Celebrating the products of AEC Southall Ltd, most famous as builder of London's buses.

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 Post subject: A219 thermostats
PostPosted: Sat Nov 25, 2017 10:38 am 

Joined: Fri Apr 14, 2017 9:01 am
Posts: 6
Some technical help wanted here, regarding the overheating on my BEA coach MLL738. The engine came from a provincial Regal IV and has an oil filter fitted, no problem. It also has a "conventional" wax type thermostat fitted. that has seized up and with that removed the engine runs at 70c. I replaced it with a "standard" LT wax thermostat as fitted to RTs, RMs etc and that causes the engine to run at 98c. Comparing the 2, the original stat has a much wider aperture than the LT type, say 2 1/4" diameter compared to the RM type at 1 3/4" diameter. So the extra internal diameter would allow a better water flow better suited to longer distance coach operation. Maybe this is why so many RFs have overheating problems these days? According to my AEC Regal IV parts catalogue the thermostat is part no. 81-1545. Maybe the larger thermostat was fitted in the larger 11.3 engine or those fitted in BR railcars?

 Post subject: Re: A219 thermostats
PostPosted: Sat Nov 25, 2017 7:03 pm 

Joined: Tue Oct 11, 2016 9:44 pm
Posts: 15
RFs don't have overheating problems these days or in the past. Unless the radiator is blocked, of course.

The main reason they appear to boil is that they are over-filled with water. It is only expansion that chucks water out and drops the level to the correct point. Of course in LT days, drivers just filled them up again until the water spilled down the front. And then the whole thing happened again down the road, and they cursed them (unfairly) for overheating. When cold, the water level should literally only be just visible in the header tank.

We have three RFs - the first did originally boil on long shallow hills (but not elsewhere) and when the radiator was stripped down there were only three tubes that weren't blocked! After fitting a reconditioned radiator that one has never boiled since, and the other two never have. And we are talking of a period of over thirty years!

I don't see any reason why an LT thermostat should give you any problems. Many RFs ran without a thermostat at all in post-LT use, although that isn't an option I would choose.


 Post subject: Re: A219 thermostats
PostPosted: Sun Dec 03, 2017 10:11 pm 

Joined: Sat Jan 14, 2012 10:24 pm
Posts: 109
An engine which has poor compression will run hot if it is subjected to full load for a sustained period. One of the common reasons for overhauling AEC engines was because of a lack of power caused by low compression. Add on a radiator in poor internal condition from years of running with either plain water or a weak antifreeze mixture and overheating is a predictable consequence. Underfloor engine buses and particularly some AEC models also suffered from a lack of adequate airflow through the radiator noticeable at higher speeds. So given a tired engine stuggling with its load trying to maintain higher road speeds and hindered by a partially blocked radiator it is not surprising that it should run hot. Should the coolant level in the header tank drop significantly below the level of the saloon heaters then air locks in the system are likely to develop leading to initially localised overheating.

I will check later this week, but IIRC the RF thermostat housing requires a bellows type thermostat capable of blocking off the by pass port. If this port is not covered at operating temperature then the coolant flow will take the path of least resistance; which is not via the radiator.

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