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Temperature of coolant

Ken G

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Having had my magneto repaired, and also obtained a spare so I will not have to return home a third time on a flat-bed truck for a failed magneto, so the car is running again, I have another silly question.

I had noticed that after a run, I could almost bear my hand on the top of the radiator. I also observed that the Motometer never registers, although it works fine if I immerse the end in nearly boiling water. I therefore measured the temperature of the water at the filler just after a 25-mile trip, and it was 151 deg.F (with air temperature in the upper 60s). That seems low to me. Has anyone any ideas on the expected running temperature of a 1925 car? Remember that this is not a pressurized system. There is a thermostat, but I had already concluded that it was partially stuck open (see a string a year or more ago). I have a 6-bladed flexfan in place of the original 2-blade cast aluminum one, so it is possible that the engine is over-cooled.

Ken G, 1925 Rover 16/50 (San Francisco)

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After a 25 mile run my 1933 Packard 12 runs about 155 to 160 degrees in 60 degrees ambient temperature...if I close all the hood doors to keep the engine compartment as warm as possible, otherwise she runs between 148 and 153 degrees. My 1932 Cadillac V8 doesn't even register a temperature on such cool days. I live in southwest Florida. During summer days I open all the hood doors on the Packard and she will run between 160 and 165 degrees. The Cadillac will register in the mid-cold range.She's never runs in the normal or hot range. I've driven the Packard 4,500 miles and the Cadillac about 5,500 miles with no deleterious effects from cool running. Both engines have been taken apart more than once and inspected. Just be glad you don't run hot.

Postscript: My Packard has a Winterfront automatic shutter mechanism. You either have it or a thermostat. The Winterfront is designed to be fully open at 160 degrees. That's just 9 degrees higher than what your Packard is running.

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Probably over-cooled.

'15 Stellite which was thermo-syphon {no water pump Vern} ran consistent 195degrees. Vauxhall stays at 185 driving,195 idling, Horstman 200.

I had a Nash 980 that was happy at 165 bone stock,the Essex was prone to boil over on account of a milled head and a paper thin rebore for "power"{one of my mistakes}

If everything is clean and free and there is no smoking, loss of power or boiling over simply accept it.

You cannot apply modern standards of temperature regularity and performance to such an old design, no matter how well"restored"because all we do to these early cars may or may not be what was done when they were new, particularly on account of the individual engine designs of the epoch of which there were so many and varied, who all sought to find the philosophers stone of durability and performance. frown.gif

AS ALWAYS simply my 2 shekels worth..............

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(Looks like "old Crabby" types faster than I do... laugh.gif )


I would say that your engine is indeed over-cooled.

Before the advent of so-called "Permanent Anti-freeze" (Prestone, or other ethylene-glycol coolants), most auto thermostat systems ran no warmer than 160 degrees F, as temps warmer than this tended to boil-off the methanol anti-freezes then commonly available.

This was the "standard" engine operating temperature from the mid to late '20s through about 1950. When "permanent" antifreezes came along, they permitted higher operating temps, and 180 F became "standard"...then pressurized cooling systems were developed, thus raising the boiling point of the system, and allowing higher temps yet.

It was not until the late '20s or early '30s that auto engineers began to realize that "colder is not always better" when it came to engine temps - up to this point, they were more worried about equipping their cars with a cooling system that would prevent it from boiling over... but when the engine temperature stays below 180 F, the oil temp lags lower yet, and condensation tends to form in the crankcase (or carter, if you like) and contributes to sludge. Plus, colder engines required running with richer fuel mixtures (often obtained by running with partial choke), less than complete combustion, crankcase dilution, and in general, everything that's really bad for an engine.

Add to that primitive (non-detergent) motor oils, dusty roads, no oil filters, splash oiling on many period cars...

The cold-cranckase problem is further exacerbated by "short trip driving", where the crankcase contamination is at its highest, and the engine has even less chance to get warm and "boil" some of this garbage out of the engine oil.

A good thermostat and 180 F operating temps help overcome this to a good extent.

If I remember correctly, your Rover has a huge crankase (measured in gallons, instead of the usual quarts); I'm figuring it has an equally mammoth cooling system...it apparently is more than equal to the task, so I would not have any qualms about getting a t-stat in there that will keep it around 180 F.

If an OEM stat is not available, I think I've seen thermostats that can be fitted into the upper radiator hose.

It would also be worthwhile to find out of your Rover has any sort of "bypass" circuit in the engine block which allows coolant to circulate through the block while the engine is warming-up and the radiator stat is closed...

For more info on the theory of engine operating temperature, I would suggest a great little book called: "Drive It Forever", by Robert Sikorsky, S.A.E.

I picked-up a copy nearly 20 years ago, and still refer to it often. He goes into the whys & wherefores of how to make your car last as long as possible...

Hopefully it is still in print.

Good Luck! Hope you've seen the last of the flat-bed!


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I agree. Hotter an engine runs, the better. This was not true in the old days, when the primitive oils would 'thin out' and 'coke up', with bearing damage and sticky valves.

With today's oils, I use thermostats in all my vehicles (and I have owned vehicles from pretty much every era) that get them as hot as I can.

( the above presumes a cooling system that is in good condition )

Dog Spot

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Many thanks to you all. When I had the top of the engine apart (to fit new exhaust valves), I tried to dismantle the thermostat housing, a sort of brass (I think) dome with large holes through which I could see the thermostat. It, the thermostat, was partly open, but I couldn't remove the dome top to get at it. I was afraid of breaking the housing, so I gave up, having put the whole in hot water to establish that the thermostat did open still more. In fact, it looked to me as if there was a screw adjustment on the top of the thermostat, presumably to set the degree of opening at some defined temperature. Yes, there is a small bypass pipe, which suggests to me that the thermostat is supposed to close completely when the water is cold. Perhaps I should take it all apart and try again. However, it might be sensible to fit a fan with only two blades (per the original) instead of the present six and see what happens.

Ken G, 1925 Rover 16/50 (San Francisco)

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Two blades vs. six...

Well, the primary purpose of the fan is to provide airflow through the radiator core when the vehicle is standing still, moving slowly, or driving in a tail-wind...

If it's not too much trouble to change the fans, you could see how it is with the OEM two-blade...

Here's an idea: why not see if you can find two water outlet necks with "straight-up" necks (I am thinking of something from a 318 MoPar V-8), bolt them together flange-to-flange with gasket & appropriate thermostat inside, oriented correctly, and put this whole gizmo into your upper radiator hose, keeping the assembly as close to the engine block as possible...this would give you a fairly cheap and easy way to retrofit a modern t-stat into your car, with no mods to your vehicle, except for the rubber radiator hosing...

If you can do it, I think getting a working t-stat into the picture is the best solution...

Good Luck!

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