410 running too cool

[David C]

My 410 is up and running quite nicely now but the temperature drops to about 55C on the motorway at 70MPH. I thought the thermostat was to blame so swapped out for a new Gates 82C unit without any change.
I have checked the temperature gauge and that seems fine. The car runs at around 70 to 80 on A roads and around 80 to 90 in slowish traffic until the fans cut in.
I have a transmission temperature gauge and that shows around 60 on the motorway and up to 90 or so pottering around the B roads.

Any suggestions?

[Geoff Kingston]

I would not worry about those sort of readings my first 603E which I hope to have back on the road soon always ran at different temperatures depending on road conditions with sometimes rapid variations whereas my current 603 once warmed up always settles at around 90/95. When I had the radiator on my 410 and 411 rebuilt they always tended to run cool so I could never quite understand the frequent comment that these cars overheated. The other thing to bear in mind as you now have a four speed box in your car is that the engine is not working hard at motorway speeds and that if you are not following a truck you will be getting maximum airflow through the rad.
Geoff.

[Nick Challacombe]

I do not see a problem, your running temps are fantastic and are backed up by gauges. My 407 runs much the same, took me years, new radiator with much bigger capacity, I control in town with an override switch as I have no thermostic control to the fans, which are the original 1962 factory fitted.
I would be extremely happy with your figures.

[David C]

It may seem odd to be complaining about running too cool but I have noticed with previous cars with more highly tuned engines that they run noticeably better around 80 to 90 degrees. 55 is just too low and is likely to result in higher fuel consumption, lower power output and more cylinder wear. I think the only culprit can be the thermostat so I will try an EMP / Stewart unit that has been suggested by folk in the US.

[Thor]

I would agree. Running at 55 is too low. The general rule is that you can't overcome the operation of a thermostat. The most common mistake is to fit a normal thermostat and then worry that the engine is too hot (generally it isn't) and then try to cool it with more fan power, which doesn't work because the thermostat always wins, it just closes a bit more.

In your case the thermostat must be sticking open, I think. It probably closes when the engine gets properly cold, but when it is just 25 degrees cooler than it should be the force is not enough to close it. Or maybe there is a significant by-pass route somewhere ?

I had heard that Stant is a maker of good quality thermostats, maybe track one of those down ?

[David C]

I have been doing a little more reading and came across this, specifically for Chrysler engines:
http://www.allpar.com/fix/engines/co...tem-about.html
The internet being what it now is, it is possible to find articles supporting all sorts of alternative truths, but opinion does seem to be largely against running for prolonged periods much below 180F / 80C

[Thor]

Yes, 80 would be a minimum, really. Maybe 75, but why ? 80 to 90 is fine and hotter is also OK if the system is pressurised.

[David C]

I ordered a Stant thermostat but a MotoRad unit turned up. It seems MotoRad bought the Stant name in 2022. Forum opinion in the US seems to be that quality has suffered.

[Nick Challacombe]

I drive a 1962 407 which as we all know was the first production V8.
I have had it 25 years and even when I bought it, it was known as a boiler.
The handbook suggest 90/100 as a running temp with a thermostat cap/ radiator pressure of 30 lbs sq in .
I cannot reach the facts as I am stuck in hospital so please forgive my memory.
The forum is essential reading! Thank you.

[AndrewA]

Had a quick look on Summit website - there's quite a selection of thermostats across quite a wide price range. On a previous car I got through 3 thermostats before I got one that worked as it should. I guess you could try the old suspending thermostat in saucepan experiment to see what's going on but you may well have other things you'd rather be doing.
Hope it's sorted soon and glad car is running well. For what it's worth (and presuming temp gauge is accurate) I'm 80 to 90 most of the time - it might creep towards the 100 if I'm stationary for ages when it's warm weather but fans don't let it get any higher.
Cheers
Andrew

[David C]

Nick - I do hope the hospital visit isn't serious and that you will be out soon.

I ordered both EMP Stewart and Stant thermostats just to be on the safe side. The car is at Transmission technology having its shift points adjusted. I will change thermostats when it gets back post an update.