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MG MGB GT V8 Factory Originals Technical - Active venting of under-bonnet hot air?

I cannot keep my V8 cool in hot weather in stop-and-go driving. I just can't. Invested heavily in a super-ultra-heavy-duty, oversized rad core and installed a huge water pump fan + two electric pushers. Absolutely fine when moving. But it just goes up and up when parked in hot weather.

One idea I had is: is there any reason I couldn't drill a big hole in the bonnet (I was thinking about the LHS, say a few inches to the left of the fresh fair vent on the cowl, near the trailing edge of the bonnet) and install a 6" electric pusher fan (which I'd hook up to my thermostatically-controlled (200 degrees on) pushers in front of the rad? That could blast out trapped hot air, which I think is the only real problem, really effectively. I think by judicious use of stainless mesh one could do an attractive installation, and it shouldn't be too hard to build a tray out of sheet aluminum to guide rain water to an acceptable location. Any comments?
Fred Testa

With those fans you should have enough pressure to just push the air out. Be careful with vents near the windcreen as that's a high pressure area when you're moving. Try at least a third back. Check the archives on louvres as there's a lot about it.
Stuart Robson

Thanks Stuart. I was thinking about using the very rear of the bonnet for just this reason. When moving along, you'd turn the fan off and get some cold air forced in there, which is of course super carburetion-wise. When in stop-and-go traffic, you'd fire it up and purge that awful backlog of hot air!
Fred Testa

Fred

For comparison - the two pusher fans on the facory car will control engine water temperature someway short of boiling in S. European Summer temps (85 - 95 F) - as Stuart says if your arrangement doesn't cope the archives have a wealth of opinion mixed with fact. Perhaps you might also question why your car runs hotter than the factory car.

For all the solutions suggested in the past (and there are many) louvres in the bonnet, RV8 headers and coated or lagged block-huggers all have the desired effect of helping the engine run cooler but efficient fans and good oil circulation are still essential.

Roger

Are you sure you have sufficient water movement. Maybe a smaller water pump pulley would help?
Also the rad fans would work much better if they are ducted onto the rad. It is important to get a small clearance between the tip of the fan blades and the duct. You want the air to go through the rad so make sure it is ducted right up to the rad itself.
T Green

Fred,
The problem seems to be that the hot air can't get out when the car is stationary, if the temp drops to normal (as mine used to) after a few minutes of driving, this would confirm it.

Putting louvres facing backwards in the bonnet solved the problem for me, I offer it as a probable solution.

Mike
Michael barnfather

Michael, that's it exactly. No problem whatsoever once the car gets rolling. I hate to do the louver thing b/c of rain, but it just seems clear it's the best answer. And they look killer to boot.

How did E-type Jags get rid of rain water?

I took a look at the picture of your car on the V8 Register (a beauty, BTW) and my only question would be, wouldn't it be better to have the louvers up front closer to the radiator?
Fred Testa

Fred,
What exhaust are you using? RV8 style exhausts have those big holes in the inner fenders and when driving will help the car cool even more quickly. When I first got my conversion started I had the same problem as you, then I wrapped about the first 6" of my RV8 headers in heat wrap, and the under bonnet temperatures dropped significantly. I wish I had ceramic coated the headers before I started using them, because I've heard it doesn't work as well on used headers, so I haven't gone that route. What thermostat is in your car? Are you using any redline water wetter? My car will still push above 200ºF in the hottest of days and worst of traffic, but otherwise it typically stays below 200 all the time now.

Going on a little memory here, the formula I was given states that if you take the height of the windscreen and measure from the base of the screen forward onto the bonnet that length, that will tell you where the high pressure ends and low pressure areas begin. A low pressure area will suck air out while moving (i.e. wheel wells with the rv8 headers) I still may end up putting louvers in my bonnet, and if I do they'll be out of a 1993 pontiac grand prix gtp. Those to me were the closest shape and size I wanted without spending exorbitantly.

Where in Detroit are you?
Justin
Justin

Fred,
One thing is what do you consider hot weather. I am really concerned you are making changes and doing lots of work that is not curing some potential underlying problem. Case in point. I am running a Ford 302 V8, with a STOCK 25yrd old MGB radiator and stock pusher fans. Yes she gets warm on "hot" days here which means 85*F sitting in traffic, but she has not boiled yet. I do have a high volume water pump but will actually be dropping that soon as I am fairly certain it is cavitating at freeway cruise speeds. I will be converting to a serpentine belt system and a std flow water pump with smaller water pump pulley, then installing a 16" puller fan which should offset the loss of flow at idle.. Time will tell..

Larry Embrey

Larry, is your 302 completely stock? On my first warmed over 215 I tried to save some money by using the 4 cyl radiator 2 puller fans and it lasted about 10 minutes. Repaired it, used a stronger cap - lasted about 15 minutes before it blew up. This was not an original MGB radiator but a replacement, however.
My solution was to use a Ford radiator that is much taller than MGB radiator along with a 16" puller fan. Even in 100 degree days and brutal abuse at the drag strip it manages to stay cool. I do have large holes for the headers to pass through.
Fred, my suggestion is to first try to make your fans more effecient by making them pullers along with some kind of shroud, before you tear into that hood.
joaquin

Fred,

Thanks for the compliment.

we get A LOT of rain here, Just south of the Lake District, never had any problems. (It looks most impressive if I fire it up in public after a shower, loads of steam through the louvres(especially if I turn on the fan overide switch)).My exhausts are lagged with fibreglas tape all then way to the 'y' joint, and it does tend to hold water when parked in the rain.

The louvres are just above and behind the exhausts, on the only comparatively flat part of the bonnet, there really wasn't enough room forward of this, as the hump is in the way.

I does work very well, you can see the heat haze rising when in traffic queues !

Mike
Michael barnfather

Joaquin,
no it is not a stock 302. Mild cam, Alum heads full length headers, Edelbrock intake..
Larry Embrey

I am experiencing exactly the same overheating problems - ie fine while moving but temp shoots up when idling in traffic. The strange thing for me is that this has only just started to happen after fitting a new cam and new (unipart) water pump. The cam is fully bedded in so my only conclusion is that my water pump is less effective than my old (leaking) one, which doesn't seem right....
Chris Holmes

Chris, have you checked into having your old pump rebuilt? I would give that a look..
Larry Embrey

Fred,

If you want to test your active venting theory without cutting the car you could mount a squirrel cage type of fan as is used for the heater in a high location in the engine compartment and direct the output through the removable plug behind the glove box. I’m not suggesting this as a solution, just as a test. Fans like those used on radiators are best for moving air in a straight line, but squirrel cage fans are better pushing air through a duct. If this is wired to a switch you can control from the driver seat you can watch the temperature as you drive and stop and see the results when you turn it on.
George Champion

Fred - I do think Larry's concern is well-found - the engines will continue to operate seemingly very near to the red line and just so long as your fans don't pack up, you may not need to worry. You will of course eventually fry your electric string but that happens anyway

George's trial with an extractor through the plug in the firewall would demonstrate the effectivesness of finding somewhere for all that hot air to go. Working on the same principle, the holes cut (and strengthened)in my old girl allow the hot air to exit from the box sections in the top rear of the engine bay and vent into the front wing boxes - this clears some hot air but I suspect not as much as holes cut through the inner wings straight into the wheel arches. Whatever you do, the fans will need to run continuously. The fans are the key even louvres need the fans to be effective.
Roger

A couple of MGA bonnet/hood vents might not look so bad, if carefully placed.
Peter

Peter,

... good idea, but they do say "MGA" on 'em which is kinda wierd ...
Ted

Ted,
You can always tell people that this is because a V8 MG is "A" whole lot better than the average MG. Risky though, there is such a thing as justifiable Homoside.

Seriously though, you could always remove the MGA and graft on a MGB boot/trunk badge.
I'm starting to like the idea.
Peter

In addition to TR7 fan mounted on front of engine & original electric fans out front, I've modifyied my inner fenders to flow air out through them...I have RV-8 headers & smoothed the concave portion of the inner fenders in front of them so they act as ducts pulling into them from around sides of engine...plus, I've cut holes in 'trumpets' so that air can be pulled from rear upper part of inner fenders through trumpets & out vents I'm putting in fiberglass fenders...since I moved my fuze block back up under dash, I was able to cut a second rectangular hole in the passenger inner fender to match those in the driver inner fender.
anthony barnhill

This thread was discussed between 30/09/2002 and 11/10/2002

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