99 STS Running Hot
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 99 STS Running Hot in Past Cadillac Vehicle Discussion; My 1999 STS is running very hot. But the thing is it only runs hot at stop lights. If Ikeptp ...
  1. #1
    maiahsdad's Avatar
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    99 STS Running Hot

    My 1999 STS is running very hot. But the thing is it only runs hot at stop lights. If Ikeptp it about 2200 RPM, it doesn't run hot. I'm told that is not a head gasket problem. Can anyone help?

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    Mark C's Avatar
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    Re: 99 STS Running Hot

    Thats not a typical symptom of a headgasket issue, thats more likely an airflow issue caused by fans not running, or a slipping waterpump belt. Headgasket issues mostly show up when the engine is heavily loaded, like when driving up a long hill, or when under heavy acceleration.

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    Submariner409's Avatar
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    Re: 99 STS Running Hot

    Yep ^^^. Coolant flow problem.

    What is the coolant level in the reservoir with the engine cold in the morning ? Half full is proper. Do not check while hot/warm. As Mark Csuggested, check the fan fuse(s) - I believe your car has a maxi-fuse in the secondary underhood box - or was that a year earlier ? Eyeball the water pump drive belt system with the engine idling - anything seem amiss ?

    This is a stretch, but......... the water pump impeller has a shroud - in very few cases this shroud separates from the impeller vanes and pump action suffers. Last resort check because you have to drain the system and remove the pump capsule.

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    Re: 99 STS Running Hot

    Try flushing the dirt and dead bugs out of the condenser.

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    Re: 99 STS Running Hot

    Quote Originally Posted by submariner409 View Post
    Yep ^^^. Coolant flow problem.

    What is the coolant level in the reservoir with the engine cold in the morning ? Half full is proper. Do not check while hot/warm. As Mark Csuggested, check the fan fuse(s) - I believe your car has a maxi-fuse in the secondary underhood box - or was that a year earlier ? Eyeball the water pump drive belt system with the engine idling - anything seem amiss ?

    This is a stretch, but......... the water pump impeller has a shroud - in very few cases this shroud separates from the impeller vanes and pump action suffers. Last resort check because you have to drain the system and remove the pump capsule.
    Hello everyone, sorry I've been away from the forum. Work stuff. But I'm back now.

    The car takes about 20 minutes of driving before it'll run hotter. Tonight, I had to drive in gear 3 in order to get home in the traffic. That kept the temp gauge at the noon mark. This is very frustrating.

    The coolant cold is about halfway. And the temp does climb when climbing the driveway, but not if I'm driving uphill in 3rd (because the engine's turning faster).

    This method of keeping it cool is REALLY frustrating, and cause abnormally high fuel consumption. And the heat will stop blowing hot air as well, but will return to blowing hot air when the temp goes back down. A CarX mechanic (he says they know NOTHING about the old Northstars) said to turn the heat up to 90 degrees and turn the fan down to help the engine cool some while driving. But it only helps so much, if any at all. When temp goes up, heat blows cool air.

    When the temp gauge reaches the 1 O'clock position, the fan will come on. I can't see if this car has one or two, but I definitely see one big one in front of the radiator spinning like crazy when the 1 O'clock position is hit by the temp gauge. And it won't turn off until the gauge is back at the noon position for at least 10 minutes or so. So, the fan's working properly.

    I'm sorry, I don't know what the Water Pump Drive Belt System looks like to check it out. BTW, this water pump was replaced 6 months ago, and I've JUST run out of the waranty by 8 days. And I can't afford to replace it. Seems that it's pumping the fluid, but either not fast enough, or flow is restricted in some way. Also, when I stop the engine and am sitting inside the car quiet, I can hear fluid gurgling as if it's moving from behind the dashboard somewhere. Weird. Like it's draining from somewhere, to somewhere. Maybe it's normal.

    The dealer wants $175 just to check it out, and if I choose to have it repaired by them, they'll credit the $175 to the bill. If not, I've paid them for their inspection. He said it would take about 10 minutes to diagnose once it's in. I cannot afford that. I love and need my car, but I can't afford that.

    Couple of friends have suggested thermostats, and engine or radiator flush (this may by one in the same). I have no clue. Just that this is my only way to work and transporting my children. It's bad enough that the leveling system works whenever IT gets ready. Today=no. Tomorrow.... just maybe.


    ---------- Post added at 02:24 AM ---------- Previous post was at 02:22 AM ----------

    Quote Originally Posted by Ranger View Post
    Try flushing the dirt and dead bugs out of the condenser.
    I'm not sure what or where the condenser is. Is there some manual I can download from somewhere that's not an arm/leg? I'm not a mechanic. And the terms and phrases you guys use often are ones I need to learn.

  7. #6
    01ssreda4 is offline Cadillac Owners Fanatic
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    Re: 99 STS Running Hot

    The condenser is what the air hits as soon as it passes through the front grill. It looks like a radiator. Washing this area thoroughly never hurts on any vehicle. Be sure the engine is cool and not running.

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    Re: 99 STS Running Hot

    Northstar thermostat is very reliable and it should be the very last thing to check. You cannot flush the inside of the engine and you are not having problems because of it.

    Water pump drive belt is located at the rear side of the engine (driver's side near your oil dipstick). There should be only one belt on that side so it should be easy to find. Does everything look good? No funny noises or smell around the belt? Is it spinning well?

    When the heat becomes cold, it means the heater core is airbound. This means you have air in the cooling system and air will not cool down the engine. Water pump will cavitate and will pump air - no circulation leads to overheating. Also that "air" in the system is likely to be so hot; it is going to show you a false temperature gauge reading. Have you checked your purge line for blockage? Pull out the hose that is attached to the top nipple of the coolant tank. Point it towards to the coolant filler neck and start the car. If you have a steady coolant flow, it's good. If not, either the hose and/or the hollow bolt at the other end needs to be cleaned.

    Is the coolant level going down?

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    Re: 99 STS Running Hot

    "One large fan in front" ??? There should be two fans, each about 10" in diameter, in a shroud behind (engine side) the condenser/radiator sandwich.

    The condenser is the "radiator" that cools circulating gaseous refrigerant enough that it can be compressed back to fluid, when it goes through the expansion valve (orifice), changes to gas, and in so doing removes heat from the surrounding metal/air passing through the evaporator in the HVAC stack.

    The actual coolant radiator is behind the condenser.

    The two fans and their shroud attach to the engine side of the radiator - some contortions with a flashlight will reveal the fans.

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    mike5514 is offline Cadillac Owners Enthusiast
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    Re: 99 STS Running Hot

    Check the purge line as advised that is the most likely problem, you probably have a slight leak and it is sucking air upon cool down. Replace the surge tank cap.

    Also rent a pressure tester and a block tester from autozone (deposit only) get these two test out of the way before you put money in the car.Mike

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    Re: 99 STS Running Hot

    And the temp does climb when climbing the driveway
    And the heat will stop blowing hot air as well, but will return to blowing hot air when the temp goes back down.
    Also, when I stop the engine and am sitting inside the car quiet, I can hear fluid gurgling as if it's moving from behind the dashboard somewhere.
    All signs of a failed HG, especially the gurgling sound. That's "air" (or exhaust gases) in the cooling system. Check the purge line as suggested. If it is clear, then get a block test kit and check for exhaust gases in the surge tank.

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    maiahsdad's Avatar
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    Re: 99 STS Running Hot

    Quote Originally Posted by maeng9981 View Post
    Pull out the hose that is attached to the top nipple of the coolant tank. Point it towards to the coolant filler neck and start the car. If you have a steady coolant flow, it's good. If not, either the hose and/or the hollow bolt at the other end needs to be cleaned.
    I don't know where these parts are.

    Quote Originally Posted by maeng9981 View Post
    Is the coolant level going down?
    I add a little about every two weeks if that.

    ----------

    OK. When I locate the purge line, I'll check it. By the sounds of it Ranger, I'm in BIG trouble... I think HG's are VERY expensive. I have another year to pay for the car, and it has 178K miles on it. I wanted it so bad. And now look... I'm in a mess. The leveling system comes on when it gets good and damn ready. So sometimes it's good, and sometimes it's not. And above the rear left wheel, there's rust on the fender. I LOVE this car. I just didn't believe I got a bad one...

  13. #12
    Submariner409's Avatar
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    Re: 99 STS Running Hot

    Annotated coolant reservoir pictures and purge line - click on my username, open my profile. 2 albums in there with pictures of Northstar cooling system parts.

    I can't tell that you even read the earlier posts in this thread, but the "one large fan in front" of the A/C condenser (which is sandwiched to the front of the coolant radiator) is NOT factory stock. Someone has modified this car and its cooling system, probably an attempt to stall off the problems you are now having.

    Even your fan ON/OFF sequence is incorrect for a stock system: The fans normally go to SLOW (with no A/C function set) at 224 degrees. That action lowers coolant temp, and as it reaches 213 the fans stop........still stuck in traffic ??? The same cycle repeats. Once you get clear and begin steady motion the cycle stops until, for some reason, coolant temp once again reaches 224. In 99.999% of FWD Northstar cars, above 30 mph, the fans (without A/C set) never run at all.
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    Re: 99 STS Running Hot

    The coolant or surge tank is where you add coolant.

    A HG replacement is about $2000 - $3000 (or more) depending on where you take it. I know 2 guys up here that do it for about $2000.

    EDIT:
    Oops, Sub beat me to it. Boy, I totally missed that "one large fan" thing.
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    Mark C's Avatar
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    Re: 99 STS Running Hot

    The coolant tank also called the surge tank is where you put the radiator coolant into. The purge line is the 3/8" rubber hose that attaches to the top of the tank and runs across the air intake tube, and attaches to the thermostat housing right behind the waterpump. The purge line purges any air and other non condesable gases out of the coolant so they don't get into the water pump and cause it to become airbound and not circulate water thru the colling system. With the engine cool you take the cap off the surge tank, remove the purge line from the tank and stick it into the opening in the top of the tank where you took the cap off. Start the car and check for a steady stream of water flowing out of the hose, if there isn't any then the purge line is plug with something and needs to be cleared. There is a hollow bolt on the thermostat housing the hose slips over, this is the most likely location for a plug to form.
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    Re: 99 STS Running Hot

    This is excellent. I will check this first thing in the morning. I appreciate the help. One guys told me to get a tall bottle of the Barts Block Seal (I think that's the way to spell it). Said it's a permanent fix for HG problems and heater cores. I'm afraid of something like that.

    ----------

    I also wish this forum had an Iphone App.

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