vents around spare tire

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  • #233884
    greg press
    Participant

    @greg-press

    I have read in this forumn that you should not put vynal spare tire cover over spare tire because it stops air from getting to the engine.The problem is i like my cover.[see my picture]I was thinking about cutting vents in fiberglass top and sides of engine hood and covering with fancy chrome plate.

    What do you people think?

    #248317
    newkitman
    Participant

    @newkitman

    The slots in the spare tire cover are really to let the hot air escape the engine compartment.
    As for the slots in the engine cover and covered with a chrome plate, the (VW based) Jaguar SS-100 kit car has those slots around the top of the engine cover on both sides and it looks pretty good. At least on the Jag SS-100. I think it may also be on the Mercedes Gazelle but not certain. Not ure how it would look on a TD though. One of those thing that make you go Hmm……..

    Allen Caron
    VW based 53MGTD - "MoneyPenny"
    "If one thing matters, everything matters" - from the book The Shack

    #248318
    Royal
    Participant

    @royal

    Is the thinking here that you need vents to improve ventilation to reduce vapor lock after a run on a hot day?  Or is it to improve cooling while running?  My MiGi has a factory fiberglass fake spare tire on the trunk.  I don’t think that it would look good, with vents in it.

    On MiGi, the whole back end swings up, even the valance.  Sure makes things easy to work on.  By removing a few screws that hold the engine cover on, I could even pull my engine out from the top with a chain fall and a tree limb capable of holding 256#.  If I removed the back bumper, I could tie a rope around MiGi’s nose and hoist her up a tree and 4 bolts and a couple of wires later, the engine would just fall out.  (Reminiscent of deer season in the Catskill Mountains.)

    I have not yet been through a summer with warm temps and hot roads.  MiGi and I are wondering what to expect.  I did install an oil temp gauge and I own an infrared thermometer.

    #248319
    edward ericson
    Participant

    @edsnova

    I wouldn’t start punching holes in anything before I knew if the thing would run hot.

    You have good tins? All of ’em? And sealed nice so all that hot stuff underneath where the exhaust runs is blocked from the top of the engine?

    If so, then check: is your carb sucking enough air to run the engine?

    If so, you’ve probably got enough topside ventilation.

    You might end up with a hot-running problem at some point. But if/when that happens, I’d re-check all the other stuff, plus make sure the fan intake isn’t blocked, etc., before I’d start drilling into the back deck ‘glass.

    Just FYI. On a TD, that hump in back is supposed to be the gas tank.

    #248320
    Paul Mossberg
    Keymaster

    @pmossberg

    I’m not questioning the VW gospel of sealing the engine compartment…but…

    All that gospel was written about stock, steel bodies VWs, where the hot little engine is sealed into a steel compartment.

    On a Migi, where the entire rear cover, valance included, swings up and out of the way, there is NOTHING to seal the engine cooling tin to. You can have all the proper tin in place, but the panels surrounding the engine have nothing to seal to.

    How much different is that than a dune buggy, with its engine hanging off the back? Granted our engines are not “out in the air”, but they are also not sealed into a steel box like a stock VW.

    In the VW based Classic Roadsters Ltd. Duchess, the engine cover is separate from the valance, but when you swing it back, there is no engine compartment floor so to speak. Hence there is no way I could seal the engine compartment and separate the upper and lower portions of the engine.

    I’ve run my Duchess since 1983 with the proper engine tin (so airflow is directed over the cylinder heads), but with no other separation of the upper part of the engine from the lower part and the exhaust.

    Hmmm…I guess I am questioning the VW cooling gospel!

    Thoughts?

     

    PMOSSBERG40898.5767476852

    Paul Mossberg
    Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
    2005 Intermeccanica Roadster

    If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)

    #248321
    Paul Mossberg
    Keymaster

    @pmossberg

    By the way, a simple diagram that illustrates what we are talking about:

    This also illustrates, to some degree, how tight a VW engine compartment is. I really think we get more general airflow around our engines.

    PMOSSBERG40898.4335069444

    Paul Mossberg
    Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
    2005 Intermeccanica Roadster

    If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)

    #248322
    Paul Mossberg
    Keymaster

    @pmossberg

    And on the question that stared this all, I don’t think cutting vents into the engine cover will do anything.

    The VW deck lid is not vented. The vents above the deck lid are intake vents for the cooling fan.

    If anything, I suspect that having vents along the top of the TD replica engine cover might (and I mean MIGHT) actually pull warmed air up from the exhaust and heads over the top end.

    I’m just speculating. Until one of us puts our car in a wind tunnel and is able to track air flow patterns around the back of the car, we will never really know.

    Paul Mossberg
    Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
    2005 Intermeccanica Roadster

    If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)

    #248323
    greg press
    Participant

    @greg-press

    Thank you every one .Because of all of you ownership of this car is alot easier 

    #248324
    Royal
    Participant

    @royal

    Thanks Paul.  I’m with you 100% on everything you said. 

    #248325
    Marc Lipsius
    Participant

    @mrlmd

    The vents in the rear deck over the engine are to let sufficient cooling air IN, so the fan can blow it over the oil cooler, not to let hot air OUT. If you don’t have the tin underneath the engine topsides, separating it from the hot cylinders and exhaust, you will be theoretically sucking warm/hot air into the fan and not allowing it to do it’s job. While it may operate OK while driving along at 60 mph without the tin, it will tend to overheat pretty fast when the car is sitting or going slow, especially in hot weather. Ask me how I know, plus this is all over the other VW forums and advice columns. The engine runs “much more better” with all the tin in place and even with a forward firewall if you can construct one. You need those vents in the rear deck lid, and if you cover the spare you have to make something else of sufficient area to allow enough cooling air to enter the engine compartment.

    #248326
    Paul Mossberg
    Keymaster

    @pmossberg

    I KNOW you are right mrlmd!

    In particular…the vents on the Beetle.

    But I suspect with the odd airflow that is going over our cars, we’re not pulling to much air in through the spare tire mount (if you have one) or vents cut into the deck lid.

    I keep thinkng about all those TD replicas on the road (or at least that were on the road). And I’m willing to bet NONE of them have a fully sealed engine compartment. OK, maybe a handful do. But not many!

    Some MiGi’s have a solid engine cover, with a molded in “tire” shape. Are they all blowing motors due to overheating?

    And what about dune buggies (on and off road). Thsoe engines are just hanging out there with nothing.

    And professional, high performance VW powered off road buggies…the kind that run the Baja 1000 and other off road dirt races. Cooling tin…YES. But again the engines are just hanging out there.

    They all buck the conventional approach!

    Given the “right way to do it”, I know they are wrong. All I’m saying is they still are not blowing engines left and right!

    PMOSSBERG40898.6969328704

    Paul Mossberg
    Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
    2005 Intermeccanica Roadster

    If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)

    #248327
    Royal
    Participant

    @royal

    So, to put this to rest (maybe), I conducted a small experiment:  I loosened the top hinge on my MiGi so that there was an obvious gap at the top.  With the engine running and fully warmed up, in my garage.  I could not get smoke held at the gap to go into the engine compartment.  In fact, it seemed to want to go out.  This may be due to the convection since the engine was warmed up and heating the air.  Conclusion is that Paul wins. 

    In the case of our TD replicas with no ability to separate the upper from the lower with engine tin, it appears that vents in the top won’t really do anything to keep a running engine cool.  This is why I wondered (above) if the reason for the proposed vents (not VW vents, but cutting new TD vents in the engine cover) was to speed cooling the engine down once it is turned off, – reducing the baking off of the fuel in the carburetor/fuel pump.  (You may be able to tell that all my Christmas shopping is done.)

    #248328
    edward ericson
    Participant

    @edsnova

    Paul’s point about the tins is absolutely correct and well taken.

    But there is sometimes trouble with these engines, I think, in these cars. Paul himself sucked a valve two years ago on the way to Carlisle. How many miles on that puppy? And was it abused? I’m betting heavily it was not.

    Most of these cars run so few miles, and the stock-type VW engines we usually have are so overbuilt, it’s very hard to say how much stress we’re putting on them with our tins/no tins setups.

    (For the record, the BCW has no “vents” in the rear deck, but some small gaps around the hinges. My engine has indeterminate mileage and is of indeterminate displacement–it’s an original, 1966-vintage 1300cc case with, I’m guessing, 1500 jugs and single port heads. The tins are all there, but the edges are not sealed and there in no firewall behind the fan shroud. No oil cooler, full-flow filter or any of that fancy stuff. I put about 4500 miles on it in the last two seasons and it seems to run just fine in all weather conditions–though it’s carbed waaay rich. Gotta fix that in the spring.) So far I’ve gone by the can-you-handle-the-dipstick rule of thumb and it’s never been too hot for that. I just installed a Gene Berg dipstick temp warning light at the end of last season and will be watching it very closely next year.

    Some of the Speedster guys are running cylinder head temp gauges but they mostly have 1915s and up, they run big cams and most of them do have their tins sealed in the factory way. So no good comparison there.

    But it does seem that many of them have engine troubles/per/mile ratios well beyond what I would find acceptable.

    Bottom line for us is, I think, try to keep an eye on it (or an infrared thermometer, CHT gauge, oil temp guage, etc. I propose we compare notes in July and see what everyone is doing and how it works.

    #248329
    Marc Lipsius
    Participant

    @mrlmd

    Dune buggies with totally exposed engines are not at all comparable to our cars. The tin keeps the hot air from going into the fan in our cars because we have a rear deck lid that can trap the hot gases. The fact that most of the TD’s have no tin separating upper and lower engine just shows how lucky those owners are that their cars don’t overheat and/or burn out the #3 cylinder which is the most common failure. The fact that most of the cars have no problem doesn’t mean that it’s right, it just means at least for the time being, you got away with it. All the reading on multiple sites and books that I’ve been on recommend all the tin be in place for these cars to maintain proper cooling. And if your car runs lean, it will be more prone to overheating. Running rich mitigates against that to some extent.

    #248330
    Paul Mossberg
    Keymaster

    @pmossberg

    Like I said….we all know the RIGHT way. But a lot of miles on a lot of VW based TD replicas without overheating problems has to be more than just luck. I’m just sayin….

    Bottom line, if you are able to seal off the upper from the lower engine…do it. But if you are unable to, due to the design of your car, I’m pretty convinced you won’t cause yourself a problem.

    Ed is right, I lost a valve. It was not on the #3 cylinder which is the one that normally overheats. And the reality is, I do not know what happened yet. As ya’ll know, the car is not, um, with me at the moment! So a tear down has not occurred.

    Paul Mossberg
    Former Owner of a 1981 Classic Roadsters Ltd. Duchess (VW)
    2005 Intermeccanica Roadster

    If you own a TDr and are not in the Registry, please go to https://tdreplica.com/forums/topic/mg-td-replica-registry/ and register (you need to copy and paste the link)

    #248331
    newkitman
    Participant

    @newkitman

    Paul….when you do get the TD back and start the teardown, if your engine does not have the doghouse style oil cooler that’d be a good time to switch. maybe even run an external oil cooler. Seriously thinking of that with mine. 

    Allen Caron
    VW based 53MGTD - "MoneyPenny"
    "If one thing matters, everything matters" - from the book The Shack

    #248332
    Paul Allain
    Participant

    @pga64

    Just my 2 cents. My TD has a fake tire cover, no vents. I’ve driven over 20,000 miles in the two years I’ve had it. In weather that was in the 80’s and 90’s to cold weather in the 30’s. I’ve never had a problem.

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