From www.cranecams.com

cheers

Fred WB

Proper Coolant Temperature

Have you ever tried to find what proper coolant temperature is for most automotive engines? There are a lot of people who think they know, but it is difficult to find specifics, even in textbooks. We know we want the intake air to be as cold as possible (for best power) because cold air is denser (there are more oxygen atoms per cubic foot). The coolant temperature, however, is a different matter. The internal combustion engine changes chemical energy stored in gasoline into heat energy that is focused on the piston tops. If the cylinder heads and engine block are too cold, they will absorb much of the combustion heat before it can be used to push the piston down the cylinder. If the engine gets too hot, engine lubricants can break down, as well as overheating of the intake charge can lead to detonation, etc.

It turns out that coolant (usually a 50/50 mixture of coolant and water) has some fantastic properties that are ideal for use in engines. With a properly pressurized cooling system, coolant will not freeze until –30°F, and it won’t boil until +270°F (132C) (new oils don’t start to break down until well over 270°F). With these characteristics, engine designers have decided that engines should operate at approximately 210-215°F. (99-102C) Why, you ask? Well, it has to do with operating the engine at a high enough temperature to boil water out of the oil after the engine is cold started. If you have dew on the grass, it is certain that you have water in your oil, as the crankcase is open to atmospheric pressure! You can either remove the water by draining it out the bottom of the oil pan (remember the oil floats on water) or run the engine long enough and hot enough to boil the water out of the lubrication system. Years ago, coolants weren’t as sophisticated and engines were run at 165-180F, (73-82C) but the oil was changed every 1000 miles or so. That’s why many old timers think engines should run at 165-180F. (73-82C) Have you ever noticed that Ford doesn’t put temperature marks on their gauges? They just mark C for cold and H for hot and write “normal” through the center. If you hook up a scan tool to a GM, you will often find that the gauge reads much lower than the coolant temp sensor. That is because they know most drivers don’t understand how hot an engine should run.

So what does this have to do with camshafts? Many enthusiasts erroneously think that the colder their engine runs the better! If they are not running the engine hot enough to boil the water out of the oil, the oil becomes contaminated and the lifter/cam lobe interface is the highest load point in the engine. Engines running too cool can contribute significantly to camshaft and lifter failure. Think about it: What good does it do to use the most expensive synthetic oil and then run the engine so cold that it is contaminated by water vapor??!! Another point, piston manufacturers’ piston-to-wall clearance recommendations assume you will be running the fully warmed engine at 200°+F. (93C) Run the engine too cold, and you could see some scuffed pistons because the cylinders had not expanded enough to provide clearance.

If your engine will only run its best at the drag strip with the engine at 165°F, (73C) you probably have too cold of a spark plug heat range and you are probably jetted way too rich! If you keep the engine hot (not the intake charge), you will be using more of the heat energy in the gasoline to make power instead of just heating up your block. It does take “tuning know-how” to run an engine at 200-210°F (99-102C) , but you might be surprised how well and how long it runs when you do!! One final point - running a computer managed engine at 165°F (73C) compared to the factory 210°F (99C) will often cost you as much as 4 MPG. The reason for this is that the computer thinks that the engine is not off the “choke cycle” and it is still putting out a rich mixture! Check the science on this and don’t pay attention to the “old wives tales” of the past. Materials and lubricants are much better and different today than they were in the past!!

Interesting read, anyone got an alternative viewpoint ?

I was slightly surprised by comments in David Vizard's article in the latest PPC mag, where he advocates using lower engine temteratures (75-85C) as a means of reducing intake charge temperatures.

I'm very wary of questioning anything the man says, he has probably forgotton more about engine tuning than most of us will ever know, but the comments in the article reproduced by Fred do seem to bear out the importance of running engines at the 'correct' temperatures.

Seems to me that the potential downside to running an engine at a lower temperture far outweighs any potential performance advantage - or is my thinking fatally flawed (as usual)....

Maybe the route to follow is to run the water at the optimum temp for keeping the oil moisture free and using water injection to lower intake temps.

Perhaps DV was talking about competition engines where oil changes would be more frequent?

interesting reading...but is this right for all engines?
for example, will a low tune Ford crossflow and a (in a standard higher state of tune) Honda bike engine both be happy at higher temps than the standard 80 or so degrees...or does it purely depend on the oils characteristics?

Interesting reading. Kind of makes me comfortable that my fan kicks in at 98deg and switches back of at 94deg. Ive only just got it running, plain water for now whilst i debug the system and using components that ford didnt originally consider (ie std pinto bottom end, tuned top, no expension system, micra rad, no interior heater).


Sir Vizard is probably commenting on the coolant temperatures of an optimised tuned engine that will run under specific conditions and be treat with more service care than the average child.

Std automotive designers have to design a car for a multiple of users in a muliple of conditions. Some of which are numties in the damp UK so running at 98 -100+ sounds fair.

In fairness their wont be an optimum set of conditions that will suit all applications. Personally i would tend to follow Sir Vizard in the context of an engine for one of our sportscars as his experience is more suited to our application and follow Ford generic guidlines for my everyday Mondeo.



Interesting point about oil. Ihave often advocated without sound evidence that most engines do not need the very best (read most expensive) of fully synthetic oils. It is good pub crack and sounds good in an advert but in some cases iam sure the fully synthetics can have an adverse affect on the car. i am also amazed when i read" always ran on Mobil 1 and changed every 3,000 miles" then later it says "never raced or rallied". In other words "i have spent a trillion quid on oil, changed it before it has got ran in and never enjoyed the car"! Strange me thinks. Good quality modern mineral or semi synthetics for me.

[Edited on 4/11/05 by DarrenW]

I don't know what pressure standard caps vent at, but Stant caps are available set at:

19/20 PSI (1.31/1.38 bar), at which pressure plain water boils at 107/109 deg C

and

22/24 PSI (1.52/1.65 bar), at which pressure plain water boils at 111/113 deg C

Cheers

Fred WB

I once made a test rig for a specialist car maker in the UK that ran the car on a rolling road until the temperature reached 103°C. The test would pass if the temperature got this high and the fan switched on. This was a production test and all cars built were tested in this way. Clearly this is the way that the engine was meant to work.

The higher the water jacket temperature the less heat is rejected to the cooling system this can meam more power particularly for a turbo engine , of course this conflicts with keep the inlet air temp low and cylinder head temperatures within bounds..

Another balancing act is that the water jacket temp inlet should not be to low it causes condensation and the temperature evenly distributed through the block --- this is why cooling systems should always be plumbed with a radiator bypass to provide warm circulation within the block even when the thermostat is closed.

A lot of large stationary engines in generators and the like have two thermostats each of different temperatures in parallel to give more accurate control of the engine temperature.

Another trick for better temperature control is to use two electric cooling each switched at a different temperature -- the first time I saw this was on the old Rover 800. Later Rover used a 3 speed cooling fan set up on the 75 but the control system is complex.

As the title says,

just point at the rad, water hose, cylinder head, oil filter etc, and it tells you the temperature.

This bit of paper was 22.2 deg C

Paul G

[Edited on 4/11/05 by 907]
Rescued attachment temp-sensor-s.jpg

What happens if you point it at the sun? Being England though, you'll probably never know...

It tells you the temperature of


THE BIG BLACK CLOUD

Paul G

They are great tools.

First day i had it i spent all day measuring the temp of my cup of tea, the wall, the floor, my arm, etc etc.

But very useful when checking temperature flow in an engine and confirming the accuracy of the cars temp gauge etc.

David

Sorry getting off the thread a little.

I have great respect for David Vizard, but a lot of the sport he is involved in is short length i.e. drag racing.

He does however also advocate thermal coatings on the ports valves and chambers which may give the best of both worlds.

David