Losing water… but why?

[PyramidCoral]

Afternoon all,

Just as a disclaimer, I’m running an FB with original everything under the bonnet and I have a query about my radiator and what’s going on. Note that I’ve had my radiator serviced and flushed only recently and it’s got a new 7lb cap.

I went for a 50km drive where 95% was cruising at 100kmh give or take. I pulled into a carpark and noticed a muddy drip for the last 5m and a sizeable puddle directly under the radiator — all of which came out of the rubber overflow tube.

I decided to close the bonnet and carry on shopping, and worry about it upon return when the engine was cooler.

I threw in no more than half a litre of spring water that I had on me which got to about a couple of mm over the fins.

Because I had a few things to do, I kept driving and parking — checking if any drips showed up on the panel below the tube and if anything, it wasn’t more than half a teaspoon.

At my last stop, I visited a friend and he insisted I put a bit more water in and that wound up being a litre and I’d say that sat about 20mm over the fins. I checked the dipstick and there was no trace of coolant / water too.

After that, I got stuck in crazy night traffic — Brisbane can throw up unusual things on weekends — and eventually I wound up on the freeway home with 30km of constant 100kmh driving.

I pop the bonnet as soon as I got home and visually, it didn’t lose a drop of water. Not even so much as a dry stain below the tube.

I just popped the radiator cap open and the level looks exactly the same as when my mate topped it up.

What I’d like to know is, what happened when it decided to spit out so much coolant?

Apologies if this seems like a silly query but I’m relatively new to the eccentricities of grey motor Holdens, but I’m keen to learn as much as I enjoy driving them.

Thanks

Donnie

[Blacky]

Welcome to the forum Donnie , I have a theory .......

My ute used to puke out a litre or more of water every day driving home from the nationals, to the point where it would start to overheat later in the day, one year we had a lay day in Esperance so I went to the local Natrad and told them what was going on with it. He sold me a 14lb cap and explained that the only reason these old girls had a 7lb cap in back in the day was because the radiators and hoses weren't what they are today so the cap was the weak point to avoid damage to anything else. My radiator had been recored years earlier so I threw the cap on and it hasn't used any water ever since.

[EK283]

Blacky's theory is spot on.

The only issue with large psi caps can be the heater core, especially if it is old. Most are rated at 7psi only.
If you are real keen put in a recovery cap and a bottle at the end of the overflow hose, this will catch the blowby but suck it back in when it cools.
You can then measure the usage and eliminate things like a failing head gasket.

Greg

[ardiesse]

Donnie,

Early Holden cooling systems don't like it when you go from freeway speeds to a dead stop immediately. There's a lot of heat stored in the cylinder head, and when you turn the engine off, the coolant stops flowing also. The stored heat's got to go somewhere, the coolant inside the head heats up to boiling, and you push water out the overflow tube.

Mud and sludge in the cooling system can make the radiator cap seal poorly.

At a guess, I'd say your radiator is only just up to the job. A heavy-duty three-row radiator core will help a lot.

Rob

[Harv]

I find with the FB that it does not like a full radiator. It will puke until it is about 5mm above the core, then stays steady at that level.

Cheers,
Harv

[PyramidCoral]

I appreciate the insights, guys and the warm welcome too.

All I want to do is drive it and enjoy it without thinking of what might potentially go ka-boom!

I should add that when I am sitting in the 100kmh range, I do back off the pedal from time to time and do the bulk of my slowing down using the motor first before applying the brakes when approaching off-ramps.