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MG MGB GT V8 Factory Originals Technical - V8 Overheating

I have recently bought my first MG a 1973 Factory V8.

I know they are notorious for overheating but is it normal to have to keep the heater on to keep the temperature at normal?

I had a full inspection performed and I was told the cooling fan motor was getting worn and assume this should be the first thing I replace. There was no mention of radiator problems but I guess I should get that checked out too.

I don't have the knowledge to perform my own repairs(yet), so will be taking the car to a garage to rectify this problem.

As the saying goes forearmed is forwarned so any advice most welcome.
Paula Cottle

Hi Paula,

Always good to see another V8 in town. My experience of running a V8 in London as my only car for the last three years is that the cooling is fine as long as the system is well maintained. What do you mean when you say you have to keep the heater on to keep the temp at normal? The system is actually designed to heat up to about halfway between Normal and Hot, then the fans should cut in and bring the temperature down to to about the Normal position before they cut out again. Is this what it's doing or is it heating up and boiling over? If you want to get your garage to give it a once over then get them to flush the sytem out and fit a new thermostat and pressure cap which shouldn't be too expensive.

Have fun

Philip
Philip Shingler

Philip,

The previous owner advised me to keep the heater on at all times and switch the cooling fans on when it reached normal. He did advise me the cooling fans will cut in between normal and hot but that wasn't ideal and it was better to keep it running cool.

I've done no around town driving yet but on a long run once the fans are switched on the car does stay at just above normal. So no it doesn't heat up and boil over.

I guess it comes down to individual owners and the way they drive, so I'll just run it as you suggest, no heater and let the fans cut in and then see if I really do have a problem.

Many Thanks,
Paula
Paula Cottle

As Philip says, just let the fan stat do its job, although in my case it cuts in just above half-way between N and H and cuts out just below that point. If you look on the edge of the painted scale you will see two little white dots that correspond to those points. However I would recommend fitting an illuminated manual switch (although it sounds like you may have one) to the fan relay, that way you can see when the fans have cut in (although I can hear mine) and you can overide it if you need to for any reason. Much better than having to have the heater fan blasting away in summer, it gets hot enough inside as it is.

I also have an uprated radiator from Clive Wheatley which makes a significant difference to the cooling, although the real problem is not so much getting the heat out of the rad as getting the hot air out of the engine bay - there is no problem maintaining N when driving, only when stuck in traffic on a very hot day. On the old rad with temps in the 90s the temp gauge would still get into the red in traffic even with both fans running full time. Didin't boil even then, but did start to idle roughly.

I think the previous owner was just paranoid, although it is just possible that he/she was covering up a hot-running problem. Does the fan stat and relay work as it should, i.e. cut in and out and maintain the gauge between N and H when idling (bonnet shut)?

PaulH.
Paul Hunt

P - almost all the advice you need is here already
the car will run properly on the hottest days provided it is well maintained. There is just one maintenance schedule that is not in the manuals: - that the core of most radiators has a natural life of 5- 8 years and in the case of the factory V8 you get it changed when you have to drive with the heater on (yes we have all done it at sometime).
The good news is that the new core should come with a lifetime guarantee - (they change for free next time)

When this has been done, your driving style will not change the temperature much - the temp under the bonnet will always be hot - carry a spare coil and plug leads et conduisez vous avec le panache !
R
Roger

Some time ago I saw a discussion about timing and its effect on operating temperature. Don't remember the details, but by varying the timing a few degrees one way or the other it was said to be possible to reduce the operation temp by 10 degrees or more without affecting mileage or driveability. Does anyone have experience with this?
Caveman

Timing will affect coolant temp.
After getting my MGBGT V6 (Buick 3.8) on the road, I would get high temps on the interstate. Tried everything to bring temp down.
I later discovered that the HEI distributor had nearly a quarter inch of end float! This came to light when the cap wore out in a week...
I could set the timing at low RPMs, but as the revs would climb, the shaft was "unscrewing" itself and retarding the timing.
When I replaced the HEI with a Mallory D/point the temp would then stabilize just above the normal mark (unless really pushed HARD).
Randy
Randy Forbes

Caveman - I think it is more the other way. Retarding or advancing the timing noticeably from spec will *increase* running temps.

PaulH.
Paul Hunt

Are the products such as "Cool Water" any good ? I understand these to be an additive to the radiator water which raises the boiling point of water and / or simply lowers the temperature of the water in the radiator somehow.
James Read

James, I think you may mean 'water wetter' which works by reducing the surface tension of the water thus increasing the flow of heat from the water to the radiator. Yes, other contributors to the BBS have strongly recommended these products, but you need to ensure the rad and hoses are all in good nick as it's expensive stuff and you do not want to lose it or have to drain it.
HTH
David Smith

Well I tried "Water Wetter" this weekend and it hasn't made much of a difference albeit that I only drove it once after putting it in the expansion tank. Maybe it needs longer to fully get into the system ?

My car's normal running temperature is up to the first dot on the guage and when the fan comes on it then goes down to a little below this. It never runs at normal (i.e. six o' clock position) but also never goes above the first dot on the guage. I am learning that running hot may be "a feature of the model" but is this beyond what would be considered normal by anyone driving a V8 ?
James Read

Watter wetter does work, but in a system that is coping with the peak temps reached, and yours does seem to be in this catagory, you won't see any reduction in the normal running temp as the thermostat controls this temp.

The speed of temp change from normal to the fan cut in point should be reduced and take more time, and when the fans cut in you should see a faster reduction to the fan cut off point.

The MGB body and V8 engine does no favours for airflow through the radiator, and this is a major problem in keeping the V8 cool.

Rog
Roger Parker

Only driving the car once after putting water wetter in the expansion tank will do nothing, for it takes at least one heat/cool cycle to draw at least some of the fluid you added to the tank into the circulating system, and you will only be able to add a small amount. Was there a recommended application rate?

When cruising at any speed over 30mph and not tailgating another vehicle the temp should come down to N. Sounds like your gauge and electric fan switch are in agreement, have you tried changing the thermostat? Have you tried draining some fluid off - it is clean?

I installed an uprated radiator from Clive Wheatley - some 30% more cooling area - and it does make a difference, however as Rog says the real problem is getting the hot air out of the engine bay. Just compare how long and how often the fan cuts in when stationary with the bonnet up compared to bonnet down.

Incidentally, I feel far more comfortable (and so does the car) with the Burlens replacement for the Otter fan switch. Mine was getting a bit iffy anyway and drifting above the two little dots, but the new switch keeps it between N and the first dot. Virtually doubles the hot idle oil pressure. Only minor niggle is that it seems to experience heat soak and if you get the car fully up to temp, switch off and restart a few minutes later the fans come on but don't go off again until the temp has got right back down to N, sometimes even later.

PaulH.
Paul Hunt

Water wetter is starting to work. In traffic, the fans bring the temperature down to a about a third of the way between 'N' and the first dot.

Checked my expansion tank and the colour of the water (after inclusion of water wetter) is brown. Guess I need to have the radiator flushed ?
James Read

James, hence my previous comment "but you need to ensure the rad and hoses are all in good nick as it's expensive stuff and you do not want to lose it or have to drain it."
this includes flushing it !!!!
David Smith

Like it was stated Watter Wetter does work. The timing goes together with fuel mixture, both contribute to the cooling system performance. On a FI is very criticqal to change the Ox sensor, when dirty it will lean or richen the mixture depending on the system. On GM it will richen the mixture and the system will retard the ign. thus creating hotter temps and bad fuel mileage= bad performance. On carb models the fuel mixture and timing are critical to performance and temp control.

Paula, cheap insurance When buying a used car is to replace water pump, replace hoses, service radiator, replace thermostat, replace belts, test electric fans or fan clutch, condition of fan blades, and flush the system completly. Also do a complete brake job, and a mayor tune up. It's a piece of mind and will enjoy the car more.
Used cars sometimes look good becouse the engine bay was detail, but...what is the real condition internally. Unless the previous owner has documentation, if he does, then match the miles with odometer and paper work. Famous words "Just did a brake job not to lon ago" Yeap!!!

r/ Bill G.



Bill Guzman

David,

Thank you for quoting verbatim from your earlier message. Good advice though it was, I took the decision that I could just about afford the £7.95 it cost me to try water wetter and still have money left to buy it again if I decided to flush my radiator (I haven't yet). I don't know what you are pouring into your radiator but water wetter is not that expensive !

James
James Read

Wouldn't have thought WaterWetter would have changed the colour on its own unless it is like ForLife fluid which does run brown and changes colour if you have a head gasket leak.

PaulH.
Paul Hunt

James,
now that IS good news - brand and source please ! . Last time I looked this stuff was 15 to 20 quid a bottle depending on supplier.
David Smith

I threw the bottle away so I don't know the brand name but I got it directly from the MG Owners Club in Swavesey. I remember that it said "Water Wetter" on the bottle.
James Read

Thanks.....
David Smith

Hey, here's something simple that helped me.

My GT V8 conversion has always had a problem with running hot, but the problem really only existed when the car was standing still or moving very slowly. No problems at speed.

I was unwilling to modify the exterior of the car from its bone stock appearance, and so hood louvers and vents were out. With the engine being in and all, it's awfully hard to do a decent job of installing inner-wing vents, and besides (i) they don't do much if anything unless the car's moving, and (ii) they expose the engine bay to too much road gunk.

I looked at the engine bay for a minute and a bell went off. I just drilled a hole (1-5/8"? 2"? I can't exactly remember in the firewall right next to the heater. IOW, if you are looking rearward at the engine bay, the heater unit slopes down from left to right -- on the RHS and just above the heater unit there's an area of sheetmetal that connects the engine bay to the fresh air box. I installed a piece of screen in there, and made up a finisher so it looks fine. This is the highest point in the engine bay, so it's a perfect place from which to relieve the buildup of hot air under the hood.

Now the ventilation of the motor when the car is not moving is much better, and the motor temperature at such times is markedly lower. At a red light, you can see the hot air burbling up out of the fresh air box. Plus you probably get _slightly_ better induction, since the carb can yank a little cold air through this hole (it's certainly not big enough to make much of a difference -- if you were serious about this you'd take off the heater and drill a big hole, but then I think the size of the fresh air grille would quickly limit the benefits).

To be sure, this is a positive pressure area when the car's at speed, so you're not helping cooling at that time. However, if you're like me, it's only cooling at a standstill or moving slowly that is the issue.

I hope this is useful information.
Tim Brockett

It's an interesting concept. I am surprised you get much difference even with a 2" hole given the heat that is coming out of the rad, and the drawback is engine bay fumes are piped through the ventilation system into the car when running, I would've thought.

We've had temps of 32/92 today and I took my factory V8 with uprated rad for a motorway blast then a crawl through stop/start traffic for a couple of miles. Once the fans came on it stayed on, but they kept the temp needle to about one and a half 'N' widths above normal.

PaulH.
Paul Hunt

This thread was discussed between 17/05/2000 and 19/06/2000

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