Thermostat?

Ok,

After a couple of weeks, the lower radiator pipe is still freezing cold after driving about 8 miles through traffic in this cold weather. Top pipe roasting hot.

And yet bizarrely, I can return to my car half an hour later and the lower pipe has now warmed up!

Im guessing the thermostat is stuck though.

But I don't get it because the temperature guage shows as normal and the cabin warms up nicely.

Reply to
Simon Dean
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If the thermosts working it reduces the flow through the radiator, so the bottom hose gets cold. if it sticks open then the bottom hose is warm.

Reply to
Duncan Wood

Can't it stick in both open or closed? Surely if it's closed, no water will travel to/from the radiator.

Seems you're suggesting that open is the default state and it closes when the engine is cold.

I thought it was the other way round so that it stays closed to warm the engine up, then opens to allow water to flow through the radiator.

Reply to
Simon Dean

Simon Dean was thinking very hard :

The stat opens a little, the water flows slowly into the rad and because the weather is cold, the flow out the bottom is cold.

The flow continues into the rad due to convection and because there is not much air flowing past the rad to cool it, the water is still warm by the time it gets down to the outlet.

There you go then - all working normally :')

Reply to
Harry Bloomfield

Well then I sitll don't get it. Why is my 1.8 Nissan Primera a cool runner? The Nissan guides suggest when changing coolant, to leave the engine running at 2000rpm with the radiator cap off and wait for the lower hose to go warm.

I must have been revving the engine for ten minutes and it didn't get warm until I stopped the engine.

Water just kept gurgling into the radiator from the top hose red hot and far from overflowing, it just kept splashing out through the filler cap.

Ta Simon

Reply to
Simon Dean

on 13/11/2009, Simon Dean supposed :

Some engines, even when compared to identical models, can run very cool

- or rather they produce very little waste heat. My Granada of ten or so years ago, was like that. You could do an high speed 100mile run in hot weather, park it engine running in the garage, blank the rad with cardboard and it would still need to run for an hour before the two stage cooling fans would kick in. I did this to try to work out why I had never heard the fans run. There was nothing wrong with the fans, it was just an extremely efficient engine.

You didn't mention this.

Is this a modern one with thermostatic electric fan, or directly driven fan by the engine? Directly driven would mean rad would be cooled even when not moving.

Just keep an eye on the level for a while and top it up as necessary. They suggest running the engine as you do the final topping up to prevent airlocks. Be concerned if it does continue to need topping up.

Reply to
Harry Bloomfield

If it stucl closed it'd right the engine off, there's a bit of effort gone into ensuring they do the opposite :-)

Reply to
Duncan Wood

Simon Dean pretended :

It is not impossible for it to stick close, but it is highly unlikely. The very old designs of stats did stick closed, then along came the Waxstat and its main claim to fame was that if it failed, it failed open. Now all modern ones fail open.

Closed when cold, then it gradually opens to let the water through - but only as wide as needed to hold the correct temperature in the water jacket. Failure = open by design.

Reply to
Harry Bloomfield
[...]

Although up until the early seventies, the common failure mode was to stay closed!

Chris

Reply to
Chris Whelan

Sorry... thought maybe waiting for the thermostat to open once everything got hot to ensure everything was circulating was standard. And I guessed that the lower hose being closed indicated a thermostat being closed. What I don't know if there's a fault.

It is a fan of the type you mentioned. Car is from 2001, so driven electronically. Never came on. Never did a damn thing. Water temp guage shows correct temperature, can't fault it. But the fans didn't come on and the lower hose didn't get hot.

The first day after changing the coolant though, I did notice the temp guage go up quite a bit, and the coolant level in the reservoir go down. Topped up a little bit, temp guage and water level seem stable now.

By the sounds of it though, the engine probably is running normally?

Reply to
Simon Dean

Hence waxstats total domination of the market. Does anyone still have an old style one fitted? That's taking originality to absurd levels.

Reply to
Duncan Wood

Yes. Do it in summer &the bottom hose will get hotter.

Reply to
Duncan Wood

Simon Dean used his keyboard to write :

Yes, as near as I can tell from your descriptions it seems to be spot on.

Reply to
Harry Bloomfield

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