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Coolant system blockage?

Blanking Out

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Hi, I'm trying hard to work out why it is that I can only get 2 litres of water/coolant back into my 1979 Spitfire cooling system (it should be 4.5 litres, I think). I drained the old coolant, then flushed out as many pipes as I could get at, checked thermostat etc, but still the radiator is overflowing by the time I've only got 2 litres in.

I also unscrewed the engine block drain plug but nothing came out, The 'hole' doesn't really seem to lead anywhere, though - just up to what seems like solid metal (maybe the side of a cylinder block?), but there is a small amount of dry, black residue that I've scraped out of there.

I gave it a go with some chemical flush and started the engine, but after only a few minutes it sounded like a noisy crackling, fizzing noise from inside, as if overheating badly, so I abandoned that.

I might as well also add that there are fairly bad, smelly exhaust fumes, but that might be a separate issue? The aspect of only getting 2 litres in is baffling me.

Any ideas would be great.


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It sounds like your block is full of crud. The drain plug should fairly gush out on a clean engine but your experience of it seeming to be a dead end is sadly very common. You need to have a really, really good poke at it with a bent screwdriver. You can't damage the block - it's cast iron - but you need to be fairly vigorous to shift the agglomerated rust and casting sand residue (yes, there nearly always is casting sand residue in the waterways - the factory weren't very good at cleaning).

Did you run it with the radiator cap off? You've probably got an airlock on re-filling and that's what caused the "overheating noises". Idling with the cap off and gradually filling as the coolant recedes can sometimes shift that. Also, make sure the heater is full on.

Do persist with the flushing agent, too. If your block is full of crud there's good odds the radiator and hoses are, too. And the pipe through the manifold. And the return pipe down below.

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You probably don't want to hear this,  but you may need to remove the frost plugs and to poke round in behind them  to remove all the rubbish... I had to do this with my 2500 block. Mind you it was easier for me as I had the motor out.


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Thanks to both of you there!

The frost plugs - are those the circular things on the side of the block that are supposed to pop out if the coolant freezes, or have I got that totally wrong?

Getting inside sounds like it might be necessary, but so far the thought of that seemed beyond me - but maybe not, though (I'm quite a novice). I might try directing a hose into that drain plug area.

I blew down several pipes and a certain amount of muddy-looking fluid flew out, but maybe there is more, so I'll try again with the flush.

The heater doesn't work, but the lever on the dash is permanently in the hot position (heater valve is jammed). There are a lot of bits to put right! When I did drive it it seemed to drive pretty well, though, apart from starting to overheat (oh, and the bad fumes).



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Quoted from Blanking Out-

The frost plugs - are those the circular things on the side of the block that are supposed to pop out if the coolant freezes

Yes, those are the ones. If the car is fairly new to you and has always had cooling issues in that time, then there's a fairly good chance some of the frost plugs (also called "core plugs") are on the verge of rusting through and held together only by the large deposits of crud behind them. It'll be worth removing and replacing them, even if it does involve a rather large amount of dismantling. As Tony says, it's a lot easier with the engine on a stand rather than in the car, but it's perfectly possible just with the manifolds removed, with one exception. There's a plug on the front of the block behind the engine front plate. You may need to just hope that one's good.

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