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MG MGB GT V8 Factory Originals Technical - Bonnet seal removal ... a good call!

If I recall, it was Chris Betson who advocated pulling off the rear hood (bonnet) seal to increase venting of the engine bay. Before I drove the V8 to work this AM, I popped the hood and just for kicks pulled off that seal. My commute today was about an hour; the first half was on the highway and the second half was stop-and-go. The thing that blows me away is how cool the car ran on the highway -- well _below_ N (no, the sender's not malfunctioning; I drive the car most every day) ... the needle was halfway between N and the hashmark to the left of it. First time I've ever seen that; I did a double take for sure. In traffic, the needle hovered ever so slightly above N. The secondary fans, which come on at 200 deg F, never once turned on. Of course, ambient temp was only 68 deg F this AM, but still.

As indicated in the other thread, I seem to have pretty much licked the cooling issue, but Chris's method saves you an additional ten degrees or so ... and it seems to obviate the need altogether for things like hood vents, with their attendant rain and aesthetic issues. Sometimes the best solutions are the simplest. I'm not sure why the hood seal is there to begin with, other than possibly reducing the noise level (which is a lost cause in this case).
David

Yup, it was me 8-)......

I think the intention of the seal is to stop any oil smoke that may come from the engine getting up onto the windscreen - but, since this is a high pressure area at speed - the airflow should actually be INTO the engine compartment!

At low speed or stationary, the fan(s) should blow air through the rad and this hot air will escape from all round the rear of the hood (bonnet) as well as by natural convection.

I also do not have the soundproofing felt under my bonnet (hood) which also helps with heat radiation.....
Chris Betson

Sounds like an interesting way of doing things.. I'll have to take a look and see how much one of our fans would push air through there at idle for couriosity sake.
I believe that the seal may also be there for hood shake, or the lack thereof. You may notice on the MG as well as most cars, that a seal exists and when removed, the hood will have a little more shake due to vibration or wind. One of my Non-MG vehicles has this seal out and it shakes like you wouldn't believe at speeds over the posted limit. I think a good compromise to this would be to take and cut two four inch pieces to your factory seal and place them behind the hinge area if you find the hood (Bonnet) to shake excessively.

Chris and Dave,
Have you noticed any additional hood shakeor vibration at idle, road speed or above posted speed limits? Not that you guys would do that :-)
BMC Brian McCullough

Brian, you're totally right ... unfortunately the holddown bolt for the air cleaner dented the hood for exactly this reason. Aargh, I just had the whole thing repainted last summer!
David

I just cut the seal in half & slid both pieces around to the front of the car until they touched the bonnet/hood stops. This gives a 24" gap between the seals at the rear of the engine bay. I have checked it out by running the fans & feeling for airflow. I've thought about bending the rim down slightly at this point to further the airflow.
Barrie E
Barrie Egerton

Brian,

No I have not noticed any bonnet (hood) shake at all. At idle, normal speeds or around 130 mph........ (V8)

But if you are concerned, then why not fit a couple of the buffers fitted in the channel of the wings at the front to the rear part of the channels?
Chris Betson

Guys, the Bonnet seal stops your feet getting wet. I removed it because I'd heard of the cooling effect. My enthusiam for the cooling benefits was significantly dampend the first time it rained heavily. Its amazing just how much water an MG can collect and conduct down onto your feet via the pedal Box. Since my car is a LHD RHD conversion the rest of the footwells were also a bit colander like. Dilegent application of silicon sealant didn't fix the problem, infact fixing leaks elswhere increased the flow directly above my feet. Not one to give up lightly I build up a sort of small silicon dam around the pedal box. The waterfall then shifted to above the accellerator pedal. Siliconing there shifted the leak to the heater and which after being given the silicon treatment caused the leak to return to its natural home, the pedal box directly above my feet. At that point I gave up and put the seal back.

For those of you with cooling problems I've heard that cutting holes in your guards (RV8 style) is said to do wonders. The wheels are a low pressure region.
Peter

Australian rain must have unique qualities - good old British rain doesn't seem to be able to fight its way into the engine compartment, let alone into my footwells......8-)

Chris Betson

Chris
It is, of couse, AUSTRALIAN rain and therefore much more powerful than other varieties.
Peter

Peter - the RV8 cutaway in the inner wing does seem to do the trick although the engine bay is still very hot at the top. The disadvantage apparently is additional noise at high speed and un-answered questions about strength.

Going back to the main thread - one of the TVRs has vents in the sides of the bonnet and there ought to be scope for getting a lot of hot air out of a B engine bay in this way.

Mine vents into the box section of the wing behind the splashguards. Works so long as the fans are on. (But they all overheat without the fans)

Roger
Roger

Roger,
Smart idea re: box section venting. Unobtrusive and nice and high up. May I ask how large a hole did you make, or did you drill lots of small holes ? Have you removed the entire spash guard or just the top?. Would this still work as effectivly with RV8 style headers generating lots of heat in the wheel arches do you think?.
Peter

If any of the more difficult bolts around the pedal box are left out then any rain that gets past the seal (if you still have one) can find itself onto your feet. I have recently been accused of ruining the character of someones MGB by stopping just such a leak.
Paul Hunt

Hello all, I am able to comment on this tread now with the question on some peoples minds about louvers and rain. I drove my 22 louvered B in pouring rain at night and no wipers, when i got home i noticed a dry area around the perimeter of the louvers, when the rest of the hood was wet (i was able to see this beacause the hood is only primered at this point) lifted the hood and the engine compartment was also dry. well, it seems to me that at least at speed the heat comming out from the louvers blows the water away.
Romney
Romney

Read about it here and then pulled the seal. I just put my Rover 3.5 back on the road for the driving season here in Vancouver, so far no bonnet shaking, And it’s still a little cool here to comment much on any reduction in temperature. I did do the modification to the heater valve as outlined by Bob and that seems to working quite well. I am planning on a couple of trip’s up to British Columbia’s interior this summer where the temps run in the high 30’s C (92 F) and higher, so will post a msg then with regards to lower engine temps re the bonnet seal. Keep the great simple ideas coming.


Bruce
Bruce

A simple solution, if anyone dares, is to cut 12" from the lip at the rear of the fender to both sides, living about a 1/4" lip and do the same to the hood. This will create an invisible vent that will expel hot air from the engine bay. I have done this on hihgly modified non-MG cars and some MG's.
It may leak some water, if any, onto the engine bay on the exhaust side if you live in Australia. In other parts of the world it may work just right if you dare to cut metal from your MG.
Yes Brian by removing the hood seal the hood will shake at Fwy speeds, specially in a cross wind and it's a great idea to place a buffer on the hood.
It's a great idea to removed the seal, if you don't experience Australian rain. :-)
Bill Guzman

This thread was discussed between 10/04/2002 and 21/04/2002

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