MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

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 MGB Technical - Potential cure for overheating

I was getting my wife's D70 Convertable worked on yesterday and had the good fortune to be seated next to a person who works on building and maintaing MG race engines. I of course asked him about my perennial overheating problem at Interstae speeds and he suggested that I run a Y off the heater hose just after it comes out of the valve and then take this new hose line and connect it to the top of the radiator tank buy soldiering(?) a new fitting onto the tank. He said that this would reduce the pocket of trapped water in the rear of the head and lead to improved cooling. Has anyone heard of this or does anyone have any comments on it. Thanks and remember it is only a few long weeks until we are back on the road here in the senic greater Northeast. Ed Kulick
E kulick

Interesting back ground.

What year is your MGB?
glg

yeah this is even discussed in one of the book's
I've read... bently? about "burping" the block.

There used to be a water tap on the right side
of the block above the dizzy to "drain" the block.

When fillin' the system some folks will let off
the trapped air through the thermostat housing
or the upper heater hose.

There is apparently a condition in the cooling
jackets that allows a pocket of air to be trapped
above the rearmost cylinder. Causes overheating
in that area...

Donno how much levity to give to this tidbit
I'd assume it's a minimal issue since the valve
is nonexistant in the 18v but 'ya never know!

HowY

The head on my 64B is from a 68B but with everything that has been done to it , it probably isn't a factor. I have had done a fast road head, with oversized intakes, three angle cuts, heavy duty everything, Piper 270 cam, engine balanced and trued, Weber downdraft jetted two sizes up, verneer timing gear knocked back 4 degrees for torque ( It was that way before I rebuilt bottom end with no overheating and it gave me much more bottom end, the work which was done on the heads took the power range too high for the type of roads in my area ). There is a new radiator, water pump, fan shroud, electric fan, oil cooler and heater core. The car could idle at 175 all day in 90 degree heat, cruise at 55 up and down hills, but when I start making serious power or go on the interstate at 75 it overheats even with the heater working. There is a five speed installed so I am not running at too high a RPM. I am going to install a Unilite soon to see if I could deal with the advance curve. All help is appreciated. Thanks, Ed
E kulick

Ed, As for something real basic that might help--the standard thermostat for the 18G and 18GA engine is 165. Seems little known but my car sufferered from overheating for years and I tried everything. Finally saw this detail in Bentley's, made the swap and presto, no problems. Hope this helps--would be cheep too.

Paul
Paul Hanley

Ed --

On my rebuilt 18GA, I've had some running hot, 190-200*. Then there was a continual over pressurized blow out fromthe radiator vent tube.

I had fooled around with summer, normal and winter thermostats and finally left the 160* "summer" in.

I do verey little driving once sand and salt hits the roads in winter, and generally wait for a few good spring rainstorms to wash the roads.

Just a guess on your situation, a faulty thermostat, or one that does not work for your particular engine --- (I do believe each engine has its own little personality quirks).

Try a new lower temp rated thermostat. It just may be a matter of an improperly working one that's in there now.

Desperatly seeking a warm spring day,

glg
glg

I have tried a 160 thermostat, 185 thermostst, different sized blanking plated instead of a thermostat and nothing seems to change the fact that when making serious power it runs at about 210-220 . It has to be something stupid because it ran ok before I rebuilt the bottom end. Everything I did should have reduced the friction, therefore some of the heat. I am desperate because I have big plans for the up coming year and an overheating car will put the dampers on them. Thanks for suggestions. ED
E kulick

A cooler thermostat will not make the engine run cooler. The thermostat set the lower limit for the engine temperature. glg, 190 - 200 degrees is not excessively hot, unless it continues up from 200 degrees or if you are running with no anti-freeze in the coolant. The continual over pressure blowout of coolant would indicate a radiator cap that is not sealing correctly or a leaky head gasket (I had that happen on our MGB some time back). I have also installed a coolant recovery system on our MGB, which recovers the coolant that is pushed out when the engine is hot and allows it to be pulled back into the system when everything cools down and contracts. After having a coolant recovery system installed, all the air is eventually expelled from the system, leaving nothing but coolant all the way to the top of the filler neck. By the way, our MGB runs at 190 degrees all the time (I have a 190 degree thermostat installed) except when climing long, steep grades, when it will occasionally get as high as 220 degrees, but no higher than that. Ideling in trafic, even in California, has never sent the temperature above 200 degrees. I consider that this is normal for the car. I personally wouldn't worry about the temperature until it started to head above 230 degrees or doesn't come back down once I have the car at speed on the level. Cheers - Dave
David DuBois

Ed,
Make sure you have good, unrestricted flow through the radiator, maybe by taking it off and running water through with the hose. Also, that the water pump is actually pumping; you should see good movement with the cap off. New parts can be bad.
Since your engine is making more power, it would stress any borderline part of the system. The engine might loosen up some too, running a little cooler, but if everything else ends up looking good, you may need a rad core with an extra row. Best, Joe
Joe Ullman

Ed. As Dave notes, a thermostat governs the lowest operating temperature of an engine, not, necessarily the upper most. I say not ncessarily because it takes 20 deg F before a thermostat is fully open. Thus, it can have a marginal effect, in some cases, on the upper operating temperature due to restricted water flow.

What water-antifreeze mixture are you running? Anti-freeze is only 60% as efficient with transferring heat as water is. Hence, a 50-50 solution, as is often recommended, is only 80% as effective as running pure water. A 75% water, 25% anti-freeze mixture is 90% as effective as pure water, or 12.5% more effective than a 50-50 mixture. A 25% AF mixture seems to proved adequate flow characteristics and corrosion inhibitors.

The addition of the AF to the water will also raise the boiling point as will a properly working pressure cap. A pressure cap raises the boiling point by 3 deg F per one PSI of pressure.

A new radiator is not, necessarily, a good radiator. Check out the archives for more information on this. One way to check to see how effectively it is working is to use an infared reading thermometer to see the actually cooling characteristics of the entire radiator. You might be surprised at what you find.

As to the 200 deg temps. As has been stated, if it is not going much higher than that, you do not have a significant problem. Engines actually wear less at such temperatures than at 160 or 180 deg F. That is why modern cars are designed to run hotter and why the engines show decreased wear as compared to some of the older designs. Les
Les Bengtson

Have you ever descaled and cleaned out the water jacket of the block.

I was surprised to find foundary sand in the bottom of mine.

Once you have removed any such rubbish you can let it soak in central heating descaler for a while.

As I often see on this board, check the standard parts are operating properly before modifying.

David
David Witham

Ed,
I agree with Les, et al. You may not be overheating. Is it boiling over and/or running poorly? If it is just running around 220ºF with no other problems, don't worry about it. I believe the reason older cars typically ran cooler thermostats was because the oils of the day were less temperature tolerant than today's oils. I run a 195ºF thermostat year-round.

Also keep in mind that if you try to keep the radiator full to the top, you will always have some coolant burping out the overflow. Don't mistake this for boiling over. As the coolant heats and expands, it will push a little out the tube if the system is overfull. After a few heating/cooling cycles, the system should reach equilibrium and the overflow will stop. When cool the coolant will be an inch or so down.

In his book "Power Secrets," the late great Smokey Yunick had this to say:
"It is easy to see how overheating can be a problem, but I think some racers overlook the fact that it is possible to 'overcool' the engine. Some guys go to great lengths to keep the engine temperature down to 180 degrees. And, though the engine doesn't overheat, they don't realize that they're putting energy (heat) into the cooling system that could be used to produce power at the crankshaft. Running the engine at 180 degrees will drop the overall horsepower by 2%-3%."
Rob Edwards

Ed,

The "fix" by taking a Y pipe off the heater hose won't work!

The water only flows through the hose when the heater is on and if fitted it would deprive the heater of hot water flow and the head of cool water flow!

Have you drilled out the rearmost water passages in the block? This is an old comps dept trick - the larger waterways were made standard on later engines.

If the overheating problems are real ( and not the guage lying to you) then look to improve the air flow through the rad with shrouding and try removing the seal that runs round the rear edge of the bonnet (hood) opening - but leave some at the sides to cushion and steady the bonnet. The extra airflow ou of the engine bay can have a dramatic effect on cooling ability.
Chris at Octarine Services

Hi all.

My BGT regularly overheated until I moved the front number plate up to the front of the (rubber) bumper, thus improving the airflow through the valance ducts, which were previously partly obstructed by the plate.
Do you have a front number plate, Ed ?.

Don
Don

David Du --

Thanks for that info. I know I'm running a rich anti-freeze mixture probably around 75% to 25% water.

A question I have:

The catalogs say for '62-'67 model years a 7 PSI radiator cap is listed. For '68-'75 , the PSI goes up to 10 PSI.

I have wanted to, or thought about going to the 10 PSI cap to stem the over flow after the car is turned off after a run. That's the only time I get a little blow out -- and it's only that amount I have to refil with water.

Is there something about the early radiators that can't / won't work properly, (or increase MTBF - mean time before failure)?
glg

I modified my engine - including a 5 port alloy head overbore cam etc and installed a 195 degree f. thermostat, 25% anti freeze, and a quart of redline water wetter. Also installed an overflow bottle. I'm using the early model small diameter front crankshaft pulley and the late model water pump with the large pulley, which I estimate reduces the fan & pump and alternator rpms by about 25%. Small diameter, multi bladed plastic fan. No oil cooler. At hi loads on hot days the temp will climb past 200 but no loss of coolant with a 10-12 lbs radiator cap.
Some water pumps have a cast impeller which "looks" pretty efficient. Some water pumps have a crude looking pressed steel impeller which some claim is not as effective. Is your guage accurate? Check to see your ignition timing is not retarded. You could also be running lean which would usually cause pinging, loss of power and overheating. If the radiator cap pressure is low, the steam bubbles will occur not only at hot spots, but also at low pressure spots such as the partial vaccum at the water pump. The consequent cavitation will reduce your water flow and cause worse overheating. Sometines you will see this effect cause overheating at hi loads and rpms get worse when the thermostat is removed and the water pump is moving more water without the restriction of the thermostat.
Barry Parkinson

A 10 lb cap won't make a difference as it will just make the 'boiling point' of the coolant higher. It won't do anything to make your engine run cooler. I recommend that you find someone with an infrared thermometer and have him check the temp of the rad to make sure all the tubes are flowing and the temps are fairly consistant across the core.

An overflow tank would also be nice.
Mike MaGee



One thing that no one has brought up is the water pump sucking the lower hose flat at high speed (hence the spring in many lower hoses)cuting the water supply to the engine. As your problem is only at high speed it might be worth looking at because it does happen.
DENIS
denis hill

glg - If you are running a 75% anti-freeze meiture, that will make the engine run a bit hotter. For best cooling, pure water is the only way to go, but you need the anti crossives and water pump lubricant that is in the anti-freeze, so a 25% mixture is the minimum that is recommended. I run a 50% mizture and don't have any problems, but then I don't live in a deepfreeze like you do :). Regardles of the pressure of the radiator cap, you will loose coolant when you fill clear to the top. The coolant expands when hot (particularly when the car is not moving to provide cooling air flow) and when it expands and builds up sufficient pressure, it will unseat the primary seal of the cap and push the coolant out the overflow hose. A coolant recovery system as I stated previously, will catch the overflowing coolant and return it to the system when everything cools off. If you will send me your e-mail address, I'll send you pictures and a more complete explanation of the workings of the coolant recovery system. Cheers - Dave
David DuBois

My car runs at about 190 degrees and it climbs to beyond 220 when I have the air-conditioning on. This is especially so in the afternoons when it is hottest. In the evenings it sometimes will take longer to get past the 220 mark (with airconditioning on).

I dont know what I need to fix to keep the engine operating at about 190 or slightly higher with the air-con on.

Been running on water.. but have also tried coolant. No real difference except that it does take noticably longer to get past 220 with the coolant.

There is a leak... and I notice it when the car has been parked for between 20 mins to an hour... curiously enough I dont see the leak immediately after stopping. This I have checked. Wondering why I don't see it immediately.

The radiator is definately leaking (as I see coolant collecting at the top and bottom of the radiator) but I am not sure if thats the only source of the leak. The Water Pump may also be leaking. Checked looks OK, but what do I know ?

Does anyone have any ideas ?
sudhir menon

Ed-
I think that Denis may have hit upon the origin of your problem. With the engine cold, reach down into your engine compartment and compress the coolant pump intake hose. If you can compress it much at all, then it's almost certainly compressing at highway speeds, restricting coolant flow. Chris's mention of the old MG Factory Race Team trick of opening up the two rear coolant ports at the rear of the block and head is a good one. Using a 9/16" (.5625") drill, simply open them up and then lightly chamfer them to be sure that you won't be interfering with the sealing of the head gasket. I do this on every 18G through 18GK Series engine that I build. The 18V engines already have this larger porting.
Steve S.

The hoses alomg with most everything else are new. The new hoses are of the type with the wire inserts. Opening up the block sounds like a good deal and I will try it. I have some time before spring. I don't know if it is the problem though as the only time it overheats is when I am making power. I am thinking that my mech distributor might be over advancing so I am in the process of putting in a Unilite so that controling the advance curve will be a little easier. I am desperate as I am down to grasping at the chafe below the straws. Ed
E kulick

Have you verified the temperature with a kitchen thermometer?
Dan Robinson

IME retarded timing causes hotter running rather than advanced timing - unless it is very advanced and you are ignoring pinking. With no pinking it isn't going to be much overadvanced if at all.

But if it isn't losing coolant it isn't 'overheating' in the true sense of the word, even if it is running higher on the gauge than you would like. Before I fettled the cooling system of my V8 I have seen the gauge right up in the red - which is a small bit of the scale right at the end - when stuck in traffic in ambients of high 90s, with nothing more untoward than a bit of a rough idle.

Paul Hunt

Paul, If I understand you correctly, even though the temp gauge is reading 220F for a short period I am doing no harm to my engine as long as there is coolant in the system. I have installed a collection tank and put the drain tube in it. It will eventually fill the tank ( app. 1 1/2 qt. ) but not return to the system. I believe that I know what that problem is and am in the middle of correcting. I have used a thermometer on the radiator, and it has shown a lower temp than the guage, but the guage reads the head temp and not the radiator temp so I would assume that it would read lower. I have installed a five speed so even though I am traveling at 70-80MPH I am not over reving the engine. With the cam timing at 0 I had no low end at all, by retarding the timing 4 degrees I have am automobie that fits the roads which I travel, very hilly,, very twisty and , for the Eastern US ) a higher elevation-2200'. Do you believe that the 4 degrees is an excessive timing retardation? Thank you very much for your time and consideration. Ed
E kulick

Retarding cam timing reduces low rpm torque and increases hi rpm power. Retarding ignition timing can cause overheating and loss of power. If you fill up with cheap fuel and advance the ignition timing to a point where it begins to ping under load, you are very close to optimum timing. You can then choose to retard the timing slightly or go to higher octane fuel to avoid the pinging.
You should check your distributor advance curve. Many later distributors have mechanical advance that comes in at a relatively hi rpm. You could be cruising at 2500 rpm at low vacuum (no vacuum advance actuated) and without the full centrifugal advance, resulting in retarded timing and overheating. The early model distributors have much better vacuum and mechanical advance curves.
Barry
Barry Parkinson

I am surprised that no one has suggested thermostat design as a possible source of this trouble. There is information in the archives on this.
The MGB head has a large port just below the thermostat to allow coolant to circulate through the engine with the thermostat closed. With the original design, this port was gradually closed off as the thermostat opened, forcing the coolant to circulate through the radiator. Since this part is NLA and the newer stats seem to have a smaller flow area, the coolant takes the path of least resistance, only a part of which is through the radiator. Racing applications use a blanking sleeve which closes off all but a one-eighth inch diameter area of this port.
henry rebman

Ed - continually pushing coolant into a catch-tank *is* a problem to be concerned about. All the (UK) rad caps I have seen have a double seal - the rubber seal at the bottom of the filler neck and a spring-steel seal at the top, the overflow tube being positioned between them. With this top seal, and the low-pressure valve in the rad cap that opens when the system is cooling means that any coolant pushed out during warm-up *should* be sucked back in again on cool-down.

If it isn't then maybe the upper seal is missing or leaking (or your overflow tube doesn't reach to the bottom of your catch-tank). However that would only push out any excess, after that there should be no more loss.

A couple of years ago my factory V8 started pushing coolant out constantly due to bubbles forming in the header tank until eventually the coolant level dropped so much that it *did* start to overheat - if I let it get that far. A lot of diagnosis didn't really prove anything, including specifically testing for combustion gases in the coolant i.e. leaking head gasket, so I did a top-end rebuild just to see if I could find anything. The only thing I did find, and it would have been so easy to miss, was that the thermostat bypass pipe that runs *inside* the inlet manifold (not the heater return pipe running underneath) was fully or partially blocked, although how this could be applied to a 4-cylinder is anyone's guess. Simply clearing this stopped the coolant loss and incidentally significantly changed the warm-up characteristics on the gauge, and it now runs noticeably cooler on the gauge.

One of the diagnostics that showed me *what* was happening, but not *why*, was a coolant pressure gauge. I could see this gradually rise up to the pressure of the cap, no matter what cap I fitted. The standard was 15lb and I tried a 20lb. This delayed the onset of true overheating slightly but that was all, and eventually the bottom hose blew spectacularly. Now the pressure only gets up to about 11psi just as the electric cooling fans cut in, dropping to about 6psi by the time they shut off again. Running in free air shows about 4psi.

On my roadster retarding *ignition* timing just 1 or 2 degrees from normal (10 static) when I had to run on low-octane fuel in the wilds of Scotland, was enough to sap power and increase running temps noticeably. I'm a bit confused at to whether you are changing cam or ignition as you mention both.

With the stat fully open there should be a strong flow through it into the rad and therefore I would have thought the difference in *coolant* temperature between head and rad header should be minimal. However being metal and screwed into the head maybe the standard sensor is picking up additional temperature that has come from round the combustion chambers and not yet got into the coolant, which is why coolant temperature (and pressure as I noted) rises after switch-off.

Paul Hunt

Paul, I am in the process of repairing the collection system, the overflow tube coming from the radiator is loose and needs soldiering, and the cap is a single seal type, I am going to remove the head today and ream the rear water passages out. The timing I would like to leave alone at this time because it works. If the other two remedies don't work I will revert to traditional timing and see if that does anything, but at this point my auto runs very, very well so I will reserve that as a last resort. I wish to thank you and all other posters for the consideration that I have been shown. Ed
E kulick

Here's a page about the thermostat Henry was talking about. Although a dedicated MGA site I highly reccomend looking through the rest of this site if you haven't done so already. There is much information that can be applied to our Bs.

http://www.mgaguru.com/mgtech/cooling/cool_103.htm


-Jared
Jared Snider

Ed, you mentioned that your radiator is new,
but check the archives, many of the new rads are
not of good quality. (I had this problem with my
79 B -- getting really hot past 50 MPH or so.) The solution to your problem may simply
be to get a more efficient radiator core.
Some have recommended the Modine "L" core, I'm
using a Godan "MX" core with extra wide tubes.

I would take your radiator to a good local shop
and have them examine it and flow test it. A recore
is probably the best option.
Ronald

This thread was discussed between 29/01/2004 and 09/02/2004

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.