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MG MGB Technical - How much coolant?

My coolant is brown and disgusting. The engine is running hot, partly cause its running lean at the moment. Its the only way I can get it to idle any way close to under 1000rpm. Anyway I need to replace my coolant, and although it looks like a nice handy job (you try doing it on a Volkswagen!) I want to get it right. Firstly, how much coolant does the system take (preferably in litres)? Also, what coolant should I use? Is there anything else I need to know aside from open the taps, drain the coolant with the heater valve open, close the taps and fill it back up with a 50/50 mix of rust inhibiting coolant and water again?
Ross Kelly

Hi Ross,
First we need to know what year MGB you have are differences in filling up the coolant system.
Second we need to know what carburetors are on your engine to answer your question.


James

Its a 78 UK spec car with SU HIF4 carbs. Why does it make a difference what carbs I have?
Ross Kelly

I usually buy 4 litres of coolant (Prestone is a good brand), and fill a pitcher half full of coolant and fill the remaining half with water, and fill the system with that until it is full. I think the pitcher I use is about 1 to 1.5 litres. Invariably I will have alittle extra left in the pitcher when its full, which I have transferred into a small container and keep in the boot for emergencies. I don't recall exactly the amount it should take, but it probably depends if you have managed to drain all the coolant from the heater core and the lowest inch of the block.

I'm not sure how much difference carbs would make, although maybe with Zeniths, the water choke adds to the capacity? I wouldn't think it would add much.

Your car may be running hot because of clogged coolant passages rather than the lean setting. If your coolant is that brown, maybe it was just simple water, which would cause significant corrosion inside the system, which in turn may cause the radiator to be restricted. It would be a good idea to flush the system with either water, or some solution designed for it (others may be able to recommend). Open the heater valve. You might even consider taking the rad to a rad shop and have a valve installed in the bottom of it, for easy fluid changes in the future (sure beats taking the bottom hose off the rad and letting the fluid pour everywhere except the container you're aiming for).

Also note that pets love the taste of coolant, but it is very toxic/deadly, so don't keep it where animals can get to it.
Erick Vesterback

Ross,

From Porter again, cars up to no. 410002 5.6 litres, from there 6.8 litres, both including heater.

I'd be careful with your coolant mix percentage. I know you will have to protect to a level dictated by the temperature you can anticipate where your car will be 'living', but that stuff has a very high 'slip' factor and can find gaps in head and thermostat gaskets you don't otherwise know are there.

Given youe description of the coolant condition presently there, might you consider a lower percentage than 50 for a start? Your summer approaches and a mix around 20/25% will provide protection against rusting whilst giving you a chance to test the soundness of existing gaskets.

Regards
Roger
Roger T

Thanks for the info. I think I'll do this this weekend. SO a later car wont have the valve in the bottom of the rad then? OK so, well I'll pull the hose off the bottom then. A new rad was fitted to my car at some stage as well, so I dont think it will be too bad in fact.
Ross Kelly

Ross - the rust colour suggests the inhibitor has broken down / perhaps wasn't replaced at the rad change - suggest you fill with clean water and run at normal temp for a while - cool before changing a second time and adding coolant.

Roger
Roger

Ross. Please go to my website, www.custompistols.com/ and click on the MG section, then articles. The one you need is cooling system inspection. It will discuss percentages of anti-freeze to water, the need to use distilled water, or purified water at the very least, and the need to flush the cooling system before installing the new coolant mixture.

Roger is correct that your rust inhibitor has broken down, the interior of the block is rusting, and, if not flushed, will form a barrier to efficient cooling. Some of the "sludge" will have gotten into the radiator and will cause further problems unless throughly cleaned out.

Les
Les Bengtson

Ross,

First you need to flush your system as Les recommends!

I run my coolant at about a 33% mix, it cools better than 50% and it's easy to get there. The cooling system holds about (just under) a gallon and a half, so if you pour in a gallon of water, and add coolant to top up, you'll be close. 10 minutes of running will have it thoroughly mixed, you don't need to pre-mix.



Paul K

Paul,

I agree one doesn't need to pre-mix (ordinarily) but in Ross's case I'd be concerned about concentrations of coolant (or more correctly, the glycol component) getting through gaskets, hose connections etc.

In this case I'd recommend premixing and at an initial lower concentration. Ross could always work the mixture concentration upward over time - perhaps approaching next winter.

Regards
Roger
Roger T

The figures quoted for volume are always for dry engines. When draining and refilling this is never the case, and if you pre-mix and fill with that you will end up with a weaker concentration. Put some water in, then all the concentrate required calculated using the dry volume, then fill up with as much water as is necessary. You might need two or three heat/cool cycles to get all the air out of the system, it is fine to add just water for this topping-up. After that only ever top-up using the correct concentration i.e. pre-mix it.
Paul Hunt 2

Thanks for the help. I picked up 3 litres of coolant today and some coolant flushing stuff so Im going to take care of this job this weekend.
Ross Kelly

Paul,

Well!

Using dry volume is OK if you can be sure the water passages are not afflicted with sludge (particularly in the block floor around the chambers), blocked passage sections, casting sand remnants or internal casting variations to water passage spaces. In that sense, there can never be a sense of exactness about volume. It is always an approximation.

Both our approaches requires only basic arithmetic.

My concern with concentrated coolant in this case derives from the described state of the present system and the prospect of Ross using a descaler. In my experience (and it was in respect of a newly installed gasket under a rebuilt head)the internal edges of head and thermostat gaskets will need to be in very good condition, and the thermostat housing stud bottom threads not significantly compromised by corrosion or looseness if concentrated coolant (glycol) is not to work itself through.

Hope it all works out Ross and perhaps my concerns don't apply regarding the condition of your motor.

Regards
Roger
Roger T

Blockages in the system from sludge or scale are different to the effects of water remaining after a drain, or from flushing. With the former you *should* be able to fill from 'empty' using a pre-mix and get the correct concentration, you just won't get as much in as expected. With the latter the concentration will be less than expected, and the quantity even more so. When buying concentrate it is so much easier to put a given amount of that in then top up with water till the system is full, compared with getting at least one clean and empty container to dilute some concentrate and put that in, then dilute another lot and so on. With 30% solution the level shouldn't be up to the head gasket anyway.

Going back to the original 'brown and disgusting' comment I think ForLife (ready diluted) looks like this anyway and is not intended to be changed on a routine basis, so it could be that rather than brown and sludgy water, especially if it has that appearance when left overnight. Sludgy water is more likely to be 'brown and disgusting' immediately after running, less so overnight.
Paul Hunt 2

Hi Guys,
The reason for asking what carb or carbs you have was because of your statement of your car running lean and not being able to idle below 1000 rpm. That is your underlying problem.
Now with 1978 cars at least US Spec, there is no radiator cap, you need to take the top hose off of one side and pour in coolant till it starts running out of the radiator or the top of the thermostat housing, which ever you pulled. Then you need to fill up the coolant reservior. Then start the engine and purge the system of air. You can aid in this by squeezing the top and bottomw radiator hoses which will speed up the process of the coolant system drawing in coolant from the reservior.
Although I love the information, I think you guys are getting way too much into this. Buy a bottle of coolant, get pre mixed 50/50 if you dont want to be bothered, and if you need more, go out and buy another. As for flushing the system. Get a hose and stick it in the top radiator hose, disconnect the bottom radiator hose as well, have something to catch the coolant and water, and then spray.
James

James. It is quite possible that "you guys are getting way too much into this". However, I might point out that those of us have been doing this for 30-40+ years do have some experience with such matters, both good and bad. Hence, the advice to flush the cooling system, throughly, including the block where rust forms and deposits collect, is based on that experience. Your method runs water through the radiator, providing a minor cleansing effect. Our method, if used, cleans out the system and goes to the area of primary responsibility for the formation of rust particles in the coolant. Both systems will work. But, our experience is that the latter will work much better than the former system.

Les
Les Bengtson

Gooday all - just to add the comment that there is no such thing as too much experience being passed on by some, for the benefit of others! - James, I've only been fiddling for about 25 years, and have so much more to learn, it's not funny. If a "threader" asks what I think is a simple question, I often compare my knowledge with that of respondents, and frequently I find the collective advice constructive and, importantly, never condescending or judgemental. I'm sure Ross has benefited from all comments, including your own.
John Hall

Absolutely! No one persons advice will be followed to the letter but I will use the info I have gained collectively from this thread and Im sure it will make my life easier and my cars engine cooler.
Ross Kelly

I got the coolant replaced today. Wasn't all that complicated, but the water that came out was unbelievably disgusting. The bucket I used had a load of silt in the bottom when I emptied the coolant out. I took off the thermostat housing and while it was off I made a new gasket for it cause the old one was a mixture of rubber sealant and mashed up paper and wasnt all that effective. I took both the top and bottom hoses off the radiator and flushed both the engine block and radiator through until the water ran clear. I used some flushing agent as well. The whole job was much easier to do with the thermostat housing off. I just filled the block, filled the radiator and filled the header tank, ran the engine and it was fine! It doesn't overheat any more and sits perfectly between hot and cold. I also soldered shut the poppet valves in the carb butterflys. Tricker job than I would have thought. It was a nightmare to get the solder to stick, despite the fact that I cleaned everything thoroughly. I ended up in the end just removing the cap that kept the spring in place by twising it off. I sanded everything clean and then it soldered up nicely. So the carbs went back in, I adjusted them up which was much easier this time and the car now idles at 800rpm, which is great. I redid the ignition timing and now the car is running great! So I'm delighed! Im still going to replace the carbs though and I want to fix the overdrive. Ive also to get some hose to connect up the vac advance. All to be done over the next few days! At least the car isn't overheating anymore though!
Ross Kelly

Well done and a great outcome. I respect the way you have gone about dealing with the frustrations encountered. Drive and enjoy your car, you deserve to.

Regards
Roger
Roger T

Hi Everyone,
Didnt mean to ruffle any feather here and reading back my statement was very generalized. But 33% coolant mix? and casting sand reminates? I just thought it was funny how it got that involved and everyone basically ignored his carb problems which in comparision is a bigger problem than your coolant mix is all... Ive been on this site for at least 10 yrs and always appreciate any knowlege obtained here. Hope you dont think otherwise.

James
James

Well James, I didn't think you were ruffling any feathers. I'd be inclined to think though that an overheating engine is a far bigger problem than the carbs being out of whack. In the short term one will do far greater damage than the other. Besides, I can do nothing about my carbs until the new ones arrive.
Ross Kelly

yea, it just all depends, the running hot could have even been attributed to your timing being off, etc etc etc Glad you have her running a lot better
James

Yeah youre right, the fact that the car was running crap didnt help matters, and in a way I tackled the symptom before the cause but the symptom was liable to do a whole lot more damage.

Anyway to answer my original question... 6 litres. Thats how much it took to fill her up. Nothing in comparison to the 16 litres that my volkswagen camper took! A much easier job too I might add. In general I have to say MGs are fairly easy machines to work on. Especially in comparison to VWs, where everything is either totally inaccessible or the engine has to come out to do anything with it.
Ross Kelly

This thread was discussed between 01/04/2008 and 07/04/2008

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