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MG MGB Technical - Very hot under bonnet tempreture

Hi, I have a tubular exhaust which has been wrapped to reduce heat transfer. I have also removed the MGB metal fan and replaced with electric thermostat controlled fan. The engine bay is always hot and the electric fan seems to be on constantly. The wonderful weather this weekend has meant the cooling system runs halfway between Normal and Hot. Is this OK or is there someway of allowing more air into the engine bay to help move the hot air out? Appreciate your comments, Pete
Pete Dyble

Hi Peter,
Yes it was very hot on Saturday and my B is set up like yours even down to the tubular exhaust and mine isn't wrapped, I drove my car from North Yorkshire to Appleby in Cumbria and back and noted that my gauge was reading about 180 - 190 F but on the hill climbs went high but not enough to worry about, my car is still on a winter stat 88 C that's because the past two years have been so cold. You could try fitting a summer stat 82 c this should help your engine run cooler.

Regards Patrick
P.T. Tighe

How old is your radiator? Most cooling problems can be traced to clogged, rotten radiators.
Willem van der Veer

Put the engine fan back on and remove the rubber seal round the back of the bonnet.

Nothing wrong with running between N and H - the WHOLE of the black area of the gauge can be considered normal.
Chris at Octarine Services

Half agree with Chris. Wouldn't put the propellor back on, but would remove the centre section of the bonnet seal, a dodge used by many V8 owners. The restricted means of exit for under bonnet air, added to the underside positive pressure creates a slight back pressure in the engine bay which slows through flow through the rad. Removing this section of rubber helps at lower speeds, but the back of the bonnet is a high pressure area (that's why the heater intake is there!). You will want to put the section back in winter any way. The best areas to exit under bonnet air are the wheel arches.............low pressure areas!
Basides the obvious stat, water pump, fan belt, pressure cap, rad issues. Running with a weak mixture, over advanced ignition, under inflated tyres and binding brakes will all contribute to heating woes. If you are using 50/50 coolant reducing the antifreeze to 25/30% makes of a more efficient coolant.
But hell we will be freezing our nadgers off in a couple of weeks!!!
Allan Reeling

An MGB cooling system in good nick can cope with any climatic condition you will find in the UK, including temps of 32 Celcius. Don't fret about the gauge. If the rad isn't boiling over, the car is not overheating. As Willem said, how good is your radiator? How clogged up are the water channels in the block?

I also wouldn't replace the metal fan - these have been known to break due to metal fatigue and they don't half make a mess when a blade comes off. They can come right through the bonnet lid.

Now for under-bonnet heat you can't beat a V8. My gauge (calibrated in degrees F) will go up to 210-220 sitting in traffic on a hot day until the fans pull it down slowly, but the car isn't over-heating. The driver often is, but the car is fine! Don't forget that the pressurised system and the antifreeze both raise the boiling point of water.
Mike Howlett

I like Allan's post and I will definetly be looking at that inner bonnet seal .

Regards Patrick
P.T. Tighe

Peter - our 1800 runs hot with the fan on most of the time at this time of year - our 3.9 with two fans and blockhugger manifolds ran in town when the ambient was 40c - no probs. The rad and fan does need to be working efficently 'though.
Roger W

Hi, many thanks for all your reply's and agree it won't belong before we need addition heat! The radiator is new and system thoroughly cleaned out and flushed, although no antifreeze. Agree with Stat change and antifreeze but not sure of the seal as I have none on mine. Thanks all
Pete Dyble

Peter,
as Mike has pointed out scraping the crud out of the engine drain hole whilst draining and flush isn't often done and needs to be

I'd get coolant/anti-freze in asap as it also contain corrosion inhibitors, I'd drain the existing water out (whilst scrapping the crud out of the engine block) and flush/back-flush/flush-again you'll be surprised how much crud will come out despite you having clean the rad and system recently

I'd also check the pressure cap is the correct type and the seals and spring are fully working, fan belt isn't loose, fan is correct, water pump ok, nothing blocking the passage of air to the rad, the rubber seal above is on the bonnet and I'd add the foam seal above the rad the later cars have to keep cool air flow from getting over the rad

if you want to prepare for winter at the same time you could also include the heater matrix and even remove it to flush/back-flush/flush-again whilst shaking it up and brush the fins clear of debris and replace internal and external seals if require

don't forget to attend to the heater vale and control, lubricate as required, if you want/need to replace the heater valve (my do they get clogged up) then Ashley Hinton possibly make the only non-leaking ones

quick clean the heater fan motor and fan, empty out 'Tom's dick' and you're ready for whatever weather
Nigel Atkins

ETA: forgot to put, wrapped exhausts are considered to transfer/hold heat to the cylinder head
Nigel Atkins

I've just got back from a 3-day 400 miler in Surrey and East Sussex in the roadster and the hottest it got was queueing for the start of the run, including stop-start for half an hour or more on the A22 on the way back between 3pm and 4pm on the Sunday. Bog-standard roadster, needle normally sits about an Ns width below N (since changing the gauge last time) in more temperate times, this got maybe an Ns width above it.

Whilst the gauge may well get up to half-way between N and the start of the H zone before factory fans come on, I'd expect the temp to come down from that once they do, as My V8 does. What is your fan stat set to? What is the actual temperature of your coolant when the temp gauge is reading what you say (be very careful removing the cap as the coolant could be at the indicated temperature hence there is a risk of boiling. If the fan stat is set to the stat temperature which may be too high, and/or the gauge is reading high, then you will get what you say. Is your fan sucking or blowing? Are the blades orientated the correct way? These cars run in desert states without problems, and especially in the UK just shouldn't need after-market electric fans or other modifications.

Engine compartments are going to get hot in this weather, the only exit for hot air is downwards, the tunnel should be easiest but it is mostly filled with bell housing and gearbox so it has to go downwards and under the inner wings, which is contrary to where it wants to go of course. 'Very hot' is very subjective, and as said if it isn't losing coolant it isn't overheating, and anywhere up to the edge of the H zone is 'normal', although by that time you might need to be considering what to do about it.
Paul Hunt

FWIW, 26C ambient, digital thermometer probe through one of the holes in the bulkhead shelf, got up to 50C, temp gauge was about an Ns width above its normal position. Rad inlet was 87C, outlet 75C. And for completeness the upper part of the coil was 67C. All measured with an infra-red thermometer placed right on the object.
Paul Hunt

Hi All, many thanks for all your constructive comments.
Status is as follows. The Radiator is new and heater matrix thoroughly washed out. Holts radiator cleaner no. 1 added to system and ran, then drained and no. 2 added, so I think the whole system is clean. Have since added anti-freeze. Have not had time to purchase summer thermostat yet, but will do.
Have checked ignition side and that seems good. Have stripped carbs down and all joints from carbs to intake manifold and retightened and applied gasket sealant to ensure no leaks. Blocked off brake servo pipe at intake manifold to ensure no leaks at servo and this DID stop my brakes from holding on for the seconds after braking (see my other thread). Guess I need another servo!
Have re-tuned carbs with gunsons Carb Balancer and Colour Tune along with lifting Carb pistons up a fraction (is it me or is it difficult to distinguish between Bunson Blue and Whitish Blue?). The thermostat for electric fan is about 85c and the engine now runs fairly nicely with gauge needle on N and fan cutting in about 3mm after the N.
So I think all should be well now. I am taking the car down Norfolk the week after next so fingers crossed. The tick-over speed is still about 1500rpm, so I assume this is worn shafts in the carbs which I will have to live with.
Another 'improvement' I have made is from advice from a friend, which you may disagree on - I have cut a hole in the radiator mounting plate on the nearside, where there is a triangular part of the pressing. I did it to try something but can easily block it back up if I need to. I have attached a picture and theory is that it allows fresh air to carb/manifold area to displace the heat quicker rather than just hot air coming through from the water and oil radiators. It seems to work well and appreciate your comments on this.
To end, many thanks to members who took time out to help me with my troubles. Take Care. Pete


Pete Dyble

just thoughts -
great that you used the two part coolant cleaner but I still think you'd need to take the engine drain plug out a scrape out the crud from there (I've seen owners have had to use a drill bit as the crud was so solid there)

personally I dislike those colour things for tuning but others get on with them

hole in the rad panel - the air filters might like it but it might take air away from the radiator(?)

from photo - is that a standard size fan, it looks to cover (block?) a lot of the radiator

what that 90 degree bend pipe about

chrome oil filler cap might not be as good for engine breathing as the plastic originals (if vented)

high idle - dash pots are matched and not mixed and piston drops all the way down
Nigel Atkins

Hi Nigel, thanks for thoughts. What 90 degree pipe are you talking about? There are 3 in photo, brake pipe to servo, vacuum from intake manifold to servo or overflow pipe from radiator cap housing to drain/under car?
Thanks
Pete
Pete Dyble

Hi Peter,

it's the overflow then just looked so big, same as fan, if that's it probably doesn't matter about the sharp bend on it

personally I'd be tempted to put (the latter?) foam strip behind the rad to fill in the gap to the engine bay in the panel to seal the radiator and stop air going over the top as with the bonnet seal

have these for carbs

44 Secrets of the SU Carburettor Part 1 of 2 - http://www.youtube.com/watch?v=7GRAcqDySog&feature=plcp

43 Secrets of the SU Part 2 of 2 - http://www.youtube.com/watch?v=60Bj_2cZQnc&feature=plcp

29 SU H-Type Carburetters - http://www.youtube.com/watch?v=GHNlT5yHDxk&feature=plcp

41 Matching SU Air Pistons - http://www.youtube.com/watch?v=IfU47Oqq9wA
Nigel Atkins

and these - (took me three attempts to 'Submit' to work out I had too many links in one post

123 MG Carburetors & Doors (first part needles and seats, springs and carb oil) –
http://www.youtube.com/watch?v=v9QI3NlvwiY&feature=plcp

147 MG Carburetter Tuning - http://www.youtube.com/watch?v=4nvGLgO6pj0&feature=plcp

Needle and seat - http://www.youtube.com/watch?v=pVX_JClyeDQ&list=FLr4Udxf9e9Cq7fxH4V23MWQ&feature=mh_lolz

Setting the Float Height - http://www.youtube.com/watch?v=82YNx-RkGNI&list=UU40j4KqUJPMVv4FQ29ro-xQ&index=11
Nigel Atkins

Adding to the above, the gauges aren't always accurate and vary from car to car so you might try getting a true reading (jam thermometer in the rad filler is the cheap way, with obvious care). Also, you will want to check the electric fan is pushing not pulling.
SteveP

Which way does your fan rotate? From your picture the cup-shaped or concave side of the blade seems to be facing forwards, is that how they are? If so that means it should be pulling air forwards through the radiator for greatest efficiency i.e. the wrong way, and to do that the blades would be rotating anti-clockwise. If they are rotating clockwise then it will be pushing air through the radiator as it should, but at significantly reduced efficiency, hence significantly slower at pushing heated air out of the engine compartment. Electric fans can usually be set up as pushers or pullers, but both the polarity of the motor and the fan on the spindle have to be set up correctly. Curved blade fans also block significantly more ram-air than straight when wind-milling, and move less air when they are powered. Their only advantage is that they are quieter.

FWIW I've taken under-bonnet temp readings of both mine in the last week or so, 50C in the roadster, 58C in the V8, both during stop-start traffic round town after a run. Running in free air the V8 was 40-45C, the roadster slightly lower.
Paul Hunt

Hi Paul, thanks for interesting point. I have changed the blade around and have attached before and now positions. The blade does touch the radiator slightly so will have to pack it away slightly tomorrow. I ran the fan with thermostat turned right down (engine cold) so I could put my hand down back of radiator to check the flow was correct (push) which it was. I also noted that there was quite a draft coming from around the fan as it does not sit hard up against the radiator, it touches the matrix at the bottom but sits against the upper tank part at the top. I did buy the kit from a supplier at the MG show at Stoneleigh earlier this year and was told it was correct for my '67 MGB. I think it is a 12" (should check but dark now) - have I got the right one? Should the fan cowling fit hard up against the radiator matrix? Options are try it like this, or make some sort of shroud/tube to ensure fit against matrix or buy another one?
Thank you
Pete

Cannot upload 2 photos, so attached a separate one.


Pete Dyble

Pete -- my fan is similar to yours. It also rests against the tank flange so sticks out at the top. I used a couple of strips of self-adhesive black foam weathersrip from the hardware store and closed up the gap. Simple & effective.
Rob Edwards

2nd photo attached
Thanks Rob, sounds good.


Pete Dyble

fan still looks a little over big to me especially for a standard road going car

I should have put about fan/cooling air direction as I was sent the wrong fan, I tested it worked but forgot to check which way the air went, I realised it was wrong from a club run that night

it was so windy the next day I couldn't do a smoke test on it, I found one old birthday card that would blow out in the wind but would smolder for ages so a couple of times I got it burning again and it would blow out again in the wind and smolder again for ages, I wonder what the card was made of

I even checked the Expelair extractor fan we have in the bathroom to give me a clue about blade direction but was told on this BBS about, er, blades, angles, fan impellers, er I can't really remember

I rang the fan kit manufacturer but they couldn't image that it was the wrong fan unit as their dispatched is so careful in checking I practically had to stand on my head with a magnifying glass to read the upside down label set back from the grille - "yes I'd got the wrong fan unit" and "no the fan couldn't turned round or motor wired to drive in the opposite way"

on a Spridget you have to take the rad out to fit the fan and my rad and pipework don't have drains so coolant over the chassis carrying the road grit and muck some into a bowl and the rest over the floor

I also had a BV8 conversion with two fans and when I checked one was going the correct way the other wasn't

so I should have expanded on where I just put check the fan is correct
Nigel Atkins

Hi Nigel, thanks for sending links to youtube, which I had seen most of them apart from: 41 matching SU pistons. I did check mine and chose the best fit drop, but they were still not equal with one having about 1 1/2 second delay. Is this a concern? Car seems to run OK as is or should I look to modify them somehow?
Thanks
Pete
Pete Dyble

Pete,
I'm no expert on anything, I've no mechanic or technical knowledge or aptitude so I watched the JT matching pistons again because I thought JT might have said but he didn't he just said the ones he done were matched and they had half a second difference

not matched were 6 sec and 8 and a half seconds

matched were 6 sec and 6 and a half

so 1 and a half seconds might be a concern for tuning based on those figures but I'm not 100% sure

JT did say it was about consistency so if you put a bit of light oil on the outside of the rod on one you'd need to make sure to put it on the other too - also the inside surface of the suction chamber and the piston need to be clean and dry no oil there

I and any Spridgeteer tried the "90 gear oil" in the dashpot (well he put in 80w/90) and we both thought it worked well with things a little smoother and he found less flutter than he had before at hard acceleration

for tuning remember it's this order - tappets (if rqd) then CB points and spark plugs then timing and last carb mixture

if you have to reset at any step in the chain then you'll also need to check the ones that follow
Nigel Atkins

This thread was discussed between 15/07/2013 and 28/07/2013

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