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MG MGB GT V8 Factory Originals Technical - Overheating

I have finally got my car on the road and am now cursed with an overheating problem. I have a 3.4l engine and am using the stock radiator with modified inlet/outlet. I tried replacing my single 10 inch fan with dual 8 inch fans on a relay. I also added Forty Below (its like waterwetter) to the water. I tried removing the thermostat, but the temperature still hits 230 even while driving. I believe that I need to make my radiator larger or just buy a larger one. Does anyone know off a radiator that would fit with both the inlet/outlet on the driverside?
Shawn Kennedy

Most radiators can be modified to have their inlets and outlets on either side as desired. I just put in a radiator from a 1965 ford falcon w/289 V8. Took some modifying of the mounting tabs on the radiator, but it fit just dandy.

What year is your car? Is it the 3.4L V6? I've never heard of those having overheating issues. How's your timing? That can drastically affect heating.

Food for thought,

I know it may be a long shot, but you might want to take the temp yourself with a candy thermometer. I have found that sometimes gauges can read wrong. On my BGT, this was the case, gauge always said way too hot, but when I took the temp with the candy thermo. it showed that it was normal. HTH.

It is a 1975. The engine is a 2.8l v6 thatís been stroked to 3.4l with race cam. The timing appears to be close and the car runs great. As for the temperature I have verified it with two different gauges and the radiator begins spitting water out the overflow tube. Is the Falcon radiator worth it or would changing the core in the original be better?
Shawn Kennedy

I can't tell you whether or not it's worth it, because I haven't driven the car with the new rad yet. (It's currently snowing here, and we're gonna get around 6".) A few more questions for you: Do you have a fan on the motor or just in front of the radiator? Fans that pull are about 20% more efficient then fans that push air through the radiator, so that may be an area to look at. You can recore an mgb radiator to a 3 row, from a 2 row, and do a high density fin pattern. That will help with cooling too. BTW, the falcon radiator is about 4" longer then the late model B, so you have to be careful how low you let it hang.

Take a look in the archives. There is TONS of info about cooling in there.


230 _is_ getting a little up there. It does this even while moving? ... I mean lots of these hot rods heat up quite a bit when standing still but at speed it's overheating is pretty unusual. Are you sure your pushers are turning the right way? I had tons of luck when I had the rad re-cored at a place that built radiators for heavy earthmoving equipment. It cost a fortune, but that car now stays cool. An air dam greatly helps -- yes, I know, kind of ugly -- because it creates a bit of suction under the car that helps pull the hot air out of the engine bay. Some of the guys have had luck with alu rads but ALL of the stock car boys down here tell me that they scale up very quickly and hugely lose their effectiveness unless flushed out absolutely constantly. So I don't know if I'd recommend the alu route.
Bill Withum

Here in SoCal. summer temps. frequent 100+. I've built many "heated rods" and usually have my stock radiators rebuilt with 4-row high efficency ones. Cost is around $150 - $200. My radiator shop sometomes spreads the tanks to accept thicker than stock cores. This works a treat.

The hot air also needs to vent from the engine compartment. Side vents and hood louvers look neat and can help significantly. Also exhaust fan/s can be installed into the wheel wells.
Stay COOL! M
Marc Judson

shawn, glad to here that your car is on the road, i have the sam eengine in mine with the stock 1978 mgb rad, when i first assembled mine i installed an oil cooler an di took it out because it ran to cold, 160 or so even with a 180 ther, when driving on the highway, i use the stck twin fans and i have never had a heating problem, i even took the header wrap off mine, i have put in a hotter cam and some other things and i am thinking of maybe going back to an oil cooler this sumer , i will see. i would think that maybe you should take the stock rad in and hav eit dipped and cleaned, i did this to mine when doing the conversin and there was lots of crud from 20 plus years of use, i do no tknow anyone else with a 3.4 that has had any heating issus either, are you using an overflow tank?? i still use the stock one for mine, jim
jim m

The radiator was recored last year and since no one else seems to be having overheating problems there must be something else wrong. Maybe the water-pump is shot or I put a head gasket on backwards. As much as I hate to do it, I guess I will have to start tearing things down until I find the problem. Thanks guys for all the feedback.
Shawn Kennedy

Shawn, you and the others have brought up good pointers to search out. The V6 overheating is not a common thing at all, so you have me, however, here are my two cents:
1st- pump itself has pulleys that turn it one direction when it was supposed to turn the opposite way. (IE- a pump that originally had a pulley that rode on the back of the belt and now you may be using the kit that turns the opposite direction)

2nd- timing cover is the wrong unit for your water pump. If you are using the cover that pushes water in one direction and a pump that turns it the opposite, you are Cavitating <sp?> the Pump (may be turning the opposite direction of what it is supposed to) and therefore your water is flowing from the top of the radiator to the bottom. Opposite of what it is supposed to. This would be a severe cause for overheating as you are stating.

I currently have a V6 in house that another shop started working on 5 years ago and never finished. Supposedly a LT1/LS1 shop and they missed the fact that they welded the V belt pulley to run the opposite direction of the sepintine belt pulley they have it welded over! Unbelievable how little things like that can be overlooked so easy.

As much as a big radiator sounds good, and never hurts, look at all the other issues first.

BMC Brian McCullough

I was thinking about the water pump turning backwards too, but the pump came from a 1983 s-10. I believe you may be right about the timing chain cover though. I can't remember what year or model car it was used for. I would almost bet money thatís the problem. I had actually purchased two covers. The first one did no match the oil pan I had so I bought another one that bolts to the front of the oil pan. Is there anyway to tell which cover is the correct one?
Shawn Kennedy

The oil pan/front timing covers had two different shapes.

Early- used a 45 degree tilt to mate the two using a CORK gasket.

Late- used a rounded bottom pan with a rubber gasket connecting the two.

I assume you used a late style to use the modern gasket and the modern way of sealing the motor.. If this is the case, I have seen certain motors that ran the water pump backwards. Now, I am not sure how well the water pumps would fit, but what I have seen a few weeks back, they might interchange without noticing until overheating.... I did not look at this extremely close, but it was for another client who was using my backwards running waterpump setup off a 1993-95 Camaro 3.4L V6. vs. the early style motor front cover (actually a modern crate motor cover!) The two had the appearance of being able to be interchanged and it was pretty obvious that all the bolt holes were shared for both covers.

The only way to tell is to figure which way the motor turns, then pull the waterpump off and check the flow direction of the pump and cover... Make sure the other cover looks like it spins the water in the same direction.

Again, I do not know if the two waterpumps can be interchanged that easy, but close. I do have a crate motor front cover that was not used for a different motor so I could take a picture of it and email it too you for comparison.
Check to see if the water is circulating in the correct direction. See that it should be pulling from the bottom hose and flowing back out of the top hose at a very quick rate after the thermostat is open.

Otherwise take the sqaure pistons out of your motor and install round ones like the rest of us have. LOL!
BMC Brian McCullough


I believe Brian has you steered in the right direction. I found this info on a web search that may help.

<<1987 introduced the serpentine belt. This required the front cover to be machined to work with a water pump turning in the opposite direction from the crankshaft. The only visible difference between the front covers is the direction of the 'swirls' machined in the area behind the water pump impeller. This makes a difference in the coolant flow and an engine with the wrong front cover will have cooling problems. >>

This thread was discussed between 07/04/2003 and 09/04/2003

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