diagnosing a blocked radiator??

[jamesheath]

I've been doing a light re-commissioning of an Austin Seven (I've known the owner for a while, but I've recently taken it over) and got to the point this week of driving it round the block.
It cut out the first time round, but after I put some more petrol in it went round twice nicely, before starting to steam... (it was -3 deg C ambient).

The radiator isn't the best, and the fan is spaced a little far away possibly.
Also, there's a little oil in the water (though no water in the oil) so I suspect I'll need to take the head off and look at that (one of the head studs sheared off years ago). 

I ran it up again stationary at a lively tickover, and it took 6 minutes for the rad water to go from 5 deg C to 80 deg C in the rad header tank.
the bottom of the rad was pretty much cold.

I've taken the hoses off and back flushed the rad and the engine expecting to get a tonne of crud out, but got nothing (Indeed the coolant in there was really very clean).

I happen to have a thermal camera that connects to my phone - using that the engine seems to be warming fairly evenly (I was expecting no. 4 to heat up quicker/get hotter):
   

The rad seems is stripy and WAY hotter in the header tank than anywhere else. Can it be blocked such that water won't circulate through it by thermo-syphon, yet flows freely when a hose is attached? 
   

I realise that the thermosyphon will be creating a very low pressure difference...

Does anyone have any good diagnosis tests? Or do I have enough evidence already?

Thanks,

James

[Rick F]

I had a very similar problem with my RP - although I didn't have the high-tec equipment you are employing. I used a Mk 1 hand to feel the radiator and discoverd large areas significantly colder than the rest.

This followed a severe boiling after an over-winter lay up with a drained radiator and about a five-mile test run.

After an abortive attempt with rdaiator flushing products, I bit the bullet and had it re-cored.

[jamesheath]

Thanks Rick - so has anyone had success flushing stubborn crud out of a radiator with chemicals?
I read a long post about the chemicals used, but I don't think anyone described how bad their rad was to start, and whether it actually improved.... (fernox or Holts seemed to come out on top).
It's been backflushed (in position) with a hose, and the resulting effluent was pretty much clean (I really was expecting a brown sludge!)

[Mike Costigan]

From that thermal image of the radiator, it looks to me like the left-hand side two-thirds of the bottom tank is completely blocked. Flushing through is just going to clear the right hand side (which looks clear anyway), as the intake is on that side of the system (so heat is the only means of creating significant flow on the left-hand side). If the core looks externally to be in good condition it might be worth removing the bottom tank, otherwise it looks like a new radiator.

[Charles P]

Thanks Rick - so has anyone had success flushing stubborn crud out of a radiator with chemicals?
I read a long post about the chemicals used, but I don't think anyone described how bad their rad was to start, and whether it actually improved.... (fernox or Holts seemed to come out on top).
It's been backflushed (in position) with a hose, and the resulting effluent was pretty much clean (I really was expecting a brown sludge!)

Yes.
Depending upon the nature of the crud I've had success with Fernox DS40 or DS3. DS3 is basically industrial sized kettle descaler and DS40 an expensive acid based clean.
The other good option is warm, 50% diluted brick/patio cleaning acid. You need to be careful, of course, but bung up the bottom pipe, try it for a short time (5 mins) and tip the waste into a clean bucket for examination. Some crud will be hopefully be dissolved and some loosened.
You've got an unusable radiator. What's the worst that can happen?

c

[Steve Jones]

I cleaned out the radiator on my P Type Lea Francis using 50% Brick Cleaner (Hydrochloric Acid) back in 2005. These radiators have a unique shape and a wet shell and are therefore rather more expensive to re-core than those on Sevens to say the least!! It was heart in mouth time and I bottled out after leaving the stuff in for 15 minutes. The amount of crud that came out was unbelievable and I remember looking through the filler neck and seeing bright, shiny copper that looked as if it was brand new. The down side, of course, is that it also removes bits of crud that had been blocking slight leaks in the core but that was something that was sortable to the extent we took the car down to a very hot Angouleme in France later in the year with minimal bother.

I'd go for it. What have you got to lose?

Steve

[John H]

If the radiator is gummed up, what about the block? Is it worth removing the side water manifold on the block, to check that it isn't full of crud behind there?

[Hedd_Jones]

Thanks Rick - so has anyone had success flushing stubborn crud out of a radiator with chemicals?
I read a long post about the chemicals used, but I don't think anyone described how bad their rad was to start, and whether it actually improved.... (fernox or Holts seemed to come out on top).
It's been backflushed (in position) with a hose, and the resulting effluent was pretty much clean (I really was expecting a brown sludge!)

Yes.
Depending upon the nature of the crud I've had success with Fernox DS40 or DS3. DS3 is basically industrial sized kettle descaler and DS40 an expensive acid based clean.
The other good option is warm, 50% diluted brick/patio cleaning acid. You need to be careful, of course, but bung up the bottom pipe, try it for a short time (5 mins) and tip the waste into a clean bucket for examination. Some crud will be hopefully be dissolved and some loosened.
You've got an unusable radiator. What's the worst that can happen?

c

Yup

Kill or cure. Viakal also works. It all depends where the blockage is, and the general condition of everything else.

The chemicals will dissolve the blockage in time, but they may also dissolve corrosion products that might be sealing your rad from leakage.

We tried neat brick acid on my Mates Aveling barford dumper (with Ford 8 engine). Made the rad into a colander. Oops. Nevertheless it was U/S as it was. It had scored the bores it had got that hot

[JonE]

Hedd, would the dilute brick acid just be taking away barsleak type and egg white substances, or do you think it will be taking away some structural radiator?! i.e. could one re-implement the bunger-uppers afterward and hope it might re-seal?

[Charles P]

Living in a very hard water area I've found that a few decent hot runs with plain tap water after a flush can help to seal any weeps.
After that it's drain and refill with dehumidifier water and add acorrosion inhibitor.