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MG Midget and Sprite Technical - Overheating - Fan cowl?

Hi guys,

Am back - and it's time to get the niggles sorted. First up my Sprite gets rather hot when the car is stationary but the engine is running. It's absolutely fine when travelling (guage sits at N or thereabouts). This is a 1971, 1275, standard setup. New thermostat during the engine rebuild and it opens just fine as the rad and hoses all get hot.

So I reckon the problem is that the pump mounted fan isn't pulling air through the rad when the car is stationary. That adds up given that there's quite a big gap (1 to 2" - but I've not measured it) between the fan and the radiator.

Should there be a cowl around the fan blades? I can't find one in the Moss / MGOC catalogues. Failing that, anyone got a photo of a 1275 standard fan and rad showing the clearance between the two? Or anyone care to measure theirs for me?

Ant
Ant Allen

a couple of inches sounds about right and no ... there isn't a cowl.

If the temp just rises a little above normal and stays there I wouldn't worry. if it keeps rising then you'll need to look further as it should be fine.

I've changed to an electric fan - but the old engine fan was just fine at idle. It would sit a little hotter than during normal running but that is entirely normal.
Dean Smith ('73 RWA)

... and of course it all depends on what 'N' means for your gauge ... you might try calibrating it in just-boiled water to see where 212F or 100C should be. Reaching these temps in idle is fine; should be around 85-90 when tooling along around 40-60, according to 'stat fitted.

A
Anthony Cutler

Well mine gets hotter and hotter. The guage gets well up towards the top of the scale before I wuss out and switch it off. And then it goes even higher once the coolant stops flowing.

The guage was new 6 months ago and is the mercury type. The sender end is slightly damaged due to being fitted without the spacer by the PO so it's a bit mashed (now fitted with spacer), but given that it rises to N and sits there nicely when being driven that suggests it's all working ok. Radiator definitely isn't blocked as it's all ok when moving along. Likewise for thermostat. I was hoping that I am simply missing a cowl, but evidently there never was one.

So - What's happening? The fan is turning with the engine, but air isn't being drawn through the radiator. With a 1-2" gap that doesn't surprise me, but if that's normal, what's gone wrong?

Ant
Ant Allen

try a new rad cap
Alex Sturgeon

I don't know if it's possible to fit the fan the wrong way round?
Garyfrog

Not possible to put the fan on backwards. Check not only the functioning of the pressure cap, but make sure it's the correct pressure rating. Too little or too much pressure can cause issues. Make sure you have enough coolant. Remove filler plug on radiator and make sure radiator is full to the top while idling. Recently I was losing a little coolant and didn't notice. When I checked the radiator at idle, coolant was cascading like a waterfall down the right hand side. Also I had a head gasket fail adn vent exhaust into the coolant. This would be pretty obvious since you would lose coolant as the revs are up, but not necessarily at idle. Just some simple things you may have already checked. Good luck.
CJCharvet

Interesting thought on the fan. I have yet to investigate it but I'll take a look.

Rad cap - mine looks quite new but obviously I can't be sure. How would this help? It's not boiling up and pushing coolant out of the overflow.

Ant
Ant Allen

Cross posting. Sorry.

re the rad cap - what pressure should it be?

my engine has just been rebuilt so I doubt I have a head gasket fault, unless due to me overheating it (erm!?!). I have filled the rad as you describe, and run it several times and topped up to the rad to bleed the system. The heater is nice and hot so no air in there.

Ant
Ant Allen

15 psi on later midget and 7 psi on early mk1 & 2s, best way to bleed a cooling system is to run the engine in idle with the cap off (or rad plug in midget) and the air self bleeds out of the system
Alex Sturgeon

Hi Ant.

Firstly it is not possible to fit a midget fan totally the wrong way however it is possible to fit a Mini fan which would then be the wrong way and cause problems.
Check therefore thay you have not had a mini fan fitted

A faulty or wrong pressure cap will not affect the temperature of the engine, all it does is to allow the water to run hotter without boiling. (increased pressure raises the oiling point of water)

Assuming the engine is set up correctly my normal advice for overheating would be to get the radiator sorted by having it re cored. However I am not sure that is your problem because you seem to stay cool when traveling. This would normally be the case when a Mini fan was fitted.

So if it isn't the wrong fan then it would be my advise to re core the radiator. Just for information I have seen new rads block up in probably a little time as 3 to 4 years
Robert (Bob) Midget Turbo

I have a 15psi cap. Surely if the rad was blocked (water side or air side) then it would run too hot when under load too and driving.

How would I ID a mini fan as opposed to a 1971 Sprite fan?

Ant
Ant Allen

Being a self taught expert in this field, here are a couple other areas to check not mentioned so far

is the carb running lean, more air makes a hotter engine. check for air leaks around the ussaual suspects

has the octan rating of the fuel you use changed..."lower"! It has here, and going lower

the antifresse ...No more then 50/50 mix, infact you may want to reduce to 30/70 mix....more anti freeze makes the engine run hotter....think about it, why is it called "Anti-freeze" and not "super-freeze"...try water wetter the less anti, the better it works...good for 10 degrees ferhin.

water pump....how good is it, does it spin really free with out the belt, or is there binding/slaging, are the internal turbin in good shape, or is it rusting away

May try re-torqueing the head gasket....if its loose, then you know the drill

try by-passing the heater maxtrix instead of truning off the heater tap, to help cool the rear cly.

make sure the overflow vent on rad. isnt clogged.

check all your ignition settings, improper adjusted dissy will add temp.


Stat manufacture defect....this is something I Finally learned this last winter, wax stats have changed in the past 3 years, differant chemical formula for the wax, so the wax takes longer to heat up during colder temps, thus the engine over heats BADLY ....this is the case with my truck and is becoming the norm for the age and modle of my truck...it may have worked its way down to our cars. but doulbtful.


The biggest solution I have found in the past 6 months to preventing a hot engine is a 1/8 inch hole in the stat face, not sure what that means for summer driving, but cured my overheating problems at the drop of the hat. during the colder weather

keep us posted...good luck

prop
Prop

oh I also forgot...

Is the fan belt properly adjusted....not to tight on not to lose....should have a 1 - 2 inch of deflection in the center of the longest run between the pulleys

Prop
Prop

Of course I can not argue that logic Ant and if you had simply asked me what could cause the effect you are getting I would have to say, the only way that can occur is if the fan is wrong. But hey there maybe a critical blockage point in the rad where by air rushing through the rad when travelling forward is enough to keep it cool whilst relying on the fan maybe just too much. Very vague I know but just thinking aloud.

OK the Mini fan?

Most Mini fans have multiple arms but looking at the fan and knowing which way it spins you should be able to work out which way the air will be forced. Do you feel confident to make that assessment?
Robert (Bob) Midget Turbo

take a pic of the fan, and post it....someone here will know what it is.

Prop
Prop

Ant

My guess would be radiator. If your engine is fairly standard the radiator has much more capacity than it needs when the car is on the move so it will sit at normal even with the radiator only 50% efficient.
The problem could be either not enough air flow, check for dead flies leaves and general crud, an airline is the best tool to fix.
OR
Not enough coolant flow if you haven't replaced the radiator there could be years of muck in the bottom of it. Try removing the rad turn it upside down and put a hosepipe in the bottom end. Sort of colonic irrigation.

Colin
colin 691

Ant, get your radiator recored, my car has just an electric fan & is ok during normal weather, but it did get hot during summer traffic jams a wing vent sorted that out.
Brad (Sprite IV 1380)

Just to put everyone out of their misery, Ant turned up at the Green Man last night - he has the wrong fan, and it is fitted the wrong way round, so he knows what to do now.
Geoff Mears (1970 Midget)

The wrong fan indeed! Hopefully this is the last of the PO engine build problems I'm going to discover! The engine is (was - now I've sorted it all out) something of a bitser. It is a 12CE but had the early carbs, the wrong rocker and timing cover, had been re-bored but not honed so the rings never bedded in properly, a misaligned rear crank housing with metal gouged from it, and the wrong fan too! Without a direct comparison I wouldn't have noticed the different size and number of blades, but I'm kicking myself for not noticing that the blade angle is wrong and it's pushing air at the rad rather than sucking from it. Obvious now I know. I guess it's from a mini - they're transverse so air enters at the grill and is pushed out through the wing, right?

Anyhow, I believe I've sourced a correct fan so hopefully that puts this one to bed. Phew

Ant
Ant Allen

Well that is good news Ant and a cheap and easy fix (well not too easy but I bet you are happy. Pleased to be of service hope you can find an original fan :-))

Yes the Mini draws air in from the front, passes the engine through the fan and out through the wing. So is a pusher. :-))
Robert (Bob) Midget Turbo

Ant,
If you want an original fan I have one I'll send you for nothing, I removed it when I fitted a Kenlowe.

richard dot amos at gmail dot com

Rich
Rich Amos (1 Sprite 1 Midget!)

(or I'll bring it with me tomorrow to Saturday's race at Oulton Park and you can come watch me sliding around in the wet)
Rich Amos (1 Sprite 1 Midget!)

No, wait, scratch that, I have no idea where it is! I just went to the garage to look for it but it's nowhere to be seen.

...I have a feeling I may have chucked it (quiet at the back!).

As you were....
Rich Amos (1 Sprite 1 Midget!)

Rich,

Thanks for the offer. If you find it let me know. At the moment I'm awaiting a garage search reply from John Collins.

I'm happy to provide a good and loving home to the first one I can get my hands on. :o)

Ant
Ant Allen

This thread was discussed between 06/05/2009 and 08/05/2009

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