Overheating Seville

[elindsay]

One thing that I dont get about the overheating is that it will go up and down while driving it may go up one to two bars and while im watching it can come right back down. Any ideas?

[BodybyFisher]

One thing that I dont get about the overheating is that it will go up and down while driving it may go up one to two bars and while im watching it can come right back down. Any ideas?

What are you doing when this occurs?, what speed, traffic? etc

How long does this action take?, I could see it rising in traffic and dropping quickly when you begin to travel at highway speeds, but it sounds like you are seeing spikes while you are travelling at a constant speed?

Have you changed the thermostat?, I don't want to go back and read this thread from the beginning, so forgive me if you answered this question

[elindsay]

Hi looks like misery likes company I'm having the exact same problem with my 1999 Cadillac STS

I've added a new water pump, thermostat, radiator belt and holes and I still can't stop it from overheating.

Will run for about 30 minutes to 40 minutes before overheating even at idle.

I also did the chemical test like you did and came up negative and I have nothing coming out of the tailpipe .

so you're not in this boat alone I'm trying to find an answer but also running short on money after all the work I've done .

would like to save the car so if you find an answer sending a message and and if I find one I'll send you a message.

good luck to both of us .

Just used Thermagasket it cost $250 and you have to call them and let them know it is a northstar engine. The chemical they send is only $99 but you need this other piece. I do not know if it will last but I just drove 25 miles on the interstate at 70 -80 miles and the temp gauge did not move. And this was up and down hills. I live in a valley and either way on interstate is uphill. I love it, I will let you know in a couple of weeks if still working.

[Cadillac Jim]

None of the headgasket-in-a-bottle products work on any car. Don't even *think* about trying them on your Northstar, particularly if the coolant passes a test for combustion by-products, or your cooling system passes a pressure test.

If the car overheats and the coolant passes the combustion byproducts test, you don't have a blown head gasket and thus have a conventional overheating checklist. The only things peculiar to the Northstar are the water pump belt and tensioner, which are on the rear (driver's side) of the engine and are driven by a pulley connected to one of the cams on the left (front) bank of cylinders.

The cooling checklist is simple:

• Make sure that the coolant is at least 50% antifreeze, and not more than 70% antifreeze.
  
• Make sure that the cooling system holds pressure and that the coolant level is OK.
  
• Make sure that the thermostat bypass is flowing. This hose connects to the surge tank near the top front, where it is easily seen. With a cold engine, disconnect it at the surge tank by loosening the hose clamp, start the engine, and see if there is a steady flow of coolant out of the hose.
  
• Check the radiator for leaves or other obstruction. Also, make sure that the radiator itself isn't clogged.
  
• Make sure that the fans are OK. The simplest check is to turn on the A/C and see if both fans are on HIGH.
  

The dealer checklist in the 1997 FSM, pages 6-178 and 6-179 (with instructions on repair procedures on succeeding pages) basically goes through this, and the repair procedures to fix anything wrong that is found.

The most common problems are loss of coolant due to leaks (radiator cap, hoses, clamps, radiator-usually a cracked tank, heater core, etc.), clogged thermostat bypass, or bad fan/fan fuse/fan relay. The first thing that people think of, the thermostat, is found as the problem less often than a clogged thermostat bypass or a leaking radiator cap on the surge tank, or not enough anti-freeze in the coolant.

Two things to watch out for are the right radiator cap for a pressurized surge tank (not the old style where the overflow line goes to an unpressurized overflow tank) and a thermostat that has been put in backwards, is the wrong type, or both. The radiator cap should be a 15 psi unit and the thermostat should be a 180 F unit.

Intermittent overheating problems, particularly in the summer, may be due to a clogged heater core along with a partly clogged thermostat bypass.

[sts03]

I thought the radiator cap was supposed to be 18 psi, atleast mine is for my 03 sts .my old cap and the new one I got from napa are both 18 psi.

[BodybyFisher]

Hi looks like misery likes company I'm having the exact same problem with my 1999 Cadillac STS

I've added a new water pump, thermostat, radiator belt and holes and I still can't stop it from overheating.

Will run for about 30 minutes to 40 minutes before overheating even at idle.

I also did the chemical test like you did and came up negative and I have nothing coming out of the tailpipe .

so you're not in this boat alone I'm trying to find an answer but also running short on money after all the work I've done .

would like to save the car so if you find an answer sending a message and and if I find one I'll send you a message.

good luck to both of us .

Just used Thermagasket it cost $250 and you have to call them and let them know it is a northstar engine. The chemical they send is only $99 but you need this other piece. I do not know if it will last but I just drove 25 miles on the interstate at 70 -80 miles and the temp gauge did not move. And this was up and down hills. I live in a valley and either way on interstate is uphill. I love it, I will let you know in a couple of weeks if still working.

Did you test for combustion by products before proceded to use this sealer? Was a pressure test performed to find leaks? You talked about leaks around the cap, is the tank cracked. Was the cap replaced.? As Jim noted, did you do NORMAL diagnosis BEFORE you dosed it with sealer? Unless it it leaking the radiator and water pump are NEVER the cause of overheating. If you did a pressure test, leaks would show up.

We are here to help. You SHOULD have asked before you wasted $250 if this "FIX" works. It will NOT work. This is not a breeched headgasket ala a piece is missing and this glass sealer will seal it, assuming your bolts pulled, you are getting an up and down movement that will not be sealed by ANY sealer, the movement permits coolant to enter the combustion chamber past the head gasket and visa versa combustion gases and heat will enter the coolant. There is a member here who will come in and disagree with me, but that is my reasoning for why the sealant will never work permenantly on this engine. Sealants fix physical breeches NOT movement induced breeches

You may improve the problem temporarily but unless the engine is repaired you will not have a reliable car to go on long trips or to get stuck in traffic with.

Don't get excited

[Cadillac Jim]

I thought the radiator cap was supposed to be 18 psi, atleast mine is for my 03 sts .my old cap and the new one I got from napa are both 18 psi.

The Rock Auto site lists three radiator caps for the 2000 Seville: Gates, Stant, and AC/Delco. The Gates 31405 and Stant 10239/11239 are rated "15 psi (SAE range 14-18 psi)" and the AC/Delco RC87 is rated at 18 psi.

It looks like there may be some change in the way that specs are given out these days; it seems possible that what I used to call a 15 psi radiator cap is now rated by the maximum allowable pressure for the part, 18 psi.

The bottom line is to get the one listed for your car by make, model and year from the catalog of a reputable manufactuer like Gates, Stant, or AC/Delco.

[elindsay]

I know it will be a temp. fix but the car has 158000 miles and to repair the head gasket $3500 to $4000 with no garantee. So I gave it a shot. I have drove over 100 miles so far without overheating. I love the car but will take the $4000 and put it down on a new car

[Cadillac Jim]

The problem I have is that, apparently, you have not verified that it is a head gasket problem. I bought a car for half-price once because it was burning oil and all it needed was a PCV valve, an oil change and a tune-up; I drove it trouble-free with no oil consumption for years. I very strongly suggest that you get the coolant checked for combustion by-products before you make any other decisions.

[BodybyFisher]

Thanks Jim, that is exactly the point, but it looks like he is going to sell it, and he just stuck a bandaid on it

[Cadillac Jim]

If the sodium silicate slug stops the overheating, he may - or may not - have verified that the problem is a head gasket. My problem is that if it isn't a head gasket, and he just topped off the coolant or stopped leaks in the hoses or radiator or increased the coolant boiling point, and the sodium silicate may also gel to silica at the hot spots in the heads, insulating them from the coolant flow and making them hotter spots in the combustion chambers. I don't even know if boiling out the heads would cure that.

[elindsay]

I know the mechanic had tried everything he knew and told me head gaskets or go trade the car. Not ready to trade, need to save up some more money for that.

[Cadillac Jim]

Did the mechanic tell you *why* he thought that the head gaskets were bad? If he did a coolant test or it failed a pressure test with no exernal leaks in the cooling system, then he is on solid ground. If there is a head gasket problem, his advice is sound, of course. Politely ask him why he thinks there is a head gasket problem; it sounds like he did do a pressure test or some such.

[ialicea]

Hi I did this and it worked out for me to keep my car from overheatting.

I got a kit form steel seal

I put up a video on my work see if this may help you out.

[KHE]

I know the mechanic had tried everything he knew and told me head gaskets or go trade the car. Not ready to trade, need to save up some more money for that.

Nice... I hope you disclose your "fix" to the prospective buyer.