3800 cooling system from HELL

[Matthew Jeschke]

I'm to the point where I am ready to put in some sort of stop leak in my cooling system. A friend recommended silver solder but I don't thing they make that anymore?

Anybody have a good stop leak they recommend for a cooling system.

Backstory: I got this 2006 Buick Lucerne nearly 10 years ago with 90k miles on it. It's been a great vehicle aside from junk accumulators on the 4T65E transmission and cooling issues. The cooling system has always leaked as well as the transmission clunking (my theory is the accumulators are cracked). I digress about transmission back to the cooling system. I've since put:

New metal bypass tubes (why bypass tubes??? why??)
New radiator (nearly impossible to swap)
New water pump

Using contrast dye I've checked:

Intake manifold GOOD
No leaks on front of motor (bank1?)
Cannot see easily back of motor (bank2?) but appears find so far as I can see.

However, always a puddle forms under bank 2 at rear of block (near driver side tire).

I can see some spray near the harmonic balancer on the sub fame but nothing on the pullies??

I can see a bit of contrast on under the ignition coil however, there's no puddle there under the vehicle.

I don't think the heads are leaking or the intake. It's not the water pump, or bypass tubes. The heater core and supply lines are not leaking either. The radiator and hoses are good.

My mind is blown. I cannot figure out where this leak is coming from.

Vehicle is great aside from the bleeping tranny clunk due to cheap plastic accumulators and this cooling system I'm constantly chasing leaks in. Long story short, unless somebody knows this system well and were I might fix it... I'm going to dump stop leak in it and hope for the best. Super annoyed great motor otherwise, great power, but perpetually leaky cooling system. It's like GM took this car 99% of the way to great and said well lets just create a leaky cooling system and clunky transmission so we can save 15 cents building it.

 

[bigdog9191999]

If you don't get any other responses I am quite familiar with 3800 stuff.

However I do want to clarify bypass tubes. Is this in reference to coolant elbows?

 

[89Suburban]

This is always my go to. I keep a couple in the tool chest for emergencies.

Alumaseal Radiator Stop Leak 0.75oz

Shop for Alumaseal Radiator Stop Leak 0.75oz with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

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@OR VietVet @Tonyrodz are you familiar with this engine and this issue?

 

[Tonyrodz]

This is always my go to. I keep a couple in the tool chest for emergencies.

Alumaseal Radiator Stop Leak 0.75oz

Shop for Alumaseal Radiator Stop Leak 0.75oz with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com

@OR VietVet @Tonyrodz are you familiar with this engine and this issue?

Sorry not familiar with the newer 3800s, only the older late 80's to mid 90s. I'm sure they're not the same.

 

[bigdog9191999]

Same basic setup from 97+. L36 And should be basically identical from 04+ when they switched to the L26 till end of life.


When I get a min I can list out all the places cooling system makes a seal at. This may help visualize where the leak could be. That is if it isn't something like the lower intake gasket. Which can be quite common on a 3800.

 

[bill1013]

Barr’s Pelletized Stop Leak always worked for me. You might consider looking into using it.

 

[Tonyrodz]

Barr’s Pelletized Stop Leak always worked for me. You might consider looking into using it.

Great stuff. Plugged a big hole in the radiator in my 89 Formula.

 

[Matthew Jeschke]

Thanks for the tips! I knew I'd come to the right place. Everybody on here always seems to know their stuff!!! Really appreciate it.

If you don't get any other responses I am quite familiar with 3800 stuff.

However I do want to clarify bypass tubes. Is this in reference to coolant elbows?

Correct I replaced the coolant elbows, twice *sigh*. First time with OEM plastic ones, second time I learned of aftermarket metal ones. The later have held nicely. I also learned that GM spec coolant dissolves the o-rings on those. So I'm using Preston (not GM spec / universal coolant).

This is always my go to. I keep a couple in the tool chest for emergencies.

Alumaseal Radiator Stop Leak 0.75oz

Shop for Alumaseal Radiator Stop Leak 0.75oz with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com

@OR VietVet @Tonyrodz are you familiar with this engine and this issue?

Great to know I'll snag this.

Barr’s Pelletized Stop Leak always worked for me. You might consider looking into using it.

Maybe I'll try this first?

Sorry not familiar with the newer 3800s, only the older late 80's to mid 90s. I'm sure they're not the same.

No clue. It's a GREAT motor otherwise. Efficient and good power. I've had several 3100's and this 3800. My friends also had coolant problems with their 3800's of this vintage. I drove the newer 3500? it's TERRIBLE no power. I'd love to sort this out but making me increasingly frustrated lol

The 4T65E is a great transmission too. However, they obviously went through and cheapened it, in addition to introducing weak points so it eventually prematurely fails much like 4L60E.

Same basic setup from 97+. L36 And should be basically identical from 04+ when they switched to the L26 till end of life.


When I get a min I can list out all the places cooling system makes a seal at. This may help visualize where the leak could be. That is if it isn't something like the lower intake gasket. Which can be quite common on a 3800.

That would be AWESOME if you have an easy way to do that. It maybe I missed a seal I didn't realize. I'd MUCH prefer to fix root issue as apposed to stop leak it.

 

[bigdog9191999]

I will start at the coolant inlet on the driver's side in the intake where the thermostat is. And just follow the cooling system around and mention all the places I know there is a gasket or such ( there are more than one thinks. )

The gasket around the stat itself seals the stat and housing.

Lim these should be metal by this year but does not mean they could not fail. The rubber around the coolant ports can still degrade.

Upper intake to tb gasket

Gasket between upper and lower intake. Should be thinking plastic with rubber around the sealing surfaces. ( There are passages from the lim to the tub, thus sealing points in-between everything)



There is a port with a "cap" under the Tb in the lower intake that has a gasket ( very rarely any issue here)

From there it all flows through the heads/block through passages to the passenger side on this side you have.

Front cover to block ( OEM is a coated metal gasket. )

Pump on the front cover.

Elbows. One from lim and one from front cover to/through alt bracket.


Front cover / hose to radiator. Rad to engine and rad to overflow.

 

[B-train]

I chased a mystery leak on my daughter's 2008 Lucerne 3.8L. Did a Google search after racking my brain and found 1 thread that mentions a coolant cover on the back of the motor........blocked by the bell housing of the transmission. The article read similar to your post and that is what they eventually found to be the problem. I'd look for some pictures of the Series III 3.8L and see if you can correlate it.

I put in some K-Stop stop leak and its been fine ever since. That stuff works magic. I won't pull a trans to fix a coolant leak on a $1500 car.

@Matthew Jeschke