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Two Letters Re: Bug Out Vehicle Cooling Systems for Extreme Emergencies

In his recent contribution, “The Oddshot” stated that leaving a thermostat out of an engine is an unacceptable option: “So why not just leave the thermostat and blanking sleeve out entirely? Because the water will flow, unrestricted, and very fast through the engine and radiator. Too fast to pick up the heat from inside the engine, too fast to get cooled off in the radiator.”

I mean no offense to him, but this is an incorrect assertion. A coolant can never flow “too fast to pick up heat” or “too fast to get cooled off”. It is true that each unit of water will spend less time against the hot engine or cool radiator and thus will gain or lose less heat on each pass. But the decrease is exactly proportional to an increase in the total number of units of water passing a given spot per unit of time. The total heat absorbed and dissipated by the system will be exactly the same.

As a simple illustration, consider an open system where water is pumped into the engine on one side and allowed to drain into a lake on the other. Is there a flow rate at which the water will be traveling too fast to cool the engine down? Not at all. The same works on the radiator side: Less heat is dissipated by each unit of water, but more units pass through the radiator per unit of time.

That said, there are minimum and maximum ideal flow speeds that are dictated by the need to prevent scale accumulation and turbulence, respectively. Also, the minimum flow velocity is partially determined by the need to get the coolant off the engine and into the radiator before it boils. But there is simply no upper speed at which the water will cease to cool the engine. This is simple physics. Best, – Matt R.


Regarding Oddshot’s very informative article, here are a couple of things that I learned on the subject that were not mentioned.

1. A very difficult problem to diagnose (even by a good mechanic) is when your vehicle is overheating and you have checked everything Oddshot mentions but still it overheats. What could still be an issue? Some vehicles require that the lower radiator hose (the big one at the bottom of the radiator) is a hose that is equipped with a large spring on the inside of the hose. Most people wouldn’t know this because they didn’t install it, never have seen the inside of such a hose or just have never considered the anatomy of your cooling system. It is a bear to diagnose because you are usually doing the diagnosis by yourself. You drive, it overheats. You get out of the vehicle and look for everything and all seems ok. What is happening is that the lower hose while sitting at idle speed is good to go. However, when you drive and build some speed/pressure, that lower hose will collapse and therefore shut down the flow of water-coolant mixture. Your problem is that you couldn’t see the collapsed hose while driving. What happened to my spring? It eventually rusts out, breaks and disintegrates while your hose/clamp all is still intact on the outside. Just find out if your vehicle requires such a hose/spring type item and have one on hand. It takes awhile for that spring to rust out so keep that in mind.

2. Keep some cork (from your wine bottles) / tampons on hand with the other stop leak products for that larger emergency hole in any part of your cooling system. That is an easy “plug it and move on” [with the system de-pressurized] until you get to your destination. Trying to do things right when it is freezing cold, night-time, raining, snowing, in a hurry or in the wrong neighborhood may add problems.

3. Blanking sleeves: Maybe Oddshot can respond to this but I think the same effect can be had if one loosens the radiator cap to the point where it’ll stay on but is not secured to the tightest position and will allow some air/heat to escape from the system. Everybody knows where the radiator cap is on their vehicle. I think this would be a very temporary fix for late model go-fast vehicles and a more usable solution for older vehicles. The key is how much will your vehicle take as far as imbalances. I guarantee that a 1970 [vintage car or truck] from most any maker can handle that pressure change, but your 2009 Porsche or Mercedes Benz will have a hissy fit. Good Luck, – flhspete