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MG Midget and Sprite Technical - Overheating 1500

Over the past few weeks I have been experiencing overheating issues which had not previously been a problem.

I have made the following two changes, over winter I have replaced the inlet manifold as the water pipe that passes through had corroded and had been bypassed by PO. There was also no heater valve inside engine so was always blowing hot air out which was not much fun in hot weather! I have fitted a heater valve and all the missing pipes and all appear to be working correctly.

I have also fitted an oil cooler which has been a great help at improving the oil pressure when hot, I have attached a photo of where I have attached the cooler, there is approximately a gap of between 4" to 6" gap behind the oil cooler and the front of the radiator. This seemed the obvious spot but is it restricting the flow of air through the rad?

The temperature is fine and drops back to normal whilst driving at 30 mph but on a motorway at 60 to 70mph it shoots up quickly, not much fun driving back from Silverstone on Sunday in the hot temperature after a great day out.

I have my thoughts on the cooler, but it would be great to hear of anyone's ideas as its easy to miss what to many may be the obvious.

Thanks
Tim


Tim Lynam

When I added an oil cooler to my frogeye with a crossflow rad I fixed it to the angled panel below the radiator and cut a hole in it for the exit air so it wouldn't effect the air going to the water radiator, I believe the 1500 is the same.
David Billington

I don’t know the recommended position for a cooler on the 1500, but the 1500 doesn’t have the same grill aperture as the earlier models, only the two slots in the front valance. If you’ve fitted your cooler there, you could be seriously restricting the flow to the rad.
Dave O'Neill 2

It doesn't sound like a big problem necessarily to me. With the temperate of the air at the moment the gauge will rise at 60-70 mph. How high does it go, have you heard hissing from the rad cap, seen steam(?). What is your normal gauge reading? Were you driving the car in the hot weather before the last two weeks?

It might just be running warm because its warm, if it doesn't go in the H zone don't worry too much.

Better engine oil with regular, thorough changes helps with engine oil cooling and engine performance (cooler fitted or not).

Oil coolers weren't a factory item with the 1500 and they were exported to hotter climates with just a higher capacity fan (and viscous fan and larger rad for US).

The oil cooler needs an oil stat otherwise during the more usual, even summer, weather here the oil will be often over cooled.

Something I've found in this hot weather is if I close the fresh air flap to the heater box despite the heater supposedly being off the temp gauge rises.

If your car's getting too near the H zone then slow down, have the heater on with the fresh air flap fully open.

You want to keep the fresh air flap fully open at all times anyway even in bitter winter to get the most heater air in to the cabin.
Nigel Atkins

Another thought, have you put a rally plate on the front or moved the number plate, some use stick on number plate to leave the area entirely clear for airflow.
Nigel Atkins

Tim, i am more familiar with the 1275 than the 1500, but that said there will be owners on here of your model than can help you. So you are in the right place !

I would be so bold as to say that if all is good working order than your car is fitted with all the right things to keep itself at the right temp (water wise) if something is on its way out, however the current hot weather will certainly highlight any problems.

Changing hoses, flushing things through, particularly the radiator and heater matrix might be a starting point for you, and these items are easy to get at and change of required.

As for oil, i have a cooler on my car, albeit warmly modified engine, but couldnt say for sure if thats an essential item or not. As you have one leave it there, but others may have more experience on the matter than I.
P Bentley

Thanks David, sounds a good idea cutting a hole at bottom of radiator cowl, was interested to hear if everyone pointed to the oil cooler being the probable culprit.

Nigel, yes there was steam coming from the cap at the worst moment when the gauge did the reach H mark on the temp gauge, yes the weather was hot but not as hot as last year travelling around France at a similar very hot period prior to the fitting of the cooler without any overheating issues.

The oil had been recently changed and all the hoses had been renewed over winter and new coolant used.

If anyone’s got any pics or other tips of siting an oil cooler on a 1500 it would be good to hear as looks like my siting in the obvious spot for ease may be the cause of the overheating.

Tim

Tim Lynam

Tim,
your oil cooler setup is the same as mine and i am not experiencing any over heating issues even in this hot spell. So i do not think your installation is the cause.
You say that you changed all the hoses over the winter, are you sure that you have got all the air out of the system ? I work on the principle that it takes around 4 warm up and cooling down cycles for the water level to become stable and also pay close attention to getting the air out of the top heater hose. I added a bleed device to assist this. I removed the top heater hose from the external pipe and swung it through 90 degrees, added the bleed device and an extra length of heater hose round the heater air intake and back to the external pipe. No pictures to hand, sorry.
I recently fitted silicone hoses and gave the cooling system a thorough flushing out and i discovered that the internal pipe inside the expansion tank had corroded though about half way down, I don't think this caused me any problem but potentially could cause some strange problems.

HTH
Alan
A Pritchett

Thanks Alan, that’s a great help, I believe I have all the air out of the system, but with all the added pipes around the heater box that were added over winter to add the heater tap, there could be a pocket of trapped air somewhere.

I’ve not come across a bleed device before, could be worth investigating further.

I had no problems on a couple of previous longish trips in normal weather, but the recent warm for UK 25 Deg C+ has been too much for the 1500.

Tim
Tim Lynam

Tim,
it's now sounding more serious. Have you checked your pressure cap just in case, it's the correct pressure, in good condition and fully working.

Did you follow the refill instructions in the good book and remove and raise (IIRC? the expansion tank?) hose to expel the air and avoid hot spots.

As you know I'm a big believer in flushing and back-flushing the engine block at coolant change.

Other causes of getting hot can be, er, I'm thinking, er, engine timing, partially blocked exhaust, coolant system(s) of course, dragging brakes, that's all I can think of for those.

I might be wrong but the fact that it cools at 30mph might suggest something on the running of the car rather than or in addition to any coolant issues.

I don't think it'd matter but have you checked you have the heater pipes right way round - and anything else changed recently (filled with some cheap dodgy petrol (95 octane)).
Nigel Atkins

Nigel, I’m sure I have not drained and refilled totally in line with the good book but when I have had air locks before after coolant changes it’s been noticeable and removed by running with the filler cap above the thermostat removed and never had this issue before.

As a total novice to these vehicles as against others, as far as I see it the car uses the fan at lower speeds mainly on its own to cool the engine but at higher speed relies on the flow of air through the rad which my oil cooler is impeding, the trouble I have is I have made two changes to the car which could either be at fault.
The car cools perfectly at low speeds at high temperature but boils up at constant high speed in hot weather which to me points to poor air flow, but I would be more than happy to be proved wrong by someone pointing out to an obvious mistake.
Tim Lynam

The rad is always needed, the fan helps at lower speeds as you say.

One of my points was that you can normally get air out easily without an additional bleed valve but same as relays if you want or need them then that's the thing to do.

Alan has put he has the oil cooler in the same place as you without problems so that would suggest it might not be the oil cooler position in itself.

What about things you can try easily like flushing and back flushing the rad to check no crud has taken up residence there. Or bypassing your heater again (and at the same time taking the opportunity to back-flush and flush the heater matrix).

Where are your horns located?

Have you ever drained, cleaned, flushed or back-flushed out the engine block?

Either your engine (and/or bay) is getting too hot for some reason or your cooling system(s) isn't working as well as it should or the engine's got some additional load or a combination/permutation of all.
Nigel Atkins

Nigel, A good flush is planned for the weekend, but you have picked up on a good point, flushing the engine block. All other areas have been flushed over the past few years but I’ve never found the drain tap on the block, can someone please confirm if there is one on an early 1500 engine?
Tim Lynam

There should be a drain plug on the right side of the engine towards the back, partly obscured by the exhaust manifold IIRC. Another way to drain the block is to pull the water pump out, which gives you a chance to give it a coat of looking at.
Greybeard

Tim,
just got to say it - the Driver's Handbook tells you about the engine block drain.

If you want my simple but thorough method(s) of cleaning the cooling/heating system just email me, first and last name at bt internet dot com.
Nigel Atkins

Hopefully I have found the drain plug as per Greybeard's explanation and per the good old Drivers Handbook although the picture is a little deceiving, but I shall see if it's the correct plug tomorrow.

Any information would be greatly appreciated on your draining process, I still look back on your list of oils/bulbs etc sent several years ago, may all be obvious but any new knowledge is much appreciated, will drop you an email.

Tim Lynam

Speed flush added to the rad, ran the car for 10 mins up to normal temp, found and removed engine drain plug with engine off expecting a gush of hot water and nothing!

Either no water in engine block or blocked drain hole, hopefully the latter.

After giving the drain hole a good clean out the top of the hole allows a pice of wire into the hole for 8mm the bottom of hole only 4mm.

As I have no idea what’s behind the hole I don’t want to use too much force and do any internal damage, anyone had a similar issue or knows how deep the drain hole is?
Tim Lynam

You're not going to damage anything by having a good root with a bit of fence wire or something, but it might not be the drain that's blocked. Could be the water jacket gallery itself bunged up slowly over the years until it finally starts overheating. Either way you need to get water flowing again.
Good luck.
Greybeard

Just a thought from previous experience - have you checked the ignition advance at high rpms?

It might also be worth pulling one of the plugs out after a bout of overheating and checking whether you have a lean mixture.

Either will cause the engine to overheat.
Chris at Octarine Services

Tim - you have mail.
Nigel Atkins

After much prodding and cursing the drain plug was unblocked, drained and thoroughly flushed and back flushed and refilled.

Time will tell if this has done the trick.

Thanks for all the tips they are all much appreciated and plenty more to work on if the overheating continues.
Tim Lynam

Hi Tim, my 1500 overheated when I started using as a day car. Particularly in traffic. In the end I took the cooling and heating systems out, cleaned all hoses and pipes, back flushed both radiators, removed header tank and flushed, and prised drain in block to reverse flush. I did this twice with a flush fluid and a good run in between.
I now have a ‘cool’ 1500 that needs a high temp stat in the winter to warm up and heat the tootsies.
Right now the stat is out. Gets up to about half way on the gauge in traffic otherwise around a quarter on the gauge and a little higher at 60 to 70.
If you are not sure if your system is clear, empty it and measure the coolant you can pour in from scratch. I was amazed at how little I could get in before the clean out, and how accurate the good book was after I cleaned it.
My sump was another revelation when I changed the oil for the first time. Not enough oil went in. After removing the sump I found the crap in the sump when removed allowed me to put the correct amount of oil in.
All helps with the cooling.
The good book points the way :-)

Hope this helps, Dave
Dave Squire

Well done Tim. I once had a 6 cylinder Triumph so badly blocked I had to pull the head and put caustic soda in the block galleries. Nasty stuff. If you're getting water flowing well from the drain I think you'll have got away with it.
Just a thought - what coolant are you using? I'm a recent convert to pink (OAT) antifreeze which is a long-life solution. Some modern engines demand it, but even old iron engines like ours benefit from the better corrosion protection.
CATERPILLAR specify it for the 3412s in my Lifeboat and I send samples twice a year for analysis. I've never had to change it yet.
Greybeard

Well done, you'll soon know if you have improvements. If the day's aren't hot enough to fully match your 70mph Silverstone run then perhaps on a hot day try simulating it by taking a run up a long steep hill at a steady speed so the engine has to work hard at lower speed/revs/torque.

I'm with Dave, enjoy the car now, but if you've only really concentrated on the engine block then later you'd be better to do the whole system including rad and matrix.

Dave also makes a good point that I'd forgotten about, look at the dry fill capacity and how much you can get in on refill and that tells you residue not drained off so potential for weakening refill solution and potential for muck, crud and bits in the rest of the water and oil systems.

If you change coolant types you really need to drain and siphon out all of the previous type and thorough flushes (reverse flushes) as there have been photos of glup bunging up systems from IIRC mixing coolants types plus you don't the old lot diluting the effect of the fresh lot.
Nigel Atkins

Tim,
You are using new coolant. Water transports much more heath per gallon than coolant. I once had the same symptoms in warm weather, half coolant half water solved the problem.
I use to clean the cooling system with one dishwashing tablet for one hour while driving. Than reverse rinse with water and replace with the 50/50 % mix.
Flip Brühl

I added just over 3 litres of diluted Blue coolant, approx 1 litre of coolant to 2 litres of water, if I'm correct the system takes just over 4 litres to fill, so after flushing out with clean water there could have been around 1 litre of water left undrained in the system.

Looks like the system needs strengthening up a bit after reading the previous comments but as the cars not been for a run yet it will probably require topping up after a few miles and time will tell if the problem is sorted.


Tim Lynam

It shouldn't need topping up again if you followed the instructions in the Driver's Handbook which will also tell you the dry fill capacity in the 'General Data' section.

If, the 1 litre of residue is just flush water then your coolant/antifreeze mixture would be 25%, 1l coolant to 3l water (if residue was just water) a bit thin for if the car is used in coldest part of winter or it sits outside year round.
Nigel Atkins

This thread was discussed between 24/07/2018 and 31/07/2018

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