Vents for Bonnet on 4x4
 

Hi All

Has anyone fitted vents to the bonnet of their 4x4 to allow the heat to escape, as my vehicle was getting way too hot on my last trip. The engine compartment has hardly any room for the heat to disperse and I'm not sure but just upgrading the fan etc will help the problem.

I have seen many versions of vents for the bonnet but I'm not sure what the effect would be with them taking in sand/water etc.

There is also a heat extractor that removes the heat from the engine compartment but it looks gross and may be just another thing that can fail?

Anyone got any advice/opinions which is the best way to go?

Thanks

Julio

my old 3.9 V8 90 used to run quite hot, what i did to help, was, on the front of the bonnet where the rubber pads are that "rest" on top of the radiator frame, i screwed on a couple more onto each pad, so that the front of the bonnet was slightly raised (about 1/2" or so).
it was hardly noticible to the naked eye (unless you "know" landrovers and could tell that the bonnet wasn't fully "down").
it got some extra air into there and helped things a bit.

what some folk also do (which, in association with raising the fronr of the bonnet would help a lot) is to cut some holes (about 1 1/2" diameter) at the back of the bonnet, just up from where it rests on the wing, near the windscreen/bulkhead, then rivet/glue/fix some mesh/gauze behind the holes to keep fingers out/engine in, about 3 or 4 on each side are what the comp-safari type vehicles seem to have.

Hi, Jim
You've done it, I haven't. So I'm just a bit nervous about adding my two pennyworth, but here goes: the primary method of cooling the engine is via its radiator, air is forced through the radiator into the engine compartment by the forward motion of the vehicle and/or by the fan. If you allow extra air into the engine compartment by opening the bonnet like you say then you will create a back pressure which will reduce the amount of air passing through the radiator. Granted, this additional air will dilute the hot air in the engine compartment, but I suspect the greatest improvement will be by providing additional exit vents WITHOUT opening the bonnet thereby reducing underbonnet pressure and allowing an increased flow thgrough the radiator. Does that make sense?
Cheers
John

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Johnefyn

Hi Julio,

I've always been a fan of Homer Simpson's "speed holes" concept, which might also work to reduce heat: grab a pick-axe and start swinging...

But a more serious option might be to add a air/hood scoop. Most of the turbo diesels around here have them for the intercoolers, but I imagine they'd work just as well to increase air circulation around a non-turbo engine.

Well mounted and screened it would keep everything but air out and certainly let out excess heat. Plus you can pick up a used one and install if yourself...a nice weekend project.

The point about reducing airflow through the radiator is a possibility...but I doubt it. Many engines have intercooler hood scoops with no additional radiator of venting modifications.

However since my inferior Isuzu doesn't seem to suffer from such a malady, I'll defer to those on this board who have experience with such things.... ;-)

--
GL
www.greenlaner.net

You could reverse fit a fan with a manual switch in front of the radiator. The guys I knew who tried thi it made a significant difference.(makes a push me pull me effect) Other option is a bigger rad or oil cooler if you have the space. It may be necessary to move the front panel forwards slightly to accomodate an extra fan but it is possible. On a landrover it is probably possible using LR parts as half the pulse ambulances for the army have had their front pannels moved forwards to accomodate extra kit.

My 3L TD Toyota 4Runner used to overheat like hell so I moved the spots from the bullbar to the roof to aid airflow (as they seemed to be blocking the rad). This wasn't enough so I had the rad pulled out and re-built from 3 core to 5 core - nearly doubling the coolant volume. Due to the extra depth of the rad I had to lose the viscous coupling and basicly hard wired the fan to the engine so that it runs all the time...a bit rad but no more overheating problems.

Jeremy,

Are you sure the problem was caused by the spots blocking air flow? I have two 24cm dia Lightforce lamps on the front bumper and never noticed the difference. Overheating in your case must have been caused by somethig else. Did you check the cooling system , e.g. cooling channels in the engine block? Also, did you check exhaust gas temperature to make sure the combustion wasn't too hot?

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Roman (UK)
www.overlandcruiser.info

Moving the spots aided the free flow of air across the rad as I had two big rectangular IPF 8 or 900s and this was OK for when I was towing a caravan etc but for African conditions I headed the advice of people who had the same problem with the same vehicle in Zimbabwe. I didn't check the cooling channels or the exhaust gas temperature although I fail to see how you can adjust the latter. Any further info on that subject would be appreciated.

Jeremy,

High exhaust gas temperature is the result of partial combustion, where fuel is still being burnt on it's way out of the the chambers. And the engine doesn't have to smoke to do that. When it hapens, the temperature may rise to a point (above 1700 deg F) where thermal damage to the valves will occur. It is generally accepted that max safe limit is 1250ºF. To give you a rough idea: my Toyota 1HD-T (4.2 turbodiesel) runs most of the time between 600 - 900 deg F. When towing uphill or at full trottle it goes up to 1100 - 1200 deg F. High EGT is usually caused by a clogged air filter, bad injectors or timing.

Hope it helps,

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Roman (UK)
www.overlandcruiser.info

What piece of kit do you use to measure this temp?

Jeremy,

I use a K-type thermocouple (fitted before the turbo) and dual gauge (turbo boost/EGT) from Westach (it is here: http://www.westach.com/images/showca...-Boost-EGT.jpg ). Not cheap but accurate and reliable.


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Roman (UK)
www.overlandcruiser.info