Hi all, I find myself wondering if it would help to keep the under bonnet temperature down by removing the stone guards from the front on the car? With them in place, things are pretty well sealed up. I’m thinking that maybe with them removed the air would flow down and under the car. I realize that for aerodynamic purposes that it’s better to keep them in place. But I’m not going that fast. And the extra air flow, which would reduce the bonnet temp, would be welcomed if it actually worked that way. Has anyone done this?
Bob,
I just installed mine after 5 years without them. I noted lots of road debris under the bonnet without them. I never felt my engine temps were high so I can’t say if it will be better or worse, but I will watch that and report back if you like.
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I think that if you have overheating problems it wont matter whether they are in place or not. I guess you might argue that with the underside “sealed up” with the guards that airflow would be stronger through the radiator…also, I’ve always felt the front go light at speeds around 90, this was with the guards removed. Perhaps with the guards in place front end lift would be reduced. I’ll find out whne my car gets back on the road, with guards in place.
I beleive Pete Crespin once said that Jaguar never put anything on the car that they didn’t consider necessary. And remember, this is a very fast car so perhaps Jaguar tried it both ways and the guards was their cure for any lift.
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I agree with Peter, but necessary for what? Trying to maintain their reputation for 150 mph? High speed motoring will benefit from a smooth underbelly, which reduces turbulence and possibly lift. For a car driven a max of 80mph or so, it becomes less necessary. And reducing radiant temperatures both under the bonnet and inside the car becomes the priority?
I’m not claiming this is the case, but am wondering if if might help…
“…I’m not claiming this is the case, but am wondering if if might help……”
My car had overheating problems when I was running without the guards in place. It didn’t appear to have anything to do with the overheating problem because when I removed the radiator, had it cleaned out, fitted a new stat, overheating problem gone…oh and fitted a new otter switch.
Now this doesn’t determine whether or not the shields help, but it does suggest that not having the shields didn’t help my the overheating problem. The lift at high speed did make me nervous and in fact thought long and hard about fitting a small air dam on the front (at the suggestion of another lister that had the same problem), but I haven’t, yet, so am anxious to see what if anything having the shields being in place does to negate the issue.
With the caveat that I don’t know for sure, I suspect removing the shields might actually have the opposite effect from what you’re seeking. With shields, at speed the airflow path will be primarily through the grill and radiator, sweep past the engine, and go out through the bonnet louvers, with a fairly significant forced flow rate past the manifolds evacuating heat.
With the shields off, at speed the airflow passes through the radiator and then will be divided with some of it going out through the louvers but probably most of it exiting out from under the car since that that opening would have greater surface area. There would be less airflow past the manifolds, the area where it is needed the most to reduce the under-bonnet ambient temperatures. The cooling air flow past the exhaust manifolds will be more relying on just the pull from a lower pressure area above the bonnet and be more of a convection current rather than a much stronger forced air flow coming through the nose.
At a standstill with no fan running, the flow will naturally rise out the louvers but the flow rate will just be the convection current and there is plenty of areas where the fresh air is brought up from the bottom, so with or without shields wouldn’t make a difference.
As speed increases the front of an E-Type rises, indicating that air passing under the car pushes it up, ie it is a high pressure area. Above the bonnet is a low pressure area, that’s why the louvres are there. Surely removing the shields will allow some of that high pressure to equalise through the engine bay, potentially reducing the ability of the louvres to remove warmed air from the radiator? Maybe that’s why the shields were there?
It’s not obvious what the airflow situation will be at different roadspeeds. either with or without the shields.
They will protect components and the front of the lower bulkhead from debris.
The six cylinder car has lots of space under the bonnet by comparison with the twelve cylinder car and the v12s still have these shields…
There is no cooling problem when at high speed when plenty of water is circulating.
Cooling is primarily achieved by the extraction of hot water from the cylinder heads to the radiator, not by convection around the block. That means that a correctly working thermostat will set a floor to the temperature and increasing airflow will not change that.
Cooling capacity in poorly maintained cars is marginal when airflow and waterflow are at a minimum, so my suggestion would be to force the radiator fan to be on when running in stationary traffic and make sure the airflow cannot get around the fan, but be forced to go through the radiator. That’s what the radiator foam is for.
The only situation where removing them seems to be sensible is for a hot, stationary car (i.e. post shutdown) where the bonnet is kept closed.
More sensible would be to install an auxillary fan and force air extraction when under-bonnet temperature exceeds approximately 65’c, but even then, the thermostat “designs away” all excess cooling by maintaining the minimum temperature.
kind regards
Marek
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My (Texas) S1 has an AC kit. While the oversized radiator and the Coolcat fan (with shroud) keep engine coolant temps under control on 100*F days, the underbonnet temps soar when at a standstill. Carb tuning degrades and impacts idle. This is a known problem even without an AC.
I have removed the bonnet to cowl seal to allow a tiny extra bit of the hot air to escape through the crack. Next step is fabrication of a new left side heater duct/end cap to direct ambient outside air toward the alternator, compressor, and exhaust manifolds instead of the through the heater inlet. The last thing I need is a heater. A thermostatically controlled fan will be situated inside the duct. The next step will be a fan in the right side duct.
The purpose of the foam around the radiator is to make sure that all of the air goes through the radiator, so cooling via waterflow is maximised. Having a gap means that the air which comes in through the nose has a less restricted and easier route than passing through the radiator, so the little you may gain by air cooling the block is more than offset by what you lose by not water cooling the heads.
When the car is stationary or very slow moving, running the fan will be helpful as it’ll keep the air moving.
You are 100% wrong about the heater. The heater is much more useful than you think as it is in effect a mini-radiator which will help drop the water temperature further. What you really want is to run the heater on max when you are overheating but direct the unwanted hot air out of the cabin.
kind regards
Marek
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Two observations:
If you force air under a wing you aid lift. In my mind, that’s one in favor for the shields. My car starts dancing at 90, scary over the ton. No tins.
Second, as said, no tins in place or sealing foam on the radiator. My (S2) has never overheated, gauge needle on N in normal, and rises with ambient temps of 90F deg, or in traffic.
My block & head cooling passages are very clean, as is the rad. I suspect other measures (foam & air path) are secondary to the “basics” above.
That’s why Tweety sat nose-low: it was pretty stable, up to ~120. On the track, it had the small spoiler at the trailing edge of the lower surface of the bonnet, which further cut lift.
I’m speaking of the rubber seal at the aft end of the bonnet, not the foam/felt at the radiator end. The latter is new and undisturbed. Again, the objective in my case is to allow hot air to escape the engine compartment and/or to lower the under bonnet temperatures via injection of cooler ambient air when the vehicle is not moving.
I understand that the heater can serve as an auxiliary engine cooler…it’s an age old standby in the American southwest. But my issue is not engine coolant temperature…it’s engine compartment temperature, which builds rapidly at a standstill and disrupts carburetor function. Again, the radiator and fan are doing their job…but compartment temperatures rise rapidly without the extraction effect from the louvers in the bonnet (at a standstill).