Thermostat missing?

MikeT · Unread post by **MikeT** » 03 Sep 2007, 19:12

I notice my temp gauge will sit at 80 max unless I'm wooshing down the road where it'll drop to about 75. Does this imply there's no thermostat or that it's stuck open?

Stempy · Unread post by **Stempy** » 03 Sep 2007, 20:04

Does it take a long time to warm up? Best way I know to check it is start from cold and grab the top hose, if it slowly warms up then you could have a jammed open stat, if it stays cold for quite a while and then suddenly gets hot then the stat is ok.

deian · Unread post by **deian** » 03 Sep 2007, 20:22

If it drops when you drive in the open air then it will drop down as the air entering the radiator will cool the water down. If you drive slowly around town then it will warm up because there is not enough air going into the rad.

Also as Stempy said, it hould start cold, the suddenly warm up at the pipes going into the radiator.

Another test is to take the thermostat out and drop it in a jug of tepid water, just so it's submerged, then add a kettle of boiling water, and watch it open, quite a fun experiment to do.

All sounds well to me!

MikeT · Unread post by **MikeT** » 03 Sep 2007, 20:29

I didn't want to drain the coolant unnecessarily to determine the problem so thought I'd ask here first. In this mild weather, the gauge is on the move before I've completed a mile but I'll do the top hose test suggested, thanks. Isn't 75 too cool though? I thought 'stats were rated for about 85-90. Or are these temp gauges too inaccurate for that?

MikeT · Unread post by **MikeT** » 04 Sep 2007, 09:56

Started from cold, fuel filter housing got hot within a few minutes while the top hose stayed cold so there is a 'stat and it's working fine.

I'm now curious to know why the temp gauge drops to about 75, shouldn't the 'stat keep the engine temp higher?

Unread post by **CitroJim** » 04 Sep 2007, 10:14

Old 'stats get lazy Mike and even though they seem to work, the spring weakens over time and allows the 'stat to open a little too soon. There is no rush to replace it.

The temperature gauge and thermostat reacts relatively slowly to temperature changes and the gauge is only reading the average temperature. A good fast but light run in cool weather often drops the temperature a little bit, it's the combination of the water pump spinning at a good speed, a light engine load and a good flow of nice cool air through the rad. It shows everything is in good nick

I use the above technique to keep the TD engine cool when towing. Come to a slight downhill, change down into 4th, let the engine run fast on trailing throttle and the temperature comes down a treat. Very useful when the temperature climbs high during a long drag up hill or through a congested town. Often if it gets a bit hot running along at 60mph in 5th, a change down to 4th allowing the engine and water pump to spin that bit faster will drop the temperature back nicely. A ton of caravan on the back certainly gives the cooling system plenty to do

Another little quirk is that from cold, the temperature as reguistered on the gauge will climb slowly to a quite high reding and then quickly drop back as the thermostat opens. A useful test of thermostat function as well. The thermostat has some hysteresis and again this can cause the fluctuations you see.

Unread post by **Peter.N.** » 04 Sep 2007, 10:30

If it's staying at 80c with no thermostat it would be in serious need of a new radiator, so I dont think that is the case, it is probably either not shutting properly or 'tired' as previously mentioned.

MikeT · Unread post by **MikeT** » 04 Sep 2007, 10:32

Lazy or tired spring seems probably - that's lads!