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Foaming Bedford


mike30841

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Has anyone come across this problem? My Bedford OX produces white foam in the coolant, and this overflows from the neck of the radiator when working hard. There are a couple of slight cracks in the filler neck, but as the system doesn't appear to be pressurised, I can't see that this should be a problem. The system contains anti-freeze as a corrosion inhibitor - I have tried boiling a sample of the coolant in a pan, but cannot replicate the foaming.

 

I have now flushed the system with a proprietory cleaner (loads of crap came out of the block!) , and whilst I haven't had it out on a run yet, there was no foaming when filled with plain water, or when I put in a weaker mixture of anti-freeze, so I am vaguely hopeful that I have at least improved things. I have a nagging feeling though, that the problem could be down to a leaking head gasket. I did a compression test today, with the following result:-

 

Number 1: 110psi

Number 2: 120 psi

Number 3: 120 psi

Number 4: 140psi

Number 5: 110 psi

Number 6: 110 psi

 

Nothing particularly conclusive there, although it looks to me as though things are getting pretty worn. Does anyone know what the cylinder pressures should be, and does anyone have any thoughts as to the cause of the foaming? Incidentally, there is no significant drop in the coolant level, even on runs of 40 or 50 miles, and there is no sign of oil in the water or vice versa.

 

Any help would be appreciated.

 

Mike.

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have you any signs of water contamination in sump eg oil going greyer paler ?. Reason i ask is if very slight head gasket problem it will some times if vehicle is stood for long periods between use manifest its self as above symptoms after a run why i dont know although it dont seem to give problems on overheating side of things

Edited by cosrec
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I've had a similar problem with my 43 MW, she needed a new water pump and during the fitting of this I found she had no thermostat, but I've not had her on a run since. She usually "foams at the nose" after a short burst of power after she's hot, but post fitting the new thermostat she seems to run (in the garage!) a lot better. I too did the compressions and got a consistent 140 psi on each pot, and there's no oil in water or water in oil! someone said to me that i could have overfilled her with water, but after a run when she's foamed the water level is below the fin tops on the rad and I'm not sure that that is correct! I'll give her a run friday and see what happens, and let you know. I may fit a water temp gauge and have it hidden somewhere, though I would like to keep her original, I don't want to toast a good engine by thinking she's just blowing a bit of excess water when she's got a real overheating problem!

 

I'll be back

 

mike

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Many thanks for your replies, chaps. You have certainly thrown up some interesting possibilities. I will post a picture of the filler neck on the OX tomorrow when I have a bit of time, but from the picture of the MW I suspect the innards are missing from mine - there is neither a pipe inside or anything for the cap to seat against, it looks as though there should be some sort of fitment screwed in to the neck. Another point raised is the fact that foaming occurs when there is no thermostat fitted, again this is missing on the OX.

 

Watch this space....

 

Mike.

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IMG_8171a.JPG

 

As promised, I attach a picture of the filler neck on the OX. Am I correct in thinking that there should be a fitment screwed in to the neck which the filler cap seats against? If there is a part missing, could this be causing the foaming?

 

Look forward to hearing your thoughts...

 

Mike.

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If it is the same setup as the MW radiator then you appear to be missing the large castellated 'nut' that has the rubber seal under it. Nor do you seem to have the spring loaded 'tube with a flared top' that bears on it. So yes, you wont be getting a seal and the foaming is just the liquid spilling out at inappropriate times. A diagram of the correct setup is to be found in at least one of the repro manuals available. Surprisingly when I asked a pal to check in his vintage 'bible' tonight the diagram is not there. The depth setting of the nut is quite important, the absence of the nut and spring loaded bit even more so :-) I would get these missing bits sorted out before spending any further time on possible blown head gaskets etc, I think you have found the cause.

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Mine too hasn't got the dip tube, which according to the manual is there to "stop the anti-freeze being diluted" by overfilling, but the radiator cap does not seal down against the castellated ring, the dip tube is held up against it with a spring with a rubber seal on the underside of the castellated ring. I'm in the process of making a dip tube for mine, and will get hold of some piano wire and wind a spring for it, as I doubt there's many of these things around. John Morter didn't have one when I picked up my water pump. I don't see that it makes much difference really- the radiator cap valve will see the same pressure anyway- if mine still foams, then I will suspect that the cap diaphragm valve is passing (or the springs weak- like someone else on the chat suspects) I haven't seen a radiator cap anywhere that looks any better than mine! heres a scan of the manual. Do you have one?bedford filler cap.jpg

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Hi everyone,

 

Thanks for your input on this one - it certainly looks as though the missing relief valve is the cause of the problem. As luck would have it, I have a spare amongst my QL bits which I can use, but the spring is long gone - has anyone out there got a spare they would be prepared to part with? I have e-mailed Mike Humphreys separately to see if he is getting some made.

 

Mike.

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That's interesting - if it makes no difference whether the dip tube/relief valve is fitted, then we are back to the question of what is causing the foaming. I did give it a good run on Saturday, still without the dip tube etc, and whilst it is better ( no foam coming out of the radiator neck), there was still white foam in the header tank. I am beginning to wonder if perhaps there is localised boiling due to scaling of the water jacket - there was an awful lot of scale came out when I flushed the system, and I think it likely that as much again still remains. I am planning to give it another good flushing before I start replacing the thermostat and relief valve - I think I have managed to modify a suitable spring, and Mike Humpreys is looking into getting a few new ones manufactured.

 

I have discussed the problem with Norman Aish and he is of the opinion that it is more likely to be a cylinder head gasket issue - apparently the civilian version is not fitted with the relief valve, The manual for the civilian version quotes a head bolt torque of 78 -83 lb/ft, increased by 10 lb/ft when anti freeze is added to the coolant, so maybe it is something to do with the composition of the head gasket?

 

In the meantime, have stripped down the front brakes to check everything over. I seem to have caught them just in time as both cylinders were beginning to weep, and the bores are shot. In comparing the old wheel cylinders with a new spare, I discovered why the brakes were so keen - I thought the old cylinders looked a bit big, and indeed they were, as at some time in the past someone had fitted QL cylinders!! ( OX cylinder bore is 1 5/16", QL is ! 1/2"). Needless to say I will be fitting the correct size when it goes back together.

 

Mike.

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  • 4 weeks later...

Well, I've eventually got my MW ready for the Poppy LIne next week, having cleaned out the engine and radiator using some Holts 2 stage heavy duty rad flush stuff- and removing and rebuilding the rear engine drain cock, then fitting a new thermostat she doesn't foam at the nose any more.....but why was she doing it in the first place? I'm not sure.

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