Welcome to our Site for MG, Triumph and Austin-Healey Car Information.


MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Pressurised Coolant - HGF?

Afternoon everyone.

I tried to run car again today. First of all I checked over all the fluids and it turned out the coolant was low. I followed the procedure to fill it up and it took a lot, perhaps 3 litres. Very odd I though but perhaps there was a leak and it boiled a lot of it. When it ran earlier in the week it ran for about 5 mins and didn't register any temperature as it ran, although after I shut it down and it sat, the temperature did start to climb.

Back to today, filled up coolant, tried to start it a couple of times (it spluttered both times but didn't quite catch) and noticed a leak at the heater tap. So swapped this out for a length of hose.

Re-check coolant. Tried to start it again, cough, cough and no start. Then I noticed that the expansion tank was full to the brim. I then (stupidly!) pulled the hose of the tank and had a gush of water squirt six feet across the garage.

Really confused about what is going on. My only thought was maybe the HG has gone and cranking the engine, albeit only for a few turns was pressurising the coolant system.

Your thoughts are much appreciated,

M Le Chevalier

Does sound like HGF. On a 1500, failure to register a temp on the gauge is often an indication of overheating, which has resulted in a low water level. This leaves the temp probe high and dry, hence not recording the overheating. Combined with your other symptoms it certainly suggests HGF. A compression test would confirm.
Guy Weller


That sorts Monday/Tuesdays task list. Good job wifey is away for a couple of days.
M Le Chevalier

I have an oil leak at the front too, timing cover or sump so I guess it is a good time for a big strip down to solve all these issues at once.

Not feeling the love at the moment!!
M Le Chevalier

I guess the relevant next question is which comes first, HGF or low coolant level. Cause and effect, but which way round and why?

If you were out driving on Thursday then it may well have had reason to get was one of the warmest days l have experienced in this part of the the world. Although it still shouldn't overheat!
Guy Weller

might sound stupid but you've not left a rag or towel in any of the main water way whilst you were doing something with the engine

a work colleague bought a Honda V4 400cc motorbike and part of the deal was that it would come back for a service shortly after purchase - well you can guess what happened and they had to fit a reconditioned engine as a replacement, so it can happen to the professionals too
Nigel Atkins

Hopefully if it needs work its just the gasket or something not to expensive.

Time for a Compression test to get an idea of what's going on.

Good luck and Ill keep my fingers crossed for ya .
Steven Devine

It dosnt sound good,

but id think you would get alot of white smoke/steam out the exhaust pipe, if there is none... id check the oil and see if its a green mucky slime

Try pulling the 4 plugs , placing some card board over the 4 plug holes and then spin the engine over a few times and see if anything and how. Much and what shoots out of the 4 plug holes and onto the cardboard

Then do the compression test

Hopefully the reason it wont start is fouled plugs, and not a warpped or cracked head

Something else, on new hoses, I always go back and retighted new hose after about 200 to 300 miles, for some reason they always shrink down a bit and the hose clamp becomes loose and I spring water check your hose clamps to make sure there still tight before you remove them

If you lost your water that way, then that could be the sourse for how the engine got over heated and popped the gasket or worse

Also did you put a new head gasket on recently, if so did you do a hot retorque after its 1st run

Also are you using NEW arp hardware for the head studs...those have to be pre stretched or they will cause issues as well
Prop and the Blackhole Midget

Also over torqueing is very bad, if the engine calls for 50 ftlbs dont do 60 ftlbs for good measure as that can over squish the fire ring into the cly and cause the problem of over pressuration of the coolent system

Prop and the Blackhole Midget

Yo Prop,

Where would the white/smoke steam come from if it didn't run?! :-) Likewise how would the plugs have gotten fouled?

I am pretty sure the reason for the non-start was low fuel in the float bowl. I managed to nip up the screws on the bottom of the carb another 1/4 turn or so. A slow weep of fuel from there over a few days would have left it low/empty. The mechanical pump on the 1500 is a bit junk wrt priming the fuel system.

I suspect the failure is down to something stupid I did when a. fitting the head. b. filling the coolant or c. running the engine the first time. I will chalk it up to youthful over-exuberance, ensure I am super meticulous this time and not worry too much unless it happens again with the new gasket!

I didn't hot re-torque the head after the first run. Is that still the recommendation? Peoples opinions on this seem to differ.

I have ordered the bits and have a couple of free evenings to do the rebuild as the wife is away. Also sort the oil leak issue whilst I am at it.

And yes, I know you don't add a bit extra for good measure. The studs are so weedy they barely take their recommended torque as it is! :-D

M Le Chevalier

And also, re: all the threads about oils. I have probably badgered my camshaft by now and the head is the least of my worries :-D

mmmm... zinc... zinc, where can I get some zinc...
M Le Chevalier

when refilling coolant do follow the procedure in the Driver's Handbook -
keep the expansion tank end of the hose that goes from rad to expansion tank supported so that it remains higher than the rad as you refill

my advice - pre-mix the coolant and water to the correct ratio before filling (or use pre-mixed) and measure how much you put in so that you know how much you've put in and if this is anywhere near what it should be (allow for residue left from any drain)
- pour in slowly to prevent putting bubbles in
- follow the procedure in the Driver's Handbook

I've never had a problem in the far too many times I've had to refill my Midget cooling system and I'm a total non-mechanic as I just follow the procedure in the Driver's Handbook I know of other procedures/tricks but have never had to use them

as for zinc worry about the issues you have not those that are unproven ;)
Nigel Atkins

Hi Malcolm What did you find wrong . My 1500 is showing some similar cooling issues . Is now overheating and its leaking from the expansion tank with some water hammer noises from the engine bay as well .

Is now overheating and its leaking from the expansion tank with some water hammer noises from the engine bay as well .

Hammer noises ??? ...any sawing noises also ?

Are you sure your hoses are hooked up correctly

Im wondering if there is a bad blockage somewhere and the water is just bouncing off the blockage

Prop and the Blackhole Midget

Water pump going bad, thermostate installed upside down ????


Prop and the Blackhole Midget


Follow Guy's initial advice. When you have done that and reported back then worry about the next steps.
Dave Squire

Dave squire

Malcomes issue are resolved, this thread was revived by a new guest named... "KALY"

KALY also has over heating issues like malc had but with an added ((( hammering ))) noise

Prop and the Blackhole Midget

Hi Kaly,

My head gasket was ruined, simple as! :-)

I think (although I don't like to admit it) due to my own incompetence whilst installing the head in a rush, it barely ran 10 mins before it was cooked! oops!

Two things...

1. I couldn't be 100% sure of myself that I had torqued the head up correctly.

2. I had some sort of fail when filling up the coolant and/or coolant level dropped therefore leaving the temperature sender (in top of the water pump) high and dry, therefore I let the car run, waiting for the temperature gauge to start moving but it never did! By the time I decided something wasn't right it was too late!

More care when re-building and all has been well. Also used a Payen gasket (buy from Moss, they sent me a Payen for the price of a regular HG).

So, in your case, maybe head gasket, maybe cooling system problem (blockage? pump?) do you have any other symptoms? Have you changed anything recently?

M Le Chevalier

Oops :-)
Dave Squire

This thread was discussed between 12/07/2014 and 22/09/2014

MG Midget and Sprite Technical index

This thread is from the archives. Join the live MG Midget and Sprite Technical BBS now