irratic temperature gauge

[turbosts]

Hi,

Thanks for letting me post, new to this forum.

I own a 2000 cadillac sts seville approx, 78k on it. overheated the northstar about two months ago to find a bad coolant sensor which stopped the fans from working, since then replaced water pump, coolant sensor,thermastat, belts ,tensioner, hoses, purge hose,intake manifold and gaskets, checked for vacuum leaks, cylinder compression, leak tests exhaust in the coolant, almost everything i could think of.the problem is that the temp gaughe gets erratic, mostly at 12 oclock then creeps up till i get and engine hot a/c off on the dic.i checked the actual temp and it is normal, if i rev to 3000 rpm during this message it will snap back to normal on the gauge.any ideas where i should check. most of the codes that came up are history, but gets a pcm po171 0r pcm po po131 current at times. also checked for vacuum leaks, none. any help will be greatly aprreciated , it also runs strong idles great, and no steam from the pipes. coolant always full.

[BodybyFisher]

Hi,

Thanks for letting me post, new to this forum.

I own a 2000 cadillac sts seville approx, 78k on it. overheated the northstar about two months ago to find a bad coolant sensor which stopped the fans from working, since then replaced water pump, coolant sensor,thermastat, belts ,tensioner, hoses, purge hose,intake manifold and gaskets, checked for vacuum leaks, cylinder compression, leak tests exhaust in the coolant, almost everything i could think of.the problem is that the temp gaughe gets erratic, mostly at 12 oclock then creeps up till i get and engine hot a/c off on the dic.i checked the actual temp and it is normal, if i rev to 3000 rpm during this message it will snap back to normal on the gauge.any ideas where i should check. most of the codes that came up are history, but gets a pcm po171 0r pcm po po131 current at times. also checked for vacuum leaks, none. any help will be greatly aprreciated , it also runs strong idles great, and no steam from the pipes. coolant always full.

P0131 - Heated Oxygen Sensor (HO2S) Circuit Low Voltage Bank 1 Sensor 1

P0171 - Fuel Trim System Lean Bank 1

Post your history codes also

How did you check the actual temperature?

Is your purge line clear, maybe you are cavitating

[JimD]

You have thrown a lot of parts at this condition. Among them the purge line.

But did you check for a flow of coolant at the reservoir end of the purge line? What you are describing sort of sounds like a blocked purge line and the most common blockage point is the hollow bolt that is threaded into the crossover near the water pump.

Be sure the entire purge plumbing path is free of obstruction.

[BodybyFisher]

GMTA Jim! Happy New Year

[JimD]

GMTA Jim! Happy New Year

And to you, Mike.

[turbosts]

You have thrown a lot of parts at this condition. Among them the purge line.

But did you check for a flow of coolant at the reservoir end of the purge line? What you are describing sort of sounds like a blocked purge line and the most common blockage point is the hollow bolt that is threaded into the crossover near the water pump.

Be sure the entire purge plumbing path is free of obstruction.

i changed the purge line and blew compressed air in it to see the flow com from the recovery tank,yes i threw alot into this repair but had symptoms that warranted my replacements. also i changed both o2 sensors because it was an overheating antifreeze issue i wanted to cover all the bases. i had many codes, but the current ones i was concerned about since theses cars code if you even fart.lol

[turbosts]

Hi,

Thanks for letting me post, new to this forum.

I own a 2000 cadillac sts seville approx, 78k on it. overheated the northstar about two months ago to find a bad coolant sensor which stopped the fans from working, since then replaced water pump, coolant sensor,thermastat, belts ,tensioner, hoses, purge hose,intake manifold and gaskets, checked for vacuum leaks, cylinder compression, leak tests exhaust in the coolant, almost everything i could think of.the problem is that the temp gaughe gets erratic, mostly at 12 oclock then creeps up till i get and engine hot a/c off on the dic.i checked the actual temp and it is normal, if i rev to 3000 rpm during this message it will snap back to normal on the gauge.any ideas where i should check. most of the codes that came up are history, but gets a pcm po171 0r pcm po po131 current at times. also checked for vacuum leaks, none. any help will be greatly aprreciated , it also runs strong idles great, and no steam from the pipes. coolant always full.

P0131 - Heated Oxygen Sensor (HO2S) Circuit Low Voltage Bank 1 Sensor 1

P0171 - Fuel Trim System Lean Bank 1

Post your history codes also

How did you check the actual temperature?

Is your purge line clear, maybe you are cavitating

I think its clear, i changed it and blew compressed air thru it. i changed most of these parts because i had the car dismantled and figured i wanted to kinda nip this in a bud, but didnt. im really needing help on this cause i think i covered anything that would cause this issue.all the pros claim head gaskets but its runs too strong and idles sweet, and the compression is there also the leak test showed nothing. there is no exhaust gases in the antifreeze either, and tail pipes are clean, no smoke except normal condensation. i even retorqued the head bolts none stripped all good.

[turbosts]

Hi,

Thanks for letting me post, new to this forum.

I own a 2000 cadillac sts seville approx, 78k on it. overheated the northstar about two months ago to find a bad coolant sensor which stopped the fans from working, since then replaced water pump, coolant sensor,thermastat, belts ,tensioner, hoses, purge hose,intake manifold and gaskets, checked for vacuum leaks, cylinder compression, leak tests exhaust in the coolant, almost everything i could think of.the problem is that the temp gaughe gets erratic, mostly at 12 oclock then creeps up till i get and engine hot a/c off on the dic.i checked the actual temp and it is normal, if i rev to 3000 rpm during this message it will snap back to normal on the gauge.any ideas where i should check. most of the codes that came up are history, but gets a pcm po171 0r pcm po po131 current at times. also checked for vacuum leaks, none. any help will be greatly aprreciated , it also runs strong idles great, and no steam from the pipes. coolant always full.

P0131 - Heated Oxygen Sensor (HO2S) Circuit Low Voltage Bank 1 Sensor 1

P0171 - Fuel Trim System Lean Bank 1

Post your history codes also

How did you check the actual temperature?

Is your purge line clear, maybe you are cavitating

I think its clear, i changed it and blew compressed air thru it. i changed most of these parts because i had the car dismantled and figured i wanted to kinda nip this in a bud, but didnt. im really needing help on this cause i think i covered anything that would cause this issue.all the pros claim head gaskets but its runs too strong and idles sweet, and the compression is there also the leak test showed nothing. there is no exhaust gases in the antifreeze either, and tail pipes are clean, no smoke except normal condensation. i even retorqued the head bolts none stripped all good.

checked temp at thermastat housing plug with a gauge 206 idling with ac on tried to heat it up but it was fine, only pegged gauge when driven, also replaced recovery tank cap.

[turbosts]

You have thrown a lot of parts at this condition. Among them the purge line.

But did you check for a flow of coolant at the reservoir end of the purge line? What you are describing sort of sounds like a blocked purge line and the most common blockage point is the hollow bolt that is threaded into the crossover near the water pump.

Be sure the entire purge plumbing path is free of obstruction.

hey jim, i did throw alot of parts at this issue but at the time of dismantle i wanted to make sure i covered everything.purge line was clean and blew air into it also got flow from the recovery tank end, i also did the o2 sensors from any antifreeze issue. recovery tank cap too.

[BodybyFisher]

Hi,

Thanks for letting me post, new to this forum.

I own a 2000 cadillac sts seville approx, 78k on it. overheated the northstar about two months ago to find a bad coolant sensor which stopped the fans from working, since then replaced water pump, coolant sensor,thermastat, belts ,tensioner, hoses, purge hose,intake manifold and gaskets, checked for vacuum leaks, cylinder compression, leak tests exhaust in the coolant, almost everything i could think of.the problem is that the temp gaughe gets erratic, mostly at 12 oclock then creeps up till i get and engine hot a/c off on the dic.i checked the actual temp and it is normal, if i rev to 3000 rpm during this message it will snap back to normal on the gauge.any ideas where i should check. most of the codes that came up are history, but gets a pcm po171 0r pcm po po131 current at times. also checked for vacuum leaks, none. any help will be greatly aprreciated , it also runs strong idles great, and no steam from the pipes. coolant always full.

P0131 - Heated Oxygen Sensor (HO2S) Circuit Low Voltage Bank 1 Sensor 1

P0171 - Fuel Trim System Lean Bank 1

Post your history codes also

How did you check the actual temperature?

Is your purge line clear, maybe you are cavitating

I think its clear, i changed it and blew compressed air thru it. i changed most of these parts because i had the car dismantled and figured i wanted to kinda nip this in a bud, but didnt. im really needing help on this cause i think i covered anything that would cause this issue.all the pros claim head gaskets but its runs too strong and idles sweet, and the compression is there also the leak test showed nothing. there is no exhaust gases in the antifreeze either, and tail pipes are clean, no smoke except normal condensation. i even retorqued the head bolts none stripped all good.

Which way did you blow air through the line with a compressor? I am not sure if you are understanding. Follow the line back to "the bolt with a hole in it', remove the hose and check for an obstruction at this point. NEVER try to clear the purge line with compressed air, if you blow it in a direction away from the the tank, you will only temporarily dislodge any obstruction

The "bolt with a hole in it" is located in the upper right section of this photo next to the upper hose inlet. Tank that hose off, remove the 'bolt with a hole' in it and clear it.

How did you determine there were no combustion by products in your coolant?

[turbosts]

I REMOVED IT OFF THE TANK AN BLEW AIR IN THE HOSE FIGURING IT WOULD CLEAR IT FLUID CAME OUT OF THE NECK OF THE TANK AS I BLEW AIR IN SO I GUESSED IT WAS CLEAR, ALSO USED A TEST SRTIP IN THE COOLANT TO SEE IF ANY OIL, GAS WHERE PRESENT IN THERE IT TURNS PURPLE IF IT NOTICES ANY OF THEM. NONE FOUND LIKE A BLOCK TEST STRIP. PLUS I DID THE OLD NOSE SMELL TEST TOO TO SEE IF I SMELLED ANYTHING AFTER IT COOLED.

[Ranger]

The purge line almost never clogs in the line. It usually clogs at the hollow bolt it is connected to. Check to be sure THAT is clear and thus supplying coolant to the purge line.