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Temp Gauge goes to Overheat while stuck in traffic


kens96

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Sitting in traffic for about 20 minutes creeping about a mile. Outside temp says 62, AC running on and off running set at 68. Temp gauge goes to the second line to the right past center. Start moving and temp creeps down to center and stays there. Stop at the store for 3 minutes, start the car and sit at the light and the same thing happens. Start moving and the temp guage goes to center. Stop for gas, start the car and drive away and the gauge stays at center. Get home and start checking under the hood for a blocked radiator while the car is idling and the temp guage gets to the red and the AC off for engine protection comes on. Shut the car off and check the temp of the engine at the coolant crossover and at the small line that goes back to the reservior and the best i get is196. Turn it back on and race the engine to 1800 for a few seconds and the temp gauge drops right back to center and stays there. With AC on, both fans run constantly at low speed with AC off both stayed on and went in to high speed when the gauge went to the right.

As for recent repairs.

Replaced the crossover housing and water pump. 5 months ago

Replaced waterpump belt 5 months ago

Replaced all the heater core hoses and upper and lower 2 months ago

Radiator is about 2 years old

New Dexcool with Tabs 2 months ago

I've had cars overheat on me in the past and this one does'nt appear to be actually overheating the gauge says it is just after a long idle but once you start moving and or increase RPM it drops to normal very quickly

I'm leaning towards replacing the Coolant Cap or the temp sensor. Has anyone else experienced this?

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Its only been 30 minutes and I was able to pull the cap. There was no pressure and the reservoir is still full the coolant is warm. If I really overheated, wouldn't there be steam and a lot of pressure coming out?

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Have you checked the DTC's? A bad ECT sensor should set a DTC I think. If not, rent the block test kit from AZ and test the coolant for exhaust gases before throwing parts at it. Rule out the HG's first.

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Ken, unless I missed it, have you replaced the thermostat? A thermostat that is binding will be sluggish, but I dont think that if it was hanging up, the temp would go down when you moved, if it was stuck partially closed it is restricting flow, but maybe the increased coolant flow pressure from increased RPM frees the bind. Consider replacing it if its old, just to eliminate it from the equation. You may need to replace the cover with the new style because the cover seal design has changed.

The drop in temp when you move could be the cooling fans, are both fans running on high? Check for a dragging fan, I had a fan that was freewheeling with no torque or high rpms.

I am sure that you checked the purge line, air in the system will cavitate and stop coolant flow and increases RPM may suck more coolant.

Are you misfiring in the morning? Smell the coolant in the coolant tank and see if you have an exhaust smell.

You checked codes right?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Hi Mike. I checked for codes and there are none. I will check the purge line. I did this last year and it was fine but it was before the the waterpump and crossover installation that was done at the dealer so it might be blocked. Once the coolant gets to temperature I am seeing flow in the reservoir and when I run up the throttle I see the coolant level drop and return at idle. No misfiring car runs great. Don't know how old the thermostat is. Good point! For grins I bought a new reservoir cap and compared it to my old one. the rubber on the old one had swelled quite a bit. Just went out for a spirited run with the new cap and then let it idle in the garage with AC off. Best the needle moved was its own width to the right. Leaving it overnight to see if it holds pressure.

Ranger - I tried to get the combustion gas kit at Advance Auto but they don't have it. Will check O Reillys and AutoZone. I do have a HG question. If it was the head gasket and the engine really overheated, wouldn't driving it at speed or harder make it overheat more? In my case when I get to regular driving speeds, the temp gauge drops to normal.

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This does not appear to be HG symptoms to me. Change thermostat and check purge line and fans.... I will say this, my engine needs HGs before I stopped driving it it got to the point where hitting traffic after a high speed run would overheat it quickly up to 230 to 240, when I would get going again it would not go down below 217, it kind of stayed hot, and got progressively hotter. Plus I have a miss for 5 minutes every morning and if I monitor real time misfires, I have slight misfires on 2 cylinders all the time that does not set a misfire code

You are not setting a misfire code that is good

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thanks Mike I will change the thermostat. Do I need to go AC Delco or can I go after market? If its AC Delco then i need to hit the Caddy Dealer early tomorrow. Parts department is only open for a few hours.

BTW Its been over an hour and the system still has pressure. Pulled the cap and heard air release and some gurgling so it appears the purge lines are working. Coolant level is good.

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did you say if your fans run when the temp gauge reads hot? seems to me the fans will run with the a/c on. if coolant is circulating and fans are running, it would be very hard to overheat at 68F temp.

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Joeb,

Fans are running with the AC on and turn on when the guage goes to above normal temp. They are not free wheeling. I agree with you I shouldn't overheat, but I don;t think i'm really overheating because when I rev the engine the temperature goes back to normal and does this quickly. A partially open thermostat or a blockage does make sense.

Don't want to throw parts at this, but has anyone had a flakey temperature sensor that once it is exposed to warmer than normal coolant the signal runs away to make the gauge read hot even though it isn't?

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Sounds like a hose or radiator blockage to me. Check for leaves between the A/C condenser and the radiator.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I had the same problem (coolant was tested on exhaust gases => everything okay).

The temp gauge went just a litte bit to the right when I was stuck in traffic unless I increased the rpm to more than 1000... when I did than, it went back to normal pretty fast.

I don't know what it could be, but I did nothing and it didn't happen again for about 2 months now. Maybe there was air in the cooling system, because it happend directly after I had changed the radiator and the coolant. Some weeks later => no problems any more and the coolant is at the correct level when cold.

How can I remove air from the cooling system at my Northstar? The BMW has a litte screw to do this, let the car get warm in idle and when the thermostat opens I can open this screw and the air in the system can go out... when there are no bubbles any more and only water comes out, the system has no air in it any more.. perfect sollution :) Is there such a screw at ma Northstar? Couldn't find anything...

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I second what BBF said. Make sure the air purge line is clear. You can take a Mityvac Vacuum/Pressure Pump and use it to suck out any debris. I had an overheating problem with my '94 Eldorado and cleared the purge line and it fixed it. I'm not saying that this is definitely what is causing your overheating problem, but it's something to consider. If head gaskets are good then it could also be a thermostat problem or perhaps the radiator is clogged up?!

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Where or what is the air purge line? Maybe I should check it on my car as well, but I'm not sure where to search for it?! :)

I think it could be, that air in the cooling system could cause this litte overheating issue while you're stuck in traffic... I would try to vent the cooling system at first, especially if you have refilled the cooling system recently.

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crossover housing? the big cast aluminum item? never heard of those being replaced. the coolant sensor is screwed into the housing. under the throttle linkage. almost impossible to see. just follow a small electrical lead to it. do you know how to set the DIC to display engine temp? not that it should be different from the gauge.

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Thanks Mike I will change the thermostat. Do I need to go AC Delco or can I go after market? If its AC Delco then i need to hit the Caddy Dealer early tomorrow. Parts department is only open for a few hours.

BTW Its been over an hour and the system still has pressure. Pulled the cap and heard air release and some gurgling so it appears the purge lines are working. Coolant level is good.

Your diagnostics here do not prove that the purge line is clear. Pulling the hose off of the tank while the engine is idling is a proof, make sure the coolant is not hot, and dont face it toward the fender's painted surface. For the hell of it, disconnect the rubber hose from the "bolt with a hole in it" take a wrench and remove the "bolt with a hole in it" very carefully, and look through it, find a drill bit or pipe cleaner and push it through to clean it out.

Keep in mind that you recently did cooling system work, maybe the tablets congealed at the orfice, just a thought, Id have a look

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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The purge line is how the air gets out of a Northstar system. It's also used in keeping the surge tank water close in temperature to the rest of the coolant temperature. It's a 3/8" rubber hose that goes from the water pump to the bottom of the surge tank. Because of this feature, the Northstar doesn't need a little screw for bleeding air like the BMW because all the air ends up in the surge tank below the radiator cap, where it is bled off as the coolant expands when the engine warms up.

The Northstar cooling system is radically different from those of all cars before about 1990. I think it was one of the first to do things this way.

OLD STYLE: Cooling systems since cars went to water cooling worked like this:

  • Water from water pump enters the block. Usually the water pump has two outlets for V engines.
  • Water from the block flows through the head gasket interface to the head and cools the head and valve stems (or just the head, for flathead engines).
  • Water exits the head through the thermostat, which may be on an assembly that takes water from both heads for the thermostat (this is usually part of the intake manifold for V8 engines). A small by-pass goes from near the thermostat input back to the water pump input. Heater hose water flow usually parallels the by-pass flow.
  • Water from the thermostat enters the radiator.
  • Water exits the radiator to the input of the water pump.
  • Pressure is regulated by a calibrated pressure relief built into the radiator cap, with overflow routed through a rubber hose to under the car. Cars with a surge tank route the overflow there, instead, and the water is pulled back into the radiator as the engine cools.
NORTHSTAR: The Northstar and the reverse-flow system used in the LS engines and others nowadays works like this (from the 1997 FSM pp 6-196-197):

  • Water from the radiator passes through the thermostat and enters the water pump.
  • Water enters both sides of the block through a manifold (the cross-over on the Northstar).
  • Water flows through the head gasket interface to the heads.
  • Water cools the heads, valve stems, and cam.
  • Water flows out of the heads back to the crossover, to the output radiator hose fitting and across the thermostat temperature-sensing part at the water pump input.
  • The bypass to the surge tank, the heater hoses, and the throttle body heater circuit are parallel paths from the crossover at the engine output, through the [surge tank | heater core | throttle body heater] to the water pump input. This is also parallel to the radiator/thermostat path.
  • Water flows through the radiator back to the water pump input.
  • Temperature regulation is achieved by passing the hot engine water output across the temperature-sensing part of the thermostat. The thermostat "sees" mixed radiator and engine water, thus the temperature of the water as it enters the water pump.
  • The surge tank is pressurized and its output goes to the heater output hose through a T-connector and back to the water pump input.
There are two major differences between the old system and the new system. First, the thermostat is at the inlet of the water pump and regulates the temperature of the water entering the engine, not exiting the engine. This means that we are back to 180 F thermostats instead of 195 F thermostats to maintain the engine temperature at around 200 F. Second, the volume of the water pump is much higher and maintains the overall engine temperature more uniformly, particularly when the engine is under load and putting out a lot of heat.

The location and flow of the surge tank is explicitly designed to incorporate purge of system air as part of normal operation (FSM, p. 6-197, next-to-last paragraph).

But I digress. Your symptoms look like a lack of cooling at idle RPM. This likely has one of two causes: clogged radiator air path (look for leaves matted on the radiator or A/C condenser), or clogged radiator. I'm not mentioning the fans because you have already checked those.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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How can I get the DIC to display my coolant temp?
This is done by changing the override code IPS05 in the IPC module. This process is described in the 1997 FSM pages 8C1-19 through 8C-21. See "IPC Override Displays" on page 8C1-21 for the step-by-step.

The IPS override code IPS05 is a number from zero to 255. In computer-ese, it's an 8-bit number that controls eight displays on the DIC. A set bit means the data is displayed, a reset bit means it is skipped. According to page 8C1-21, t the factory, analog IPS IPS05 codes are set to 122 (0x7A or 0b0111 1010) and digital displays are set to 43 (0x2B or 0b0010 1011). The values of the bits add up to the code, and have the functions according to this table (see data over FSM page 8C1-21):

IPS05

Bit Value Function

0 1 Instant MPG

1 2 Fuel Used

2 4 MPH

3 8 Avg MPG (typo in FSM; says MPH)

4 16 Engine RPM

5 32 Battery Volts

6 64 Coolant temperature

7 128 NOT USED for IPS05

On the analog display, coolant temperature is enabled in the factory default value of IPS05. In the digital display, you need to add 64 to it, or set it to 107.

Note this very important warning on page 8C1-21:

If any override values are changed and the above procedure is not followed, DTC B1557 may be set. DTC B1557 can not be cleared, this is a non-recoverable condition and the IPC must be replaced. If the OFF button is pressed and the IPC displays the IPC CLEAR CODES message, exit the vehicle diagnostic system and start over. This resets the override options back to their original values and prevents DTC B1557 from setting.

At this point I refer you to your FSM in the Instrument Panel Cluster section. This is because a slip of the finger here can "brick" your IPC module, requiring a very expensive replacement that also involves serious surgery on your dashboard. This essentially falls into "Don't Try This At Home" territory, so I'm not going to post this hazardous procedure for casual DIY's to see.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Well I changed the thermostat and checked all the purge lines. Everything is back together and clear. Filled and purged the system and still had the temp gauge go between the first and second line to the right while it sat idling. Did this with the AC off to check the fans for about 45 minutes. Once the fans kicked into high the temp gauge would drop to close to center. All the time it is idling I am seeing mist coming from the tailpipes. Figure the cats should be hot enough by now to burn off moisture. Temp outside is 58. Take a 20+mile drive with stoplights, with the AC on, and the needle never moves off center. Also the mist from the tailpipes is not appearing while sitting at lights. Drive past NAPA and pick up the coolant combustion test kit. Get home and perform the test and I get a green color (not the yellow they say I should get). This does mean I have combustion gases getting into the coolant. Might be time to let it go, but I'm thinking about continuing to drive it for as long as I can (keeping an container of dexcool premixed in the trunk since I don't have any misfiring and other than the gauge jumping, it still runs great !

Has anybody had a similar situation and can give me an idea of how much more time I might have ?

Edited by kens96
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Ken, did you check the old coolant for gasses, or am I reading that you changed to new coolant, and the tester still turned green?

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1995 STS Crimson Pearl on Black leather

1997 STS Diamond White

1999 STS Crimson Pearl

2001 STS Silver

2003 STS, Crimson Pearl

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I went to the NAPA web site and saw that they have several test kits. These are made by different manufacturers. A few years ago when I had a head leakage problem I went looking for a test kit at a NAPA store, Pep Boys, and elsewhere. I found that they were available on special order but nobody stocked them, because they went bad after a few months on the shelf and they didn't sell quickly. I ended up having a pressure test instead.

You say you changed the thermostat and then did a coolant test with a NAPA kit the same day. A coolant test isn't worth much unless the car has been run without draining the coolant for a few days. The test won't find combustion products in fresh coolant even if there is a head gasket problem.

Here's what I think:

  • A green color instead of a yellow color is not a definitive result.
  • Without further information (NAPA part number, expiration date of the kit, etc.) I can't verify the accuracy of the kit.
  • The problem really doesn't sound like a head gasket. All cars with large exhaust systems have condensation that generates moisture for some time after starting a cold engine, particularly those parked outside in cool or cold weather. This causes steam out the exhaust pipe and even water dripping from the tips. That, and short trips that don't entirely dry out the mufflers, is what rusts out exhaust systems.
Here's what a head gasket problem on a Northstar looks like:

  1. The car starts using coolant. A little at first, then, for a daily driver, a quart a week or more starts to go away for no visible reason.
  2. You pass a truck on an uphill grade, or otherwise give the car a lot of gas at high speed for 20 or 30 seconds or more. About a minute later, the temperature spikes for a few seconds, then drops to normal. If you aren't quick and sharp-eyed, you will miss it.
  3. Overheating after a WOT for more than a second or two at highway speeds will cause increasingly worse temperature spikes, then overheating sessions. After a few months you you must feather-foot it at freeway speeds and slow down on steep grades to avoid overheating.
At no time do you have problems overheating at idle or in traffic, only after stressing the engine. You have never described a temperature spike or overheating problem after nailing it on the highway, which is the definitive characteristic of a Northstar head gasket problem.

I really do NOT think that you have a head gasket problem. If you do, it's far from typical. What I would do if I were in your position:

  • Here's a definitive test, at least after the leakage is pretty bad: After letting the car sit all night, start the car cold and walk around behind it. Smell the exhaust. If it does not have a definite coolant smell, then you don't have a head gasket problem. If it does have a strong smell of coolant, then you are done testing. If you are brave, taste the water dripping off the tips; if it is sweet, it's antifreeze; spit and rinse out your mouth when done.
  • Make sure that the thermostat is an AC/Delco part no. 131128 or equivalent, and the radiator cap is AC/Delco part no. RC81 or equivalent. Make sure that the thermostat isn't put in backward. The thermostat is 180 F, the cap is 15 psi. Aftermarket parts don't always work well.
  • Have the radiator water checked and make sure that it is between 50% and 70% antifreeze (pink, or OAT, not green; somebody correct me if they used green in the 1996 model year). If it's outside that range the car can overheat.
  • Have a good mechanic or a radiator shop do a pressure test. Have them do the coolant test for combustion products, but on coolant that was in the car when it last overheated, not right after working on the cooling system. This will tell you for sure whether or not you have a head gasket problem.
  • Don't forget, check for clogged bypass hose, collapsed radiator hoses, and a clogged radiator.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Ted and Jim.

Thanks for the optimism! Maybe I missed something here is what I did and parts used. The coolant in the car is the same that was in it last night when the temps went high with maybe 1/2 a quart of fresh to top off for spillage. I drained it into a plastic pan that is only used for dexcool and poured it pack into the car. I had replaced all the heater core hoses on 11/22/09 and put 8 quarts of fresh dexcool 50/50 in then so the majority of the coolant is only 2 months old. The thermostat is a new AC Delco part no. 131128 with a new gasket. The cap is a 16lb Slant. The combustion test kit is NAPA BK.700-1006 made by Balkamp Inc. There is no expiration date on the box or the bottle of fluid. The fluid is a brilliant blue color. All the purge lines and bolt hole flow freely. I was getting erratic flow from the purge line to the reservoir until all the air was relieved. Jim you are correct that none of the symptoms indicate a blown head gasket. from reading some posts and Google search for combustion gases in coolant, I do seem to have the symptoms for that as it relates to erratic temps gauge swings being normal at driving speeds but heating up in traffic. I'm hoping you are correct and it is not the HG. The car still runs and drives great.

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What I forgot... The temp gauge got a little higher, when I drove uphill for longer distances (gauge at about 2 o'clock, not far away from middle position).

But when I drove downhill the temp gauge showed me 10 o'lock, a little lower temp than normal. How do you explain that?

(after driving on the highway with about 120-130mph - all with normal temp - the temp gauge also showed me a little lower temp than normal while I was decreasing the speed and quickly went back to normal)

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