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MG MGB GT V8 Factory Originals Technical - Overheating MG V8

Iv'e decided to start a new thread for this as I sort of jumped onto someone else's before. thanks to all who contributed, keep thinking!

Background about car,

Southern California 77 MG V8 emissions legal (catilyst)fuel injected 3.5 liter 1980 SD1 with LT77 box and stock rear end.
I use RV8 type header and a large 4 core radiator with twin electric fans. overheats in any conditions above 80 degrees (about every day here)

OK, back to the story.

Still runs hot but blood letting into the street apears to be solved with relocation of expansion tank. I measured underhood temps at about 245 degrees. Is this to hot? Also it seems to not want to tranfer heat even at freeway speeds. So even with full cooling through radiator it is marginal. I'm beginning to think my water pump timing cover combination may be part of the problem by simply not circulating coolant. I have a 1980 SD1 3.5 block and front cover. has the water pump mounted low like original MG V8. I am using a 1963 Buick Short nose (AC)
water pump. It bolted right up to the front cover with no modification and all the same hose attachments, I assumed the clearance between the cover and pump would be good. Does anyone use the same combination of components with success? I did this because the SD1 pump was to small and the buick pump is very available in the US. Also is the Rover SD1 temp sender compatable with the MG temp gauge?

All the best,

Mark.
M Mallaby

Hi Mark,
First of all , the sender is not compatible, as I found out with an identical conversion. The temperature gauge will read in the red at about 75 degrees C when used with the SDI transmitter. Use the one from the 4 cylinder MGB engine unit which will fit the V8 manifold and is resistance matched to the gauge. On my car the needle reads vertical in between the two calibration dots at 90 deg C , which is about the point at which the fans cut in on a themostatic switch installed in the upper radiator tank.
I would also recommend checking the actual outlet temp from the engine with a laser temperature gun to ensure that you are happy with the reading that the gauge is displaying.
I used an MGBV8 water pump with a 4 core radiator much longer than standard( down to the cross member), twin MGBV8 fans and RV8 exhaust system. No overheating problems, although the fans run a lot in traffic.

Regards,
Tony.
TONY FREW

Mark,

the pump you selected is ok for a SD1 engine, the temp. sender might be an other theme.
I got rid of this electric control and changed to a mechanic temp. control/oil pressure instrument.
During normal crusing on the freeway, it reads between 80 and 85 deg. cent., using a 78 deg. cent. thermostat and a kenlow switch set to 82 deg. cent.
The fans are not cut of by the ignition systen so they run on after the engine is stopped, avoiding the temperature rises when parking the car.
During stop and go in the city, the temp. rises up to 95 deg. even with the heater switched on.
Rover quoted it would be best to stay below 90 deg. as the engine looses power beyond this temperature.

Althoug my car is fitted with a Holley 390, I also run RV8 style headers and twin electric fans behind the normal V8 radiator that is fitted without the normal mounts, adding ventilation to the headers.
The expansion tank has a 15 PSI cap and is mouted very close to the radiator.

Have you checked that there are no air locks in the system (leaky heater valves have been common to my V8 until I changed the valve to a in line version from an old AUDI.
Which thermastat is on the engine and does it work? There are three differnt ones quoted in the Rover manuals, depending upon export destination of the car the engine came from.
When changing engine oil, do not trust the marks on the dip stick, most MGB V8 conversions are running low oil levels although the reading is 'HIGH'... this can also boost the temperature of the engine!

Has an exhaust gas analysis been made? Is everything O.K. with the airflow meter and can it suck fresh air from an air cleaner in front of the radiator?

Are timing and sparks ok? Take care with the Lucas Opus electronic distributer, two of the electronic boards inside the dizzy failed in my car when getting too hot and I changed to a Piranha/Newtronic system some years ago.

Another point to check is the 3.9 rear axle. It does not help to keep the temperature within the limits.
O.K., it helps to have wheelspinn even in 4th. gear and is fun to drive ... sometimes, but high engine speeds allways mean high temperatures underneath the bonnet.
If there is a chance to pick a 3.3 or 3.09 from a MGC, you shold not wait for another occasion to come!

Ralph

Ralph

Ahh so maybe I'm not over heating at all! Would like to switch to 3.08 gears sometime in the future. Thanks for the conformation on the water pump, would be a bummer to have to re-engineer the pulley system. I've ordered a new MGB 4 cyl temp sender (gave away the old one with the old motor) so We'll see how that goes.

thanks so much.
M Mallaby

Mark,

I have almost the identical set-up you do, '77 SD1 3.5 EFI. On occasion we also purged coolant on PCH in stop-and-go traffic.

I have solved the problem by installing a 16# cap (was 7#) and, more importantly, machining an aluminum piece to put in the highest part of the top radiator hose. This part has a 1/8 NPT plug that allows me to be sure that _all_ the air has been purged from the system.

I have a fitting on the intake manifold for this purpose, but it is lower than the top of the upper hose and I was never confident I was able to get all the air out of the system.

If you'd like a pic and pdf drawing, let me know.

Edd
Edd Weninger


"machining an aluminum piece to put in the highest part of the top radiator hose"

something like this, perhaps?
http://www.britishv8.org/MG/RobertMilks/RobertMilks-E.jpg

here's another example:
http://www.britishv8.org/MG/JohnMangles/JohnMangles-D.JPG
Curtis

Edd & Curtis, thanks for your thoughts.

I have been thinking of adding a purge hole in the top hose, sounds like I should. I have added a huge amount of additional ducting into the radiator last weekend. But to no real help. I completly flushed the engine block, drilled two 1/8th holes in the thermostat to aid air removal and fabricated an air box to draw only cool air from in front of the slam panel. I also checked my gauge and unfortunatly it reads correct. I put a thermocouple in the top hose and drove around for a while. I just kept creeping up to about 218 degrees F. All my work has slowed the speed of heat accumulation but not stopped it. I'm thinking I may now have a blown head gasket as a result of the overheating that is adding to (or be the cause) of the problem... I am going to rent a radiator pressure tester and see if coolant leaks into the bores before I yank the heads.

Wish me luck.



M Mallaby

I had the same problem with the apparent temp' when I attached my 3.9 manifold sender to the MG guage. Then I realized what was going on. I put a small variable resistor on the wire and adjusted it so that the temperature guage read "N" when the electric thermostat switched on the fan.

Just a thought, are you fans rotating in the right direction? Not as silly as it sounds, with so much air moving around it's hard to tell. I wired mine up backwrds initially and didn't realize for a while. Had to use a shread of tissue to tell.
Peter

What type of headers do you have? I have hugger headers on my V8. After cutting holes in the fender wells to allow heat to escape there was a noticeable difference in engine temps. The wheel wells have low air pressure which allows the heat to easily vent out of the engine compartment. This also allows more air to pass through the radiator resulting in better cooling. FWIW

brdave
BR Dave

If the 218F in the top hose is all you see, you might be OK. My everyday car '94 Cad ETC runs about that normally. If I were you I'd make sure all the air was out of the system, that led to my solution for the PCH gurgle, and do some more testing with the thermocouple.

245F underhood temp sounds a bit high. Do you have vents in the inner wings? My set-up has coated (inside and out) blockhuggers and has vented inner wings. No electric fans on mine.

Good Luck !!

Edd Weninger

I installed a remote filler at the highest point of the system, it helped my overheating problems along with the S/T air dam which ducts air through the oil cooler and lower part of the radiator really well. At freeway speeds and 100ºF (I'm in Sacramento), my temp stays around 195º without any fans. At stop lights my stock dual fans will push the temp down to that when it goes above 210º. I am running block hugger headers, Buick 300 waterpump on Rover 3.5 timing cover and Buick 215 engine with HIF6 carbs. Stock late MGB radiator.
http://i11.photobucket.com/albums/a154/filospinato/P3110617.jpg
Good luck.
Jake Voelckers

By jove, I think we've got it!

Last night I fabricated and installed the top hose bleeder valve, filled the system with 60/40 water / cooant, added water wetter, pressureized and bled the system. I was amazed at the amount of air trapped in the system. After letting her heat up and re-bleeding the system (more air)the fan came on (set to 180 deg)ran for a while and shut off. This is the first time scince the conversion that the cooling system has recovered itself at idle. 9:00pm went for a drive to the coast the car ran cooler and better than ever before. I now have a 7 lb cap on the main radiator and a 15 lb on the expansion tank now without the "PCH gurgle".

To all who have helped, thanks so much. Now I can enjoy the car and do some wineries this Fall (my wife will be pleased).

It's tough to say if it was one single thing or the combination of many but air in system, bad. Huge amounts of cowling and cold air induction, good.

thanks again, I'll bug you guys again at the next development hurdle.

Are these cars ever finished?

Mark.
M Mallaby

Mark,
RE: "I now have a 7 lb cap on the main radiator and a 15 lb on the expansion tank....."
If you have a true expansion (aka overflow/recovery) tank, this is a non pressurized vessel and it does not require a pressure cap. You cannot use it for initial cooling system fill.
If it is a surge tank (a pressurized vessel which is used for initial cooling system fill), then it should have a pressure cap.
Might want to review your plumbing and if done correctly, the cooling system should only need one pressure cap (in your case, 15lb is OK).
Graham Creswick

This thread was discussed between 29/08/2006 and 12/09/2006

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