engine cooling

[David Withers]

<snip>... it would seem sensible to me to set the electric fan turn-on point at or just above the 'stat fully open point. This should mean that the fan shouldn't come on very often and then only when really needed!

Mike, thanks for your useful addition to my brief comment. I agree with the switch-in point that you suggest, 95-98 degrees seeming about right. This allows the engine to reach an efficient operating temperature but the fan starts to take control if and when it moves closer to boiling.

Almost all of our Perkins non-marine engines were fitted with 82 degree thermostats in my day, and IIRC* we advised a normal running temperature of up to 102 degrees.

* It will be 12 years in March since I took early retirement. Some technicalities I recall with absolute clarity, other things are subject to 'senior moment syndrome'.

[Mike Stevens]

Hi David,

I know what you mean, where does the time go? I'm still in (nearly) full time employment but do suffer from increasing numbers of 'senior moments'!

95-98 seems a sensible temperature to me, but of course, with the pressure cap, the boiling point should be higher than 100, but at this time of the morning, and having just come back from a small party next door, I can't actually remember the finmer details!

It's good to be corresponding with you again....

Cheers,
Mike.

[David Withers]

No party for me, but I still had to resort to the internet to find the change in boiling point relative to pressure!

According to http://www.cdxetextbook.com/engines/coo ... ssure.html, the boiling point in a system fitted with a 13 psi radiator cap will be 118°C. I imagine that figure assumes that any coolant additive ('antifreeze') isn't of high enough percentage to have any notable effect, also that the cap is in perfect working order and there are no system leaks.

[TedTaylor]

I know what you mean, where does the time go? I'm still in (nearly) full time employment but do suffer from increasing numbers of 'senior moments'!.

Totally agree with you and David.

Working on something or in a meeting and suddenly forget a bit of knowledge that I used to use commonly so that ................ oh drat what were we just talking about ........... now what were your names again ...........

Ted (think that was my name)

[TedTaylor]

I imagine that figure assumes that any coolant additive ('antifreeze') isn't of high enough percentage to have any notable effect.

Yes and with an RD of about 1.1 (and I needed to double check that on't Internet!) the effect would be pretty minimal even at 100% concentration.

Ted (just remembered who I was).

[David Withers]

Ted, I understood that adding antifreeze to water notably raised its boiling point, but again needed to rely on the internet for confirmation that I wasn't having yet another 'senior moment'. I came across an EPA site which confirmed my understanding in a language I understood (I'm still a child at heart): http://www.epa.gov/kidshometour/products/coolant.htm

The EPA site mentions a 70/30 antifreeze/water mixture but we found, at Perkins, that with anything stronger than 50/50 there is a tendency for the antifreeze and water to separate (stratify) and the level of protection against freezing reduces accordingly. For that reason we advised that the concentration should not go above 50%.

On a slightly related note: We had a problem at Perkins in the early 1980s in that the available antifreeze compounds were unable to properly protect our new Prima diesel engine. Our Chemistry Lab worked with a major antifreeze maker to come up with a more effective spec, which was then adopted by the industry in general and resulted in a new British Standard. Not a lot of people know that (or would want to!).

[Alec]

Hello David,

doesn't also the percentage of anti freeze in the coolant reduce the coolant's ability to absorb heat as the percentage of anti freeze increases, i.e. the best coolant for heat absorption is plain water? Rather academic as there are other considerations such as reducing corrosion, but possibly an argument for not having more anti freeze than is necessary for freeze protection?

Alec

[David Withers]

Hello Alec,

I couldn't answer your question with any confidence, so another visit was made to Bing (I stopped using Google a long time ago as I grew tired of their daily pestering for me to "Install Google Chrome" and "Make Google your home page").

According to http://www.engineeringtoolbox.com/ethyl ... d_146.html:
"The specific heat capacity of ethylene glycol based water solutions are[sic] less than the specific heat capacity of clean water. For a heat transfer system with ethylene glycol the circulated volume must be increased compared to a system with clean water."
and:
"In a 50% solution with operational temperatures above 36°F the specific heat capacity is decreased with[sic] approximately 20%. The reduced heat capacity must be compensated by circulating more fluid."

The 36°F that they mention is just above the freezing point of unadulterated water of course. [I wonder why the US persists with the antique Fahrenheit system?]

[murcod]

Yes, anti freeze reduces the ability of the cooling system to transfer heat. Do a search on Redline Water Wetter as it is supposed to help increase heat transfer- a friend used it in his expensive modified Skyline turbo and said it worked (results checked via data logging.)

[James]

I've been considering waterless coolant — looks like it'll cost at least £100 to do the conversion though.