Heater Mystery??

[rolythevan]

I have owned for 10 years a 1969 Austin Minor van that I started towing a Classic fold down caravan with for the first time last year
I encounter overheating during towing (perticularly during slow traffic) last year , so I have fitted a new Radiator- New water pump & finally an additional manually switched Kenlow fan (In front of the radiator) & finally fitted a Temprature gauge

this seemed to control the overheating at the end of last summer

My Mystery is !! ---- I used it for the first time towing last week-end (About a 4 hour drive on the motorway) and the Heater kept getting warm for about 30 mins& then blowing Stone cold again for about 30 mins then warming up again repeating the cycle over & over

The van went in for a service just before the week-end trip
it is not losing water,
the cooling system is pressurised
the heater matrix was flushed & (de-airlocked!) no bockages or much silt
the temprature gauge reads a constant 82' during the run
the kenlow fan was off

although this is not effecting the running of the van , I would like to know why this is happening, So I can relax and enjoy the drive !!

Over to the best Technical brains in the MMOC !

Regards

John Kelly

[Peetee]

It might be worth checking the heater valve. I have seen them so choked that only a fraction of the flow is possible. Also the intermittant problem might be down to a sizable rust flake from the head or block turning around.

Over to the best Technical brains in the MMOC !

Oh, sorry. I didn't see that bit. It seems I might have spoken out of turn.

[rolythevan]

Thanks
I will check that out this week-end
That is one item in the coolant system i've not looked at

I'll report if I find anything

Cheers

[leyther8008]

Seem odd, but could it be conected to the thermostat opening and closing? seems a bit slow in cycling time for it to be that but something is regulating the flow and I can only suggest that, would be interested to know the answer when you find it?

[bmcecosse]

There should have been no need for all that expense! Simply fitting a double fan (ie two blades at right angles) will cool anything - or in extremis (hot country only) - the multi blade fan from a Spridget is even better. Sounds like a good reverse flush with a garden hose is called for - through the block and the heater - and check there are no kinks in the heater hose runs. If the engine is only doing low revs it won't move enough water into the heater to keep it hot all the time - if the problem continues experiment with running in 3rd gear for a bit and see if it's ok then. Final tip of course is to remove (or block) the waterpump bypass hose which helps heater output greatly - although mostly to do with speed of warming up rather than steady running which should be unaffected.

[Mogwai]

do the hoses on the heater matrix go in on the bottom & out at the top as this helps to purge air out the system

[rolythevan]

The mystery has been solved ,

Thanks PeeTee, it was your sugestion that I take off the heater valve
apart from being gummed up it had a piece of rubber debris partaly blocking the hole (looked a bit like 2/3rds of a rubber "O" ring ??!!
anyway after clearing this out went for a trial run & wow the heater efficency is up by 100% and it didn't go through the hot & cold cycle

I wonder how long this has been partally blocked ?, I just thought It was normal for the heater to be next to useless

Of course the new mystery is Where did the rubber debris come from?

But thanks to all for your sugestions

Regards

John kelly

[Kevin]

I wonder how long this has been partally blocked ?,

They tend to do that over a period of time and unless there is a problem they never get looked at.

[Peetee]

The mystery has been solved ,

Thanks PeeTee,

Wow I got something right!

[Matt]

now you just need to get an MoT to match ;)

[Peetee]

That's waiting for the next pay day.