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RE: Our 2000 Seville STS 4.6 Northstar

We have a coolant leak out of the head gasket just behind the water pump-

Has anyone attempted to use a stopleak added to the coolant to cure the problem -If so, how long has it lasted/would you recommend that approach?? Thanks for your input-

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RE: Our 2000 Seville STS 4.6 Northstar

We have a coolant leak out of the head gasket just behind the water pump-

Has anyone attempted to use a stopleak added to the coolant to cure the problem -If so, how long has it lasted/would you recommend that approach?? Thanks for your input-

The title of your thread states cyliner head gasket coolant leak....

What makes you think its the head gasket?

The Northstar head gasket rarely leaks externally, so your leak is suspect. If you are standing looking over the driver side fender, the water pump is installed in a crossover that attaches to both heads in FOUR places with seals. THOSE seals go bad and you will get a coolant leak at those FOUR locations, it will run down the side of the block, and can run down the crossover to drip off of it.

In addition the water pump body has an ORING behind it that if its bad can leak at THAT location.

My car leaked from the crossover gaskets and the water pump body. It is difficult to replace the crossover gaskets, about $700 in a garage. Its ALL labor. I had a difficult time stopping the leak behind my water pump.

DO NOT USE SEALANT/SEALER

Use the GM specified COOLING SYSTEM SUPPLEMENT, it will stop small leaks.

Explain the leak more for us

Welcome aboard

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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Since it is a 2000, I would suspect the crossover manifold. I believe it is a somewhat common 2000+ leak point. Like BBF said, not likely a head gasket.

Thanks guys for your fast reply!

In order to locate the coolant leak I jacked up the front of the car and removed the large

plastic front bottom panel and also all of the air induction parts and front upper cross plastic

panel. Even at that it is somewhat difficult to see the interface of the cylinder head and the block.

The leak is at the interface of the head and block at the lower front corner and drips down from

there. Over night it will leave a puddle @ 2 to 3 sq. inches.

My first approach was to introduce some aluma-seal ( a fine granulated aluminum product I have

used in the past on other vehicles) into the upper or lower radiator hose.

I bought the Helms manuels when we bought the car as I have always done my own work.

I'm not looking forward to removing the head.

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My first approach was to introduce some aluma-seal ( a fine granulated aluminum product I have

used in the past on other vehicles) into the upper or lower radiator hose.

DO NOT use that stuff. If you use anything, use the Barleaks tabs (G12BP) or get them from the dealer.

Are you sure it is not coming from the water pump "O" ring seal? Use a mirror and a flashlight to see if there is any leakage from the shaft seal. I REALLY doubt it is the head gasket.

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FIX THE PROBLEM!

Have you determined what the problem is yet? I gave you a bunch of info above to help you determine what it is...

Use ONLY the GM Cooling Supplement

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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FIX THE PROBLEM!

Have you determined what the problem is yet? I gave you a bunch of info above to help you determine what it is...

Use ONLY the GM Cooling Supplement

I have not had time to pursue the coolant leak problem any further. My next step is to try to

check out the cross over plumbing etc. to be sure that is not the source of the leak early next

week.

I have attempted to look behing the water pump where the belt drive pully resides and that area

appears to be dry.

In the meantime I am going to check with the dealer to locate the G.M. supplement tabs and auto

supply stores for the bars leak tabs.

Thanks again for the help!

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  • 4 weeks later...
RE: Our 2000 Seville STS 4.6 Northstar

We have a coolant leak out of the head gasket just behind the water pump-

Has anyone attempted to use a stopleak added to the coolant to cure the problem -If so, how long has it lasted/would you recommend that approach?? Thanks for your input-

The leak is likely not from the head gasket but from what is known as the water pump housing or crossover. It uses four different gaskets to seal at different points to the back of each head and the block. It is not uncommon for these gaskets to fail. Engineering has redesigned them more than once since 2000 and I have replaced tons over the last 10 years.

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That was my first post and I now realize that I was being redundant. It looks like these guys have your problem figured out already.

Cool welcome aboard, introduce yourself, what do you do for a living?

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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  • 4 weeks later...
That was my first post and I now realize that I was being redundant. It looks like these guys have your problem figured out already.

Cool welcome aboard, introduce yourself, what do you do for a living?

I am sorry for the delay on reporting back on the head gasket leak issue on the 2000 northstar engine at

71000 miles.

I replaced the water pump cover gasket, changed the Dex Cool and added 3 GM cooling system seal tabs

to cooling system. The engine now has another 1000 miles on it with no visible coolant leaks or weeping

from the head gasket. I also replaced the temp sensor to the left of the steering column behind the small

grill that has the small fan that was making the noise when cold. I used Cadillac parts.

Thanks again for all of your input.

I am a retired mechanical eng. and have had a life long auto hobby.

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I am sorry for the delay on reporting back on the head gasket leak issue on the 2000 northstar engine at

71000 miles.

I replaced the water pump cover gasket, changed the Dex Cool and added 3 GM cooling system seal tabs

to cooling system. The engine now has another 1000 miles on it with no visible coolant leaks or weeping

from the head gasket. I also replaced the temp sensor to the left of the steering column behind the small

grill that has the small fan that was making the noise when cold. I used Cadillac parts.

Thanks again for all of your input.

I am a retired mechanical eng. and have had a life long auto hobby.

Welcome.

Very glad to hear that you got it all sorted out and fixed.

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  • 2 weeks later...
That was my first post and I now realize that I was being redundant. It looks like these guys have your problem figured out already.

Cool welcome aboard, introduce yourself, what do you do for a living?

I am sorry for the delay on reporting back on the head gasket leak issue on the 2000 northstar engine at

71000 miles.

I replaced the water pump cover gasket, changed the Dex Cool and added 3 GM cooling system seal tabs

to cooling system. The engine now has another 1000 miles on it with no visible coolant leaks or weeping

from the head gasket. I also replaced the temp sensor to the left of the steering column behind the small

grill that has the small fan that was making the noise when cold. I used Cadillac parts.

Thanks again for all of your input.

I am a retired mechanical eng. and have had a life long auto hobby.

Is that temp sensor on the back of the head near the firewall under the EGR valve?

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That was my first post and I now realize that I was being redundant. It looks like these guys have your problem figured out already.

Cool welcome aboard, introduce yourself, what do you do for a living?

I am sorry for the delay on reporting back on the head gasket leak issue on the 2000 northstar engine at

71000 miles.

I replaced the water pump cover gasket, changed the Dex Cool and added 3 GM cooling system seal tabs

to cooling system. The engine now has another 1000 miles on it with no visible coolant leaks or weeping

from the head gasket. I also replaced the temp sensor to the left of the steering column behind the small

grill that has the small fan that was making the noise when cold. I used Cadillac parts.

Thanks again for all of your input.

I am a retired mechanical eng. and have had a life long auto hobby.

Is that temp sensor on the back of the head near the firewall under the EGR valve?

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That was my first post and I now realize that I was being redundant. It looks like these guys have your problem figured out already.

Cool welcome aboard, introduce yourself, what do you do for a living?

I am sorry for the delay on reporting back on the head gasket leak issue on the 2000 northstar engine at

71000 miles.

I replaced the water pump cover gasket, changed the Dex Cool and added 3 GM cooling system seal tabs

to cooling system. The engine now has another 1000 miles on it with no visible coolant leaks or weeping

from the head gasket. I also replaced the temp sensor to the left of the steering column behind the small

grill that has the small fan that was making the noise when cold. I used Cadillac parts.

Thanks again for all of your input.

I am a retired mechanical eng. and have had a life long auto hobby.

Glad to heard it. Yes that interior temp sensor fan can get noisy like laptop and computer fans, the grease dries out and they get noisy...

With these engines, there are a lot of places that they can leak coolant, now you see, never assume the worst...

Stick around, we can help you anytime, Mike

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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I also replaced the temp sensor to the left of the steering column behind the small

grill that has the small fan that was making the noise when cold. I used Cadillac parts.

Thanks again for all of your input.

I am a retired mechanical eng. and have had a life long auto hobby.

Is that temp sensor on the back of the head near the firewall under the EGR valve?

I think he was talking about the IN CAR TEMP sensor.

The one behind the little grill in the dash that tells the HVAC unit the temperature inside the car.

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That was my first post and I now realize that I was being redundant. It looks like these guys have your problem figured out already.

Cool welcome aboard, introduce yourself, what do you do for a living?

I am sorry for the delay on reporting back on the head gasket leak issue on the 2000 northstar engine at

71000 miles.

I replaced the water pump cover gasket, changed the Dex Cool and added 3 GM cooling system seal tabs

to cooling system. The engine now has another 1000 miles on it with no visible coolant leaks or weeping

from the head gasket. I also replaced the temp sensor to the left of the steering column behind the small

grill that has the small fan that was making the noise when cold. I used Cadillac parts.

Thanks again for all of your input.

I am a retired mechanical eng. and have had a life long auto hobby.

How do u replace that sensor in the car left of the steering column behind the lil grill. Itz hard to get to...

Live Fast Drive Luxuriously

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Probably the easiest thing on the car to replace. It's attached to the hood latch bracket. Right out in the open. Won't even need any bandaids.

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Probably the easiest thing on the car to replace. It's attached to the hood latch bracket. Right out in the open. Won't even need any bandaids.

Sorry to be mr simpleton but wat actually comes of to gain acess to the sensor and motir fan??

Live Fast Drive Luxuriously

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Oops. When I read "grill" I thought you where talking about the ambient air temp sensor. Sorry. Cabin temp sensor is another story and a little more difficult. Open the drivers door. See that access panel on the end of the dash. I think it is accessible through there.

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