gq bonnet vents

Submitted: Saturday, Apr 08, 2006 at 18:44
ThreadID: 32685 Views:5599 Replies:7 FollowUps:7
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Just thinking the other day to combat my overheating problem on my gq turboed td42 engine wondered if venting the bonnet via a single or perhaps two bonnet vents might help?.I have read that a bonnet scoop seems to be not effective but bonnet vents might be?

Any suggestions?and as to where one might be able to get them.

regards andy
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Reply By: Member - Ian H (NSW) - Saturday, Apr 08, 2006 at 19:29

Saturday, Apr 08, 2006 at 19:29
Hi Andrewv,
A mate of mine with a 4.0 ltr troopie tried raising the back of the bonnet by putting about 30mm thickness of steel washers so that the heat could escape in front of the windscreen. If did work. Maybe you could try that before putting a vent in the bonnet (which is kinda permenant). At least you can remove the washers if it doesn't work. My guess is it will make a bit of difference but not what you are looking for. The 4.2 (turbo or not) does get a bit hot under load and thats's that.
Many have tried to fix it but I think all have given up. At least it is one Nissan that you CAN"T blow up. A good tough donk and I've got a 4.2 turboed 80 series.
If you try it, post the results for others.
AnswerID: 165834

Follow Up By: andrewv - Saturday, Apr 08, 2006 at 19:44

Saturday, Apr 08, 2006 at 19:44
Thanks Ian for the response and having heard somewhere else that by raising the bonnet by 15mm via spacers can help.But in suggesting it to the Mrs that the bonnet near the windscreen will be up by 15mm she said that bonnet vents will look nicer BUT I will try the spacer alternative just to prove a point.I will post the results as soon as we have them which might be later this year as we in Victoria are experiencing rather chilly days and I am sad to say the Hot days are gone.

regards andy
FollowupID: 420731

Follow Up By: Trevor R (QLD) - Saturday, Apr 08, 2006 at 21:04

Saturday, Apr 08, 2006 at 21:04
I have to agree with Ian, regarding the tendancy for this motor to run hot under load but I will disagree that they can't be blown up. The Brother in law is testament to this after just getting his GQ back this week due a completely thourough blown 4.2 diesel engine. Solution was to put another one in it was that bad. I don't know the full reasons behind the failure (if you could call it a failure with 400+ thou km on the clock). Ian is right that they are a DAMN TOUGH ENGINE THOUGH.
Even the GU that I have runs hot but I have still got a hard earned 260 thou on mine already without too much drama.

Cheers Trevor.
FollowupID: 420757

Follow Up By: Marn - Saturday, Apr 08, 2006 at 23:21

Saturday, Apr 08, 2006 at 23:21
I have to agree with them being tough. We used to run them where i work and they were unstoppable! I drove 1 from the 18 level to the surface(read 15 min on redline) with the gauge on the stoppers without a problem. Once up top the motor cooled down and everything was as good as gold!
You gotta love company cars!!

Cheers Gerard
FollowupID: 420785

Reply By: 93maverick - Saturday, Apr 08, 2006 at 19:45

Saturday, Apr 08, 2006 at 19:45
The problem could be sludge in the engine block. There is a drain plug at the back side of the block. Remove the plug and flush the block. This may solve the overheating.
AnswerID: 165843

Follow Up By: 93maverick - Saturday, Apr 08, 2006 at 19:47

Saturday, Apr 08, 2006 at 19:47
The plug is below the exhaust manifold.
FollowupID: 420733

Reply By: andrewv - Saturday, Apr 08, 2006 at 20:09

Saturday, Apr 08, 2006 at 20:09
Thanks I just have completed flushing the block out with CEM oil flush product just the other day and noticed no sludge being removed (perhaps the previous owner "Father Inlaw") maintained it properly hence the reason I bought it off him.I also changed back to valvoline 15w40 grade oil from Penrite 20w50 which I thought was a bit thick.

regards andy
AnswerID: 165848

Follow Up By: Member - Roachie (SA) - Saturday, Apr 08, 2006 at 22:59

Saturday, Apr 08, 2006 at 22:59
I think 93Maverick was referring to the coolant needing to be flushed out using the plug under the exhaust manifold.

An unconfirmed story I have heard about the 4.2 Nissan motor is that a number of them have been produced without completely removing the casting sand from the water galleries. This, it is said, causes the coolant to not circulate properly.

I have tried many things to stop my GU from over-warming.........(note, I refuse to refer to it as "overheating" as that implies that the motor has ceased to operate at some stage..........mine has never let me down). I have spent a lot of time on this forum typing out the long list of what i have tried etc.

Basically, the 1st thing you need to know is that just because the temp gauge needle nudges up towards the right side of the gauge, it doesn't mean you have a least not until the needle gets into the small 'extreme' section (provided your gauge is doing what it was intended to do). I didn't trust the gauge and wanted to know what the rael temp is, so I fitted a VDO gauge in the top radiator hose. This new gauge shows the temp properly. It is amazing that the OE gauge will sit on it's "normal" position (just below half way) from a coolant temp of from about 55oC to 105oC. Once the coolant reaches 105oC, the Nissan gauge's needle starts to rise quite quickly..........reaching almost into the 'extreme' section at around 120oC.

Now, as for the bonnet vent idea.........there is a bloke in Sydney known as "DB" (Dave Bradley). He used to be a tour guide for Great Divide Tours (the same mob that "Wayne NSW" works for). He used to own a GQ with a Safari turbo/intercooled 4.2L motor which used to get warm too. He had a bonnet scoop from a 3L Patrol fitted into his bonnet.......BACKWARDS (as a vent). It was located centrally on the bonnet, just behind the radiator. He reckoned it helped his GQ a lot. (that GQ was featured in an issue of 4WD Monthly several years ago, as was his next vehicle, a GU the same as mine).

I've put in a huge PWR aluminium radiator, a 3L Patrol's bonnet scoop above the turbo, moved my Lightforce 240's to the top rail of the bullbar, installed a 14" Davies Craig fan in front of the radiator to assist blow air through, put in a new genuine fan hub, tried a couple of different brands of coolant (Red Line was one and Amsoil's is what I'm currently using).

Mine only climbs up to around 105oC (with Nissan gauge still on 'normal') or sometimes a bit higher, on fairly hot days (mid 30's and above) and normally only when I'm towing the camper trailer at highway speeds. At New Year the temp on NY's eve after work was about 43oC and we were off to the Murray River. I didn't spare the ponies.....travelled @ 100k/h for about 3 hours with air-con on and with temp gauge sitting on or around the 115oC mark. I wanted to see what would happen. The old girl just took it in her stride.....never missed a beat and never slowed down or showed any ill-effects.

I know it's easy to say....but try not to worry about it. I wish I hadn't cut a hole in my bonnet and fitted the scoop, or spent $1100- on the PWR radiator etc etc....waste of money I think.

Cheers nad good luck

FollowupID: 420783

Reply By: JOEPATROL - Saturday, Apr 08, 2006 at 21:25

Saturday, Apr 08, 2006 at 21:25
Hi Andy

I have had this problem on my GQ 4.2 diesel turbo after chasing the fault for
about a year. and ran though all cooling system clean out new radiator etc etc
the fault turned out to be the fan clutch.After replacing it,( was a cheap after market one )with a diesel nissan 4.2 fan clutch NOTE these can be dissabled
and repacked with special fliud for the purpose from nissan dealer.
For a new fan clutch price was over $ 300 !
I used a genuine secondhand one from a wrecker $ 95
Problem was solved for me I havent looked back since.
I was told at 100kph there is not enough air flow through the radiator
there by needing a fan to keep temp under control, you shoud be able to just hear
it come on and off, while on highway or crawling offroad.Some mechanics slip a bit of (sheet) of cardboard inbetween radiator and front cross member to block air flow and make clutch warm up and engage for a test .Have not needed to do this myself though.

Hope this is of assitance

Cheers Joe
AnswerID: 165867

Reply By: Member-Neil & Margie-Cairns - Sunday, Apr 09, 2006 at 09:29

Sunday, Apr 09, 2006 at 09:29
Andy ,
I remember raising the bonnet on my torana "years" ago , was driving up one of the ranges around ( non to slow ) and a raditor hose blew , where does all the steam and dirty water go ,, can't see nothing !!

Won't do that again ..

Neil !!

Lifetime Member
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AnswerID: 165911

Follow Up By: revhead307 - Sunday, Apr 09, 2006 at 11:17

Sunday, Apr 09, 2006 at 11:17
yeah i think there is an ADR reg disallowing rear facing bonnet scoops etc for just that purpose.

Raising rear of bonnet could end up with same result.

FollowupID: 420842

Follow Up By: Jugs - Sunday, May 07, 2006 at 11:14

Sunday, May 07, 2006 at 11:14
Hi Just looking through the many posts re over heating and all the work every body has put in to solving it. All seem to work on the water side cooling system, but as some one else mentioned in another thred the water/radiator only dose 1/2 the cooling in any engine, Oil has 2 major jobs in any engine lubrication and cooling.

Just wondering has anybody tried adding a oil cooler ? or direct monited the actual oil temp ?
FollowupID: 426739

Reply By: Member - AVA 191 (QLD) - Monday, May 08, 2006 at 19:19

Monday, May 08, 2006 at 19:19
There are vents that are aimed at extracting hot air, and vents aimed at sucking cool air into the carby or airbox (Torana A9X style).

There's a good write up by a Jeep XJ wagon owner about the merits of bonnet vents. He did tests with his vehicle and explains what he did.

If you're still interested I'll try to find a link.
AnswerID: 171565

Reply By: Truckster (Vic) - Monday, May 08, 2006 at 22:01

Monday, May 08, 2006 at 22:01

Now back to the real world.
I have been through all of this in the past with my GQ - its expensive but can be sorted out..

What have you checked/replaced so far, this would assist in answering you.
Vents MAY assist, but they will only mask the problem... They may do nort too.. so before you go hacking your bonnet, and then creating more issues for places where water can go into engine bay when you cross rivers etc, read on.

What turbo, and how much boost?
Have you had the fuel pump setup properly?
Have you had the injectors o/hauled?
have you replaced the clutch fan?
Have you replaced the radiator?
Have you replaced the rad cap?
Have you replaced the rad hoses?
Have you replaced the temp gauge sender (dont laugh, it fixed my mates problem - it was a dodgey gauge), I too have gone to a VDO Gauge over the 14yr old OEM one.
Have you had the head checked for cracks?
Have you checked the fan blade for cracks or damage?
Have you physically removed the radiator and cleaned the fins WHILE removed (without removing it you only hose out 70% of it max).. while its out stick a hose in the bottom radiator hose part, and flush it all out the top of radiator.. (reverse flush)..
Have you had the radiator checked for internal blockages?

Just a few things to go on there.
AnswerID: 171627

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