Alloy Heads and towing, how to help with overheating probs.

Submitted: Wednesday, Apr 02, 2008 at 20:25
ThreadID: 56210 Views:2368 Replies:5 FollowUps:5
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Was sitting with a group of tradies the other day at lunch, and
the conversation of towing with cars, trucks, etc, got underway,, but one guy made a statement that i've taken on board; and that was inregard to towing up a looong hill, then going down the other side, letting it go down on overrun with a tap on the brakes now & then. Not good for alloy heads as temps rise a lot more than shown on the guage, so its better to try and drive with a bit of throttle so as not let it cool to quick when on the down hill run.

Not allways possible, but alloy heats and cools very quick, so in my opinion i think he was right in what he said.

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Reply By: Member - David P (VIC) - Wednesday, Apr 02, 2008 at 20:51

Wednesday, Apr 02, 2008 at 20:51
so the theory is that the thermostat doesnt do its job ????
AnswerID: 296222

Follow Up By: Member - Axle - Wednesday, Apr 02, 2008 at 20:59

Wednesday, Apr 02, 2008 at 20:59
The thermostat dosen't control how quick it cools from one temp to another, :)).

Cheers Axle.
FollowupID: 562284

Follow Up By: zacc - Wednesday, Apr 02, 2008 at 21:35

Wednesday, Apr 02, 2008 at 21:35
i would have thought that the thermostat would start to close as the heads cooled down thus holding the heat in . the thermostat would open and close a lot faster that the head or heads could heat up and cool down , thus keeping the engine at the right temperature.
FollowupID: 562295

Follow Up By: Member - Kiwi Kia - Wednesday, Apr 02, 2008 at 21:40

Wednesday, Apr 02, 2008 at 21:40
Axle, as soon as the water temp goes down to the opening temperature of the thermostat it shuts and keeps the engine warm. Radiator will cool rapidly but the engine block will stay warm till it is cooled by airflow. The engine is still ticking over and hot oil is still being circulated and the engine should be cooling evenly.
FollowupID: 562298

Reply By: Davo_60 - Wednesday, Apr 02, 2008 at 21:34

Wednesday, Apr 02, 2008 at 21:34
It may cool quicker with a little throttle given the increased water flow and fan speed. Just surmising as I try to keep a little throttle on after a big climb to keep the fan and water pump working a bit faster in an effort to keep cooling.

AnswerID: 296239

Follow Up By: pt_nomad - Thursday, Apr 03, 2008 at 06:42

Thursday, Apr 03, 2008 at 06:42
my experience with a LC105 1HZ is that this is one of the most dangerous times as far as EGT is concerened. AFtr cresting a hill the tempation is to hold full throttle to allow the vehicle to build up some of the lost speed making use of the down hil run. My observations is that this action consistantly and v. easly this sends EGT into the 700+ region with very little effort.
So after cresting back off 30% for 10 secs and then poke the loud peddle to get some speed.
FollowupID: 562345

Follow Up By: Davo_60 - Thursday, Apr 03, 2008 at 19:45

Thursday, Apr 03, 2008 at 19:45
Thanks Paul,

I think we are talking about the same thing. I back off at the top of a hill but not to the point of no throttle. I will usually leave it in third (4 speed auto) to keep the revs up a bit until EGT drops and temp starts to reduce, then slip it into top.

FollowupID: 562488

Reply By: Mick15 - Wednesday, Apr 02, 2008 at 21:39

Wednesday, Apr 02, 2008 at 21:39
yea, i see what they are saying, obviously that wouldn't apply to a diesel as it will run cooler when lean, but with aluminium it conducts heat roughly 4 times the rate of steel,
Therefore i would assume that if there was any excessive heat generated then it would be wicked away from the combustion chambers fairly quickly and provided the cooling system is in good nick should then be transfered away...
Maybe if your coolant level was low or had an air pocket in the head there could be problems though, i'd still think that there would be more heat generated going up a hill under full power.

imho :)
AnswerID: 296240

Reply By: Member - David P (VIC) - Wednesday, Apr 02, 2008 at 22:12

Wednesday, Apr 02, 2008 at 22:12
you may not think you need anti-freeze, but it is an important anti-cavitation component, that is the formation of bubbles in areas of high turbulence eg the water pump impeller vanes which tend to gather in the highest part of the engine , the cylinder head combined in many instances with turbo and or supercharging The modern engine is being pushed to its limits to satisfy the requirements of reduced emissions, increased power and reduced consumption......silverback
AnswerID: 296256

Reply By: DIO - Thursday, Apr 03, 2008 at 10:10

Thursday, Apr 03, 2008 at 10:10
By allowing vehicle to coast ('angel over-drive') you not only run the risk of loosing control through increased speed but with engine only idling (say 500 - 700 rpm) water is not being circulated as quickly throughout engine/radiator as when say engine revs are at 1500 - 2500 (or whatever). If water pump is engine driven why not consider a electrically driven unit. Added benefit of increase in engine power and greater cooling efficiency. Link
AnswerID: 296321

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