking the fan off would make is to reduce drag on the pulley system and the water pump - (this assumes the thermostat isn't open and thus no coolant is being circulated through the radiator.)

 

Was the idle RPM the same with the fan off?

Did you put the fan back on and confirm that it is still not heating up?

Also, with the fan on - if you take it out for a good drive like 10 or 15 mi on the highway and then open the hood, does the engine bay seem hot (Normally it should)

 

[[email protected]]

Would the guage cause the thermostat not to open though?

 

 

I'm with the others, if the heat still blows hot, then the cts for the gauge has went out. That's how they fail,they start indicating less temp than what it really is.

 

 

no, the thermostat is not electronic, didn't catch that.

[dewfpo]

Which bank 2 sensor is causing the fault?

 

Please don't take this wrong, but are you sure you have the thermostat in the proper direction?

 

DEWFPO

[LCPullman]

Quoted from Here: http://answers.yahoo.com/question/index?qi...04081452AA1k4Zi

 

Another thing,,,

Partial internal blockage of Radiator.

 

Crossflow radiators stop-up from Bottom Up,,,

This has the effect of "Shortening" the Radiator's Height,,

But it Also Repositions the CENTER of the Radiator Core in relation to Fan Clutch's thermal sensor.

 

Result is,,,

and engine begins to come up to Operating temp,,

You get an unusual concentration of heat,,,so to speak.

 

The airflow across the rad core makes the Fan Clutch THINK it's hotter than it actually is.

 

So,,Fan Clutch engages into full cooling mode while engine is still actually cold.

 

You should be able to Hear/Feel if Fan Cluch is engaged,,and fan is roaring hard & pushing a bunch of air.

 

Switch engine OFF,,,and FEEL how much resistance there is to turn the fan blades.

At 160's it oughta darn near be free-wheeling.

 

You can sorta "X-Ray" your radiator and get a rough idea of any internal blockage pattern.

 

-Run it till it's hot,,,

Spray radiator with a hose.

Use a Good Light to see where the Water Evaporates immediately versus any areas of the Fins where it Stays Wet.

 

The HOT places which have good coolant flow will Dry near Instantly,,,

Any "Cold Places " where Coolant is blocked from flowing will remain wet.

 

Partial Blockage on anything 5~7 yrs old or more is almost universal.

But radiators are Big enough to accomodate a lot of blockage.

 

USUALLY a clogged up radiator will give off Too Little Heat,,

causing Fan Clutch to remain OFF.

So engine Overheats from Fan not engaging.

 

Which is all OPPOSITE of your situation.

 

But OCCASIONALLY,,,,

Clogged Lower Tubes raise to Flow Higher in the Core.

And it's the "Hottest" Water returned from engine.

 

Instead of getting Dispersed thru entire core and losing a bit of heat before getting to Fan Clutch area....

More of it goes more directly thru the tubes nearer the Clutch.

 

Makes a concentrated Hot Spot which tricks fan into engaging.

Radiator then returns Overly cool water to engine.

 

It happens,,,but it's RARE,,and it's TRICKY to determine.

 

Try measuring Temp on FAN CLUTCH after shutting down,,,,

compared to Lower Corner of radiator on the side Opposite of water inlet.

 

Or,even easier/simpler,,

Block Radiator with a piece of Cardboard.

Try to put it between Fan & Radiator,,,,and not just in Front of Radiator....to more fully Isolate fan's airflow .

CAREFULLY & SECURELY(sorry,,just HAD to say that reminder:)

 

See what idle temps ya get with "No Airflow"...

which is more like Normal Conditions until full temp is reached.

 

One other thing,,,and it probably doesnt apply here....

"Heavy Duty" and "Extra Cooling" Fan Clutchs engage Very early in temp scale.

They're rated in terms of "Percentage of Drive Rotation"

They'll spin much closer to actual INPUT RPM ,,,rather than slipping more and running far Underspeed like "standard" fan clutches do.

 

 

None of the above may be any use whatsoever,,,but when ya run outa Normal Things to troubleshoot,,,,it's just a couple ideas you may wanna check out.

 

When COOLING TOO WELL gets beyond simply "Stuck Open Thermostat" problems,,,picken's get pretty slim.

[cav13]

ok, so i went to go get gas, since i have been using so much... got 200 kms on 60$ of gas. how said. so i let the truck warm up as far as it will go with the fan on. (50-60) made a precise note of the idle speed which was 700rpm. so then i stop the truck, pull the fan off, turn the truck on, wait 5 minutes until it reaches operating temp and the thermostat opens. made another precisde note of the rpms which was 700rpm. so i get 700rpm with the fan on and with the fan off.. dont really know if that helps u guys with anything.. i might try to do the covering the enitre radiator front and back as stated in the above post see what that does. Oh and by the way, 60 bucks only gave me 50 liters which is about 13 gallons

Quoted from Here: http://answers.yahoo.com/question/index?qi...04081452AA1k4Zi

 

Another thing,,,

Partial internal blockage of Radiator.

 

Crossflow radiators stop-up from Bottom Up,,,

This has the effect of "Shortening" the Radiator's Height,,

But it Also Repositions the CENTER of the Radiator Core in relation to Fan Clutch's thermal sensor.

 

Result is,,,

and engine begins to come up to Operating temp,,

You get an unusual concentration of heat,,,so to speak.

 

The airflow across the rad core makes the Fan Clutch THINK it's hotter than it actually is.

 

So,,Fan Clutch engages into full cooling mode while engine is still actually cold.

 

You should be able to Hear/Feel if Fan Cluch is engaged,,and fan is roaring hard & pushing a bunch of air.

 

Switch engine OFF,,,and FEEL how much resistance there is to turn the fan blades.

At 160's it oughta darn near be free-wheeling.

 

You can sorta "X-Ray" your radiator and get a rough idea of any internal blockage pattern.

 

-Run it till it's hot,,,

Spray radiator with a hose.

Use a Good Light to see where the Water Evaporates immediately versus any areas of the Fins where it Stays Wet.

 

The HOT places which have good coolant flow will Dry near Instantly,,,

Any "Cold Places " where Coolant is blocked from flowing will remain wet.

 

Partial Blockage on anything 5~7 yrs old or more is almost universal.

But radiators are Big enough to accomodate a lot of blockage.

 

USUALLY a clogged up radiator will give off Too Little Heat,,

causing Fan Clutch to remain OFF.

So engine Overheats from Fan not engaging.

 

Which is all OPPOSITE of your situation.

 

But OCCASIONALLY,,,,

Clogged Lower Tubes raise to Flow Higher in the Core.

And it's the "Hottest" Water returned from engine.

 

Instead of getting Dispersed thru entire core and losing a bit of heat before getting to Fan Clutch area....

More of it goes more directly thru the tubes nearer the Clutch.

 

Makes a concentrated Hot Spot which tricks fan into engaging.

Radiator then returns Overly cool water to engine.

 

It happens,,,but it's RARE,,and it's TRICKY to determine.

 

Try measuring Temp on FAN CLUTCH after shutting down,,,,

compared to Lower Corner of radiator on the side Opposite of water inlet.

 

Or,even easier/simpler,,

Block Radiator with a piece of Cardboard.

Try to put it between Fan & Radiator,,,,and not just in Front of Radiator....to more fully Isolate fan's airflow .

CAREFULLY & SECURELY(sorry,,just HAD to say that reminder:)

 

See what idle temps ya get with "No Airflow"...

which is more like Normal Conditions until full temp is reached.

 

One other thing,,,and it probably doesnt apply here....

"Heavy Duty" and "Extra Cooling" Fan Clutchs engage Very early in temp scale.

They're rated in terms of "Percentage of Drive Rotation"

They'll spin much closer to actual INPUT RPM ,,,rather than slipping more and running far Underspeed like "standard" fan clutches do.

 

 

None of the above may be any use whatsoever,,,but when ya run outa Normal Things to troubleshoot,,,,it's just a couple ideas you may wanna check out.

 

When COOLING TOO WELL gets beyond simply "Stuck Open Thermostat" problems,,,picken's get pretty slim.

 

[cav13]

ok, well i drove the truck for an hour straight at around 65 mph. temperature guage never went over 60Celcius. The heat from the vents comes out scolding hot. I finish my drive and quckly pop he hood, take the rad cap off and drop a long thermometer in it and it registers around 50Celcius... How does the coolant get that warm if the coolant doesnt seem to be circulating through the thermostat? and if it was circulating the coolant temperature should be a lot hotter no?

 

ok, so i went to go get gas, since i have been using so much... got 200 kms on 60$ of gas. how said. so i let the truck warm up as far as it will go with the fan on. (50-60) made a precise note of the idle speed which was 700rpm. so then i stop the truck, pull the fan off, turn the truck on, wait 5 minutes until it reaches operating temp and the thermostat opens. made another precisde note of the rpms which was 700rpm. so i get 700rpm with the fan on and with the fan off.. dont really know if that helps u guys with anything.. i might try to do the covering the enitre radiator front and back as stated in the above post see what that does. Oh and by the way, 60 bucks only gave me 50 liters which is about 13 gallons

Quoted from Here: http://answers.yahoo.com/question/index?qi...04081452AA1k4Zi

 

Another thing,,,

Partial internal blockage of Radiator.

 

Crossflow radiators stop-up from Bottom Up,,,

This has the effect of "Shortening" the Radiator's Height,,

But it Also Repositions the CENTER of the Radiator Core in relation to Fan Clutch's thermal sensor.

 

Result is,,,

and engine begins to come up to Operating temp,,

You get an unusual concentration of heat,,,so to speak.

 

The airflow across the rad core makes the Fan Clutch THINK it's hotter than it actually is.

 

So,,Fan Clutch engages into full cooling mode while engine is still actually cold.

 

You should be able to Hear/Feel if Fan Cluch is engaged,,and fan is roaring hard & pushing a bunch of air.

 

Switch engine OFF,,,and FEEL how much resistance there is to turn the fan blades.

At 160's it oughta darn near be free-wheeling.

 

You can sorta "X-Ray" your radiator and get a rough idea of any internal blockage pattern.

 

-Run it till it's hot,,,

Spray radiator with a hose.

Use a Good Light to see where the Water Evaporates immediately versus any areas of the Fins where it Stays Wet.

 

The HOT places which have good coolant flow will Dry near Instantly,,,

Any "Cold Places " where Coolant is blocked from flowing will remain wet.

 

Partial Blockage on anything 5~7 yrs old or more is almost universal.

But radiators are Big enough to accomodate a lot of blockage.

 

USUALLY a clogged up radiator will give off Too Little Heat,,

causing Fan Clutch to remain OFF.

So engine Overheats from Fan not engaging.

 

Which is all OPPOSITE of your situation.

 

But OCCASIONALLY,,,,

Clogged Lower Tubes raise to Flow Higher in the Core.

And it's the "Hottest" Water returned from engine.

 

Instead of getting Dispersed thru entire core and losing a bit of heat before getting to Fan Clutch area....

More of it goes more directly thru the tubes nearer the Clutch.

 

Makes a concentrated Hot Spot which tricks fan into engaging.

Radiator then returns Overly cool water to engine.

 

It happens,,,but it's RARE,,and it's TRICKY to determine.

 

Try measuring Temp on FAN CLUTCH after shutting down,,,,

compared to Lower Corner of radiator on the side Opposite of water inlet.

 

Or,even easier/simpler,,

Block Radiator with a piece of Cardboard.

Try to put it between Fan & Radiator,,,,and not just in Front of Radiator....to more fully Isolate fan's airflow .

CAREFULLY & SECURELY(sorry,,just HAD to say that reminder:)

 

See what idle temps ya get with "No Airflow"...

which is more like Normal Conditions until full temp is reached.

 

One other thing,,,and it probably doesnt apply here....

"Heavy Duty" and "Extra Cooling" Fan Clutchs engage Very early in temp scale.

They're rated in terms of "Percentage of Drive Rotation"

They'll spin much closer to actual INPUT RPM ,,,rather than slipping more and running far Underspeed like "standard" fan clutches do.

 

 

None of the above may be any use whatsoever,,,but when ya run outa Normal Things to troubleshoot,,,,it's just a couple ideas you may wanna check out.

 

When COOLING TOO WELL gets beyond simply "Stuck Open Thermostat" problems,,,picken's get pretty slim.

 

 

[69camarorag]

This may sound over simplified, but have you checked the coolant strenght? We have seen issues with coolant being TOO concentrated and not being able to displace the heat. Coolant should be not much more than 50/50 mix. Just a shot inthe dark.