23 replies to this topic

[maph2]

hi,

i am running a rover 1992 1275 carb engine in my 72 mini. the gearbox, head, dizzy is standard rover apart from a stage one kit (mg inlet, kn pancake, hif44, lcb, single box rc40) and 1/5:1 rocker gear. the water pump is a brand new deep cast impeller type and the rad is a mini spares 2 core with the standard fan removed and a electric fan in it place. the themostat in the block and the fan switch in the rad are new. block/rad have been flushed and refilled accordingly.

the problem is that around town it is fine, the gauge shows just under half. it will sit in traffic on a hot day all day without overheating but as soon as i go on the motorway and cruise a 70 mph , the needle creeps up to over 3/4 (switch on heater time!).

considering it is supposed to be a 2 core rad that is suitable for turbos etc, i am puzzled why it overheats.

could be that minispares did not give me a 2 core , but a standard one or something else. would a lean mixture, timing etc cause this? i will be fitting an oil cooler for motorway use .i'll see what that does.

any help would be great

matt

[Pavel]

Too much timing advance and/or lean mixtures will cause the car to over heat.

As you say its only when you're cruising on the motorway at 70, i.e. doing quite high revs. Perhaps your needle or timing advance aren't correct, giving either too much timing advance or lean mixture at higher RPMs, which may cause what you are experiencing...

Did you have your needle changed when installing the stage one kit?

Also is your vacuum advance connected from the dizzy to the carb? (i think that's how its meant to go...)

[bluebottle]

try refitting the fan to the water pump, this helps guide the air through the rad when the car is moving

[Bluemini]

If you dont have the fan on all the time, it will get too hot, I'm supprised it doesn't overheat more often and at lower speeds! If you had a front mounted rad then you could probly get away with having a thermastaticly switch fan, but not on a side rad.

[Pavel]

Actually if you read around you'll see its something quite a number of people do, completely replace the pump fan with an electric one... Seems to get teh job done accodring to other people!

But I would try refitting the fan back as already said, since all it will do is provide extra cooling and that can't be a bad thing!

[fireman-sam]

have you got the elec fanscking the air or blowing it?

[maph2]

the elec fan is definitely set up correctly - it blow through from the engine bay to the wheel arch (have checked fa performance by reversing fan and swapping polarity on motor to find most powerful setting).

the needle was put in at HiTech (Dudley) when it was rolling roaded.

from what you guys have said, i think is a weak mixture. if i remember, the vacuum advance was blocked up (pipe had a piece of carb needle shoved in it) when the car was rolling roaded at hitech, but i think it fell out when i overhauled the dizzy and i forgot to put it back. i think i'll put it back and try it.

anybody going to the malvern show on sunday 11th?

matt

[Sfanatic]

I've just covered this on the Pistonheads 'Mini' Forum.
If you have a big (i.e. a 1275 or bigger) engine you cannot cope with just an electric fan. If the engine is modified further it will create even more heat.
Think about this: A 1275 engine has always been right on the limit for cooling anyway. The 11 blade fan struggles to cope in hot weather and that is working in what is known as a 'ducted fan' in that it runs in a shroud. In a rally car you have the standard fan plus a manually operated electric fan. How can an electric fan on its own hope to cope with all the engine heat generated when sometimes even the original plus an electric only just cope.
Your best option is to fit a 6-blade fan such as we fit to rally cars, then wire the electric one, which I assume is on the other side of the rad (if it's not then move it), using a manual switch, rather than a stat switch.
You'll have no further problems.
Of course, an incorrect mixture of timing would make it a bit hotter, but if you've deleted the belt driven fan that's where your problem lies.

[maph2]

sfanatic,

thanks for your input. over the weekend i reinstalled the standard rover plastic fan and put the electric fan on the outside of the rad (blowing through the rad to the mech fan). however, the heating problem was worse, which i think still indicates a possible weak mixture/incorrect needle

the rad is definitely a 2 core -you can tell by looking through the rad filler hole, new high cap water pump, themostat etc.

i took the car on to the motorway after setting it up. it was already up to temp (half way on the gauge) before the motorway and not long after reaching 70-75mph the gauge started to creep up to 3/4's (saturday was a fairly warm day). what was odd was that coming off the motorway and driving steadily back home (30-40mph) the temp gauge remained at 3/4's all the way home.

when only the electric fan was on, the temp soon dropped after decelerating from 70mph (even at standstill immediately off the motorway the temp dropped quickly).

as the mech fan pushes air through the rad, i may reverse the blades on the electric fan so to pull air through the rad.

the coolant system is not leaking but i thought also that the head gasket could be leaking and slightly pressurising the coolant (long shot)- no mayo though)

[dklawson]

What? Maph2 wrote:

"thanks for your input. over the weekend i reinstalled the standard rover plastic fan and put the electric fan on the outside of the rad (blowing through the rad to the mech fan). however, the heating problem was worse, which i think still indicates a possible weak mixture/incorrect needle"

Is your statement above a typo? The air should always be blowing from the engine compartment out through the radiator and into the wheel well (electric OR mechanical fan). If you really have the electric blowing towards the mechanical fan neither one will move any air through the radiator and the cooling will not happen.

Fan blades have curves also. Make sure they are turned the right way around. Looking down on them when standing at the front of the car they should look like ( not ) .

Over heating 1275s are probably more common over here than there. There is a progression usually taken to solve things and the electric fan is a last ditch effort. Most people here use the following steps: change to a 165oF thermostat, followed by a 13 psi radiator cap, then change the coolant to a blend with "Water Wetter" (a fluid to enhance heat transfer... ask at your parts supplier). If all these fail then add a second heater core in the engine compartment as an auxiliary radiator. Very few people here have had much luck with electric fans.

[maph2]

nope, that is not a typo - i need to reverse the blades on the elec fan to pull rather than push.

matt

[dklawson]

Reversing the electric fan blades may not in fact work. Look at the ( and ) in my last post. Both of these will push air through the radiator... but the ( orientation pushes "more" air. Likewise, the fan blades on your electric fan won't push instead of pull by reversing the blade. You have to be careful and pay attention when you buy a fan as to whether it's a pusher or a puller.

You'd think that by reversing the polarity of the motor you could handle this by changing the direction of motor rotation. Sadly, not all DC motors seem to work this way, they won't automatically reverse directions by swapping polarity. Just look at the early Mini starter motors... they turn the same direction whether you've got positive or negative ground.

Try wiring your fan wired both ways to see if you can make it pull air through the radiator. Maybe it will work.

[siggy]

Remove the electric fan and just run the std one (correct way round)

It might be that if the one fan is moving more air than the other they may black each other. That might be a wild stab, but worth trying

Siggy

[Woody]

I made the mistake of wiring my electric fan up the wrong way when i fitted a temp switch into the circuit, the mini ran nice untill the electric fan cut in and then almost instantly overheated , the fan was pushing the hot air back through the rad ! , i noticed straight away that there was no hot air coming out from under the N/S/F wheel , i reversed the polarity at the motor and all was well ( the fan was in a plastic cowling and not in contact with the bodys neg earth)
as long as the dc motor is a permenant magnet type it should reverse when you reverse the polarity , starter motors have electro-magnetic field coils so if you reverse the polarity in them they still spin the same way.

[Dan]

I agree, check your fans.
DK, most of the small (10" and less) aftermarket fans available in Britain are designed to be universal and either pull or push according to how they are assembled and the motor polarity. But obviously if this one ain't designed to work that way then it is important to make sure it is being used correctly.