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MG MGB GT V8 Factory Originals Technical - Cooling woes
|Well sort of, the only time my V8 conversion overheats is sitting in slow traffic on a hot day. Ford 302 with a Stewart Stage 1 HD water pump, fresh coolant with waterwetter, a large Griffin crossflow rad and a 16" Permacool 3600 cfm electric cooling fan and I have made sure there are no air pockets.There is only two more things I can think to do and would like to hear if you guys think either would be worth trying.|
Adding a second 16" 3600cfm cooling fan infront as a pusher in addition to the puller I now have and installing smaller dia. water pump pulley so that the coolant would circulate faster at idle.
Do either of those sound like they might work?
First you need to determine if it's a coolant flow problem or an air flow problem. I suspect it's a coolant flow problem, but here's how to find out.
Next time you're sitting in traffic, keep the engine revs up to around 2000 or so and see what happens. This will increase your coolant flow but will have no impact on the air flow. If the engine stays cool when you do this, then it's a coolant flow problem; if not, then it's an air flow problem.
I had this problem with my stock TR6, and it turned out to be a faulty water pump. Even though it was a brand new unit, the impellor blades were slightly tapered, allowing water to bypass the blades at low engine speeds. Almost imperceptable to the eye, but a new pump cured the problem.
I don't think a second fan would help if it's an air flow problem. The first fan should be able to provide sufficient air flow "into" the engine bay. The problem, if it's air flow, most likely would be getting air flow "out-of" the engine bay.
|Chris, how high is the top of your radiator in relation to the engine? If it is lower than the water jackets in the heads you may need a surge tank to make sure you aren't getting air pockets in the water jackets.|
|The rpm test could also show the other side of the coolant flow issue. you CAN move the coolant to fast/ cavitate the pump. I had lots of problems with my old set-up using a high flow water pump in a stock rad.. |
THe car would get really hot when rpm got much over 3k, the pump was either cavitating or moving coolant so fast that the rad could not pull the heat out fast enough... Stock type water pump now and not cooling issues regardless of RPM....
yeah 3600cfm is a HUGE amount of air, if that is not enough, you have other issues going on. I have 2 generic 8" fans on my 302 and while our temps are not as bad, I actually had problems with her getting cold due to a therm stuck open....
|When I did my Rover 3.5 conversion with a 3000CFM puller fan, Ford Falcon rad, I too had over heating problems here on BC's high mountain passes.|
I added ductwork, to force the air through the ST Front spoiler and the bottom of the rad, that helped but didnít cure the problem.
For me, installing louvers in the engine bay high up on the inner fenders did the trick.
With the V8, you got to get all the hot air out.
Jim the rad is 4" above the heads.
Dan, that sounds like a good test, I'll try it.
I should have added that I use 180F thermostat and 230F
is when I say too much and shut it down. Also I always pop the hood in traffic so there is a 2" gap at the back of the hood for hot air to escape (Triumph),
as well as wheel well holes right next to the headers.
Do you think adding an oil cooler would help?
| Bruce's comment on the addition of hood louvres to eliminate hot air has the additional benefit of lowering underhood pressure which translates into decreased system resistance for higher fan performance. A lot of cooling issues are the result of poor air flow through the core - venting of the engine bay is one way to promote better air flow. Fan suppliers extoll the performance virtues of their fans but CFM values drop off significantly when system resistance increases.|
Another way to improve airflow distribution across the core, that has been mentioned many times in the archives, is to add a well designed shroud to pull air through the corners of the rad. A well designed shroud should allow the fan to have about a 1/3 penetration into the shroud -too much fan immersion will promote air recirculation within the shroud from the fan radial air component. Most (electric) fans mount with an annular ring and do not pull (or push, in some cases) air through the entire core, only an annular "donut" shape is achieved. They also do not pull/push any air through the centre of the core since they are close mounted to the core and have the added restriction of the motor. If we had space in our conversions to allow more fan to core clearance, that (along with a shroud) would be a major benefit. A desirable fan to core clearance is 2x blade pitch width or greater.
I am also a strong supporter of the addition of recirc seals to prevent hot air from re-entering the core at an idle condition. Keep in mind that pressurized engine bay air is going to find the easiest escape route and if that is forward and around the rad, then there is a recirc problem that translates into worse cooling.
Chris, along with comments made from Dan, Jim et al, I would also discourage the use of an additional "pusher" fan. I believe that a better direction would be to focus on shroud and recirc issues.
|Even here in the UK we hit problems with heat when stuck in traffic.|
I'm convinced that it's not a radiator problem, but one of trapped heat, as the temp very soon returns to normal when I get underway.
I've fitted louvres towards the back of the bonnet, with small fans from a computer store behind them wired in with the rad fan. I've also raised the centre of the bonnet, and made a gap between the rear of the bonnet and the scuttle, it's maybe 10" long and 1/2" high.
When the fans come on you can see a tremendous heat haze rise, and the needle now no longer goes off the clock........we're off to France this summer, that will be the acid test.
|"but one of trapped heat"|
Easily checked, as the problem only seems to occur idling on a hot day lift the bonnet and see what happens.
|I am of the "trapped heat " opinion too. I had this recurring problem in traffic or stopped. Lack of air flow seemed the cause because I could run on highway with no fans running. the minute I added louvers on the rear of hood it really made a big difference. So this winter I have extended the louvered area and feel this should totally cure this over heating in traffic.I have also eliminated my 3 fans --2 puller 1 pusher --to a 14 " high volume pusher--no room for a big puller.|
MGB --302 V8
I agree on vents - where is the best location?
BMW specify to not use mineral oil if sump temp is over 130c and I would use a cooler if over 100c.
I live on Canada's west coast and it can get pretty wet here.
So instead of putting my louvers in the bonnet and risk having the engine being soaked for days on end, I cut out part of the inner fender in the engine bay. If you look up high and towards the back of the engine bay on the inner fender (both sides) is a flat spot.. I had some 5" louvers pressed into a couple of piece's of sheet metal and then fiber-glassed the louvers into place.
End of heating problem.
|Hi Bruce, good to see that you are surviving the winter on the Sunshine Coast. I'll be out your way in late April for a few days and may have time to look you up. Did you get your Fiero seats installed?|
I did something similar to what Bruce describes with his inner fenders. I used the already pressed louvers from some scrappped metal locker doors and welded them in place.
I've got an RV8 bonnet, so not a lot of choice, they just fit on the flat bits each side of the 'hump' just in front of the rear bonnet strengthener.
There are some pics on the X power forum (xpower-mg.com) gallery under mikeb.
|Take a look at http://www.performancebritish.com |
picture #46 of there GT restoration. they have put a piece of 3" or 4" exhaust pipe through the wheel well.
The say it works well, nice people
I did the test, it wasn't a hot day but I was sure I could get the temp. up there.
With the hood closed, fan off I let the temp. get up to
210F at idle then with hood closed turned on the fan, over the next 4 min. came down to 200F and stayed there.
Then with hood closed and fan off let temp. come back up to 210F then opened hood and turned on fan, same as the first time it took 4 min. to come down to 200F and stay there.
Closed the hood , turned off the fan let it come back up to 210F kept the hood closed turned on the fan and brought the revs up to 2000rpm and the temp. dropped
to 190F in about 30 seconds and stayed there as long as the revs were kept at 2000. I did the same test again, temp. at 210F, revs at 2000, fan on and opened the hood and again the temp.dropped to 190F
in about 30 sec. Since every bit of air is funneled
through the rad and there are large air vents right next to the headers and a 2inch by 4foot vent at the back of the hood I'm pretty sure air flow isn't a problem but a coolant flow problem.
So my first impulse is to mount a smaller dia.water
pump pulley to bring the waterpump speed up when at idle except for Larrys warning above. The only difference might be Larry you had a stock rad in there
that could handle the high volume your pump was giving and I'm using a huge crossflow alum. rad that was designed for a stock car. I think I know what I should do but I really respect the experience of this forum and a appreciate any other advice from you guys.
This thread was discussed between 03/03/2005 and 06/03/2005
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