Drain the cooling system 3.8 engine

[Desmo]

Hello,

although I replaced the three gaskets between the intake manifold and the cylinder head, small leaks have developed. The contact surfaces were smooth and undamaged. I would like to replace the gaskets.

How can I drain the newly filled cooling system enough to remove the intake manifold and thermostat housing without any coolant leaking out? I'd rather not disconnect the lower radiator hoses for fear of losing the fresh coolant. Thanky for your advice.

Regards
John

[mgcjag]

Open the drain tap in the block and use a bucket to collect the coolant....use sealant on both sides of gaskets

[Desmo]

Thank you Steve. I will do my best.

Regards
John

[paydase]

Your issue will be to evaluate how much of the coolant you want to drain using the tap in the block before removing the headers without coolant spilling around.
Maybe a couple of liters?...

[abowie]

There's been debate about this in the past, but I always use silicone sealant around the water ways on the inlet manifold.

As to draining the coolant, either use the tap or just disconnect the lower radiator hose.

IMO the tap doesn't drop the coolant cleanly; it tends to splash all over the lower edge of the block.

[bitsobrits]

Does the 3.8 not have a petcock in the bottom of the radiator? I've had two 3.8's, but it's been a long time ago. My current 4.2 has a petcock on the bottom right of the rad and is very convenient for partial draining of the system.

[Gfhug]

When draining via the block tap I use a small funnel and short piece of garden hose to direct the flow into a bowl for collection.

Geoff

[paydase]

Same for me.
Here using clean demineralised water to flush all the remaining acidic glycol:

IMG_20250226_161709.jpg (249.52 KiB) Viewed 11685 times

[mtnjag]

As Steve says don't you have a petcock in the radiator?

It should. My orig Marsten has one and two subsequent radiators both have a drain petcock.

Easier than the block drain. I only use that to get the last bit out on a coolant change. You don't need to do that to get it below the level of the intake.

[Desmo]

Hello,

thank you. Because they are still the original drain petcocks, I do not dare unscrew them. Maybe I will carefully unscrew the petcock on the left end of the radiator.... .

Regards
John

[mtnjag]

My orig Marsten Alum had a little faucet style like in the block.
Not the unscrew type. Sounds like your orig was replaced.