Morris Minor Owners Club

bmcecosse wrote:Ahh but you want the water circulation from the back of the head ALL the time - especially in hot weather!

So how did they overcome that one on the Metro, or are you saying the "rear" of the block wouldn't get so hot on a transverse- its still the furthest point!

I know the Metro uses a different by-pass system, but I would strongly recommend leaving the standard by-pass hose in place, and leave the heater circuit open all the time.

The only overheating problem I have had was when I removed the head-to-pump bypass and drilled a couple of holes in the thermostat. Put it back to standard and no problems at all since.

I am intrigued that the Metro did remove the outlet from the back of the head, as I have heard, but never seen any comparisons, that there can be a problem with local overheating on modified engines if it is closed. On the Metro, being transverse, there is some direct air cooling on to what is the back of the engine in an in-line application, but would it make that much difference?

If some of the air coming out of the heater is cold it's worth checking the foam around the matrix.
Also how draughty is the car in general?
If there is cold air coming in round the doors and the gear lever, pedals etc. the heater will always struggle even if its uprated.

How do you plan to build in a fudge factor or adjustment to take care of different fuel pump flows?

The no-bypass seemed to work ok for Metros and later Minis (and Maestro and Ital) - and my 1380 Mini had no bypass, and cooled fine. The heater would start giving heat - not just slightly warm air - within 1/4 mile! Can't see how not having the bypass would cause your overheating Richard - but I'm not doubting your findings!

The overheating wasn't that the engine 'boiled', it was local overheating during the warm-up - the temperature gauge just climbed rapidly until the stat opened, which caused the No.1 exhaust valve to nip on the bronze guide, which caused a misfire, which ultimately burnt out the No.1 exhaust valve! There was a similar problem 'under load' as well.

Replaced the by-pass hose, valve and guides and no problems since. It seems that the reduced water flow at the front of the head caused a series of undesirable events. Maybe on a standard (ish) engine it could be ok, but it was not something that filled me with confidence, so the Metro water pump had to go!!

Roy, can we clear up one thing please? Metros etc. do have a bypass, just not the same as the Minor.

Phew, I'll have to be careful mentioning the bypass system in posts again!

I spent hours calibrating the temperature sender against a proper thermocouple type thermometer and a pan of hot water. I have driven the car quite a bit since my last post, down to Hertfordshire and up to Wolverhampton, and the engine warms up to between 78-82oC at 70mph on a very cold night. I think running around town wasn't giving the engine a proper chance to warm up (I drive fairly sedately until someone cuts me up on the cov ring road!) I am a lot happier now I think the new thermostat has made a difference.

Re: adjustment for different fuel pumps, I could add an adjustable 'click per litre' setting that can be changed for different fuel pumps - though assuming the diaphragms are all the same they shouldn't vary too much.

I think there is something to be said for not having too much information available, after I add mpg and mph to the readout I'll have to put a week aside for worrying about speedo calibration and why my I am only getting XX mpg rather than 37 or whatever.

Back off topic again: I think the main beef with the bypass system is the little hose that has a nasty habit of cracking leaving you stranded. I guess that is the reason Rover redesigned it.

Aye - but Rover never fitted that hose - they always provided a proper hose! The aftermarket wrinkled hose is a disaster waiting to happen!

The aftermarket wrinkled hose is a disaster waiting to happen!

Agreed just use a small piece of heater hose and it will last for years.

Hi Grahmo!
Just seen this thread so am a bit late.
1. Like you, my (checked) temp guage often shows the water temp to be well below the thermo opening temp. I've assumed that the engine block itself is a great big radiator and keeps it down at slower speeds. I've a 89C stat fitted and am thinking of going to a 91C. (My 1098 trav is standard.)
2. I've found that the normal temp measurement position below the stat is not always the best place to measure the max water temp. I've got rid of the cylinderhead-to-block hose and found the highest temps are in the supply to the heater - which is always open. I've had no overheating without the wretched bypass.
3. I've been using a petrol pump stroke counter for years, and highly recommend it. It drives thro' a bit of 1960s electronics an electromechancal counter which I can set to zero by a button and switch out of the circuit, so I have to do runs at a set speed for a set time, usually a half or full minute on a bit of flat motorway and get a "fuel gone" figure. The pump is calibrated by counting strokes into a glass winchester jar (like you use for wine making) that I've previously marked on the outside after filling it from a commercial petrol pump - and noting how much I've bought! Then you do a bit of simple maths with the calibration and "fuel gone" figures and produce lots of lovely wobbly graphs.
What would help in this simple system would be a cut off for the counter after a set time. Pounding along at 70+ watching both your watch and the counter gets stressfull. Regards, MikeN.

I suggest that changing an 89 degree stat for a 91 stat will not make any noticeable difference ! When you eliminated the bypass hose - did you drill any holes in the stat ? If so - that's where the heat ius leaking away. For winter use - NO holes !!

Don't expect any differnce in temp reading Bmc - just to raise overall temp when hot. Didn't do any drillings in the stat and am (successfully) relying on flow through the heater till the stat opens. Got rid of the bypass cos I do runs to Newcastle of 600 miles round trip (often with a trailer) and don't want a burst esp on the motorways. MikeN.

Absolutely ! Bypass hose must have caused more lost time/heartache/money than any other aspect of the A series engine. If you do all these miles - I'm sure you would benefit by removing the mechanical fan - and fitting an electric fan for that once-a-year time you get stuck in a jam.

A driver in removing the by-pass hose was that when I changed the head to non-leaded I found that the 40 year old spigots on the block and old head had got wafer thin - so trouble was waiting to occur. I cut them off and tapped the holes 3/8 inch Whitworth (I think) and plugged them with gunged bolts. Re fan replacement, I've been sketching out an idea to allow an ordinary fan driven by a flat pulley that might moved on a pivoted frame to engage with the back of the fan belt - like is used to engage the drive on my ancient garden cultivator and on some lathes. More moggy-ish!
Sorry to pervert the course of your thread Gimho! I'm glad we've an electronic wizz aboard.
(Now I wonder if I could interest you in electronic measurement of the SU carb piston lift? I've got this rig running with a carb, vacuum cleaner and BS 848 air intake to calibrate the piston lift for airflow. If I could do this on the road while counting the pump strokes I could get fuel/air ratios while moving! Corrr! But perhaps this should be another thread!) Regards, MikeN.