SOMETIMES, even the most difficult of fix-it solutions with modified street machines are caused by the failure of a single component. As with this guy who owned a 1966 VC Valiant, uprated in the engine department by a mill thieved from a Hemi six-powered CL – 4.3 litres of triple Weber-carburetted grunt. It had been running okay for a while, but in the worst of our summer heat, the mongrel began tea-kettle boiling. After a few short open-road runs, the temp gauge went off scale. And when Chrysler’s big six cooled down, a lift of the radiator cap showed nothing but an empty top tank.
Um. Must be a leak somewhere in the cooling system to lose that much of the Tectyl stuff. So he got the VC back to home base, borrowed a cooling system analyser pump, and cooling system analyser pump, and pressurised to 20psi to see where the essential liquid was going. Mate, there wasn’t a leak anywhere. No blown Welch plugs, no split hoses, no seeps from the alloy radiator core – nothing.
With all that eliminated, he figured the cast-iron cylinder head must be moving when the engine got hot, allowing compression gas to leak through the gasket and blow lots of coolant out through the radiator overflow. “I’ll run a tension wrench over all the head bolts; that should sort out the problem,” he reckoned. Did that, went out on the road again until the temp gauge said enough is enough, and went home totally frustrated.
The bloody head gasket must have let go. He lifted the head off, then borrowed a mate’s car to get this to the machine shop, where they said: “We’ll do a full valve job with a deck surface, supply all your gaskets, and your super-quick VC will never boil again.”
Ha! Of course it boiled again. A couple of intelligent blokes he knocked around with suggested his reasonably new alloy radiator was probably full of shit by now, so he had better get the tubes pressure-blasted by an expert. More money. Got that done, refitted the radiator and it pulled the same old tea -kettle stunt again.
So he threw spanners at the wall and kicked his dog, and his mates said it must be the water pump now. “The seal is worn out and lifting under pressure, so it keeps spewing out coolant until it runs dry, and boils. Buy a new pump, fit that and your problem will be fixed.” New pump – no luck.
Where do we go from here? Give it a cylinder compression test, in case that new gasket has let go in a small way, enough to cause the coolant to pump out again. That’s when this guy came around to my shed to borrow a screw-in compression gauge, and was back an hour later with tears in his eyes. He said it went 160psi all the way through one to four, then on five and six, the gauge wouldn’t lift above 45. This didn’t sound right to me, as his engine had been running real well and there was no trace of oil smoke from holes burnt through pistons, so I asked a few probing questions. Like: “When you did the test, did you fully open the throttles on your triple side-draught carburettors?”
“No. I didn’t know you had to do that.”
“Go back and try again, as closed throttles on multi-carb layouts when you perform a startercranked compression test will often give you a false reading if one is shut tight.”
The bloke went away with my compressiontesting gauge, and still came back looking worried. All six cylinders, now checked again with the Weber throttles fully open this time around, had hovered around the 160 mark, so the engine must be okay.
But his mates got together to analyse the situation, and decided the thin cast-iron wall in one of his cylinders was obviously porous, leaking gas into the water jacket and pressurising the system. He asked me what I thought. I said: “That sounds like bullshit to me, and is that your car out front?”
“Lift the bonnet, then, and I’ll have a bit of a butcher’s hook at what you got.”
So he did that; the engine bay was neat and clean and dominated by the triple 45mm Webers of this now stand-up engine, of this now stand-up engine, but there were obvious signs that coolant had been regularly escaping and blowing out from under the radiator cap. Radiator cap? Looked new, stamped 13psi on the top, but I never trust anything, let alone a small and vital part like this.
It was a bit hard to twist and remove off the aluminium neck welded to the top tank, which wasn’t unusual, but there were no chunks of block rust between the bottom neoprene cap seal and the seating face of the neck, and he said the cap was only a few weeks old – “bought before my mongrel car began boiling”.
I thought: “Oh yes,” and did a quick blow with my mouth on the seal of the cap to check if the inner vacuum valve was seating to hold in the pressure. And it wasn’t – I blew straight through.
“That’s your problem right there. There’s no way this cap is sealing your system. Fit this new one of mine, and go testing out on the road.”
He did just that, and his VC street machine never boiled again! s