Car running cold?

[Lazy-Ferret]

OK, I have no idea how this works on a Diesel, my car has started to run cold...

Normally, I start her up on a cold morning, and by the time I have driven a mile, the engine is nice and warm, the temp gauge is about 1/4 of the way up, and by the time I get to 2 miles it is sitting at it's normal spot of just under the halfway point, and I have to turn the heater down.. This is a drive in traffic...

For the last couple of days, I can drive 6 miles, and the temp gauge is only about a 1/4 if that. I guessed at the thermostat, so got a new hotter one, but having fitted it, it is still the same. It's not the temp sender, as physically, the heater is only blowing luke warm air.

I also checked the old stat, and it is fine, so that was not the issue in the first place.

So, why on earth would my car suddenly start running cold, any ideas?

 

[clivvy]

air bubble in the rad perhaps? worse still, an issue with the heater matrix?

 

[Peasgood1]

If you fitted an 88C stat and it's still running cold, my guess is blocked heater matrix.
Usual cure is take both pipes off and flush it out with a garden hose.
Only other time i have known it to happen is if the coolant level is very low.
I assume you topped it up when you did the thermostat.

 

[Lazy-Ferret]

Yep all topped up and carefully bled.

It's the whole engine, not just the heater, after 6 miles, I can hold the top radiator pipe, it is that cool.

 

[R1cho]

sounds like a blockage in the rad to me

 

[solarman216]

I have not stripped a TDi to be sure, but sounds to me like a corroded hole in the alli thermostat housing, allowing water to bypass the thermostat, Rick

 

[rustic]

In the winter, I fit a blanking piece of ply behind the upper grill to stop too much air getting through and over cooling the upper part of the radiator.
I have also made one for the lower part of the rad, but I have not used that one for at least 5 years...:augie

Also the fan pushes loads of cold air into the engine compartment, so the engine is probably air cooled too.
So maybe it depends on what sort of driving you are doing in those 6 miles.

As a thought, could it be possible for the viscous fan to fail so that it is always running, thus over cooling the engine compartment.:nenau:nenau

This weather, I doubt you need the fan anyway, that's why an electric one seems a better choice.

Rustic

 

[Lazy-Ferret]

sounds like a blockage in the rad to me

Don't think it can be a blockage, as it is too cold, blockages generally make things hotter

I have not stripped a TDi to be sure, but sounds to me like a corroded hole in the alli thermostat housing, allowing water to bypass the thermostat, Rick

I obviously can not be certain, but basically the cooling system is very clean, even when I flushed it out last year, there was no rusty water. I think it has always had good antifreeze, as when I got it, it had the luminescent yellow/green, and I have replaced it all with the fluorescent pink stuff.

I had a general look round when I did the stat, and there were no signs of anything being corroded, there is not even any of the white "rust" on the outside.

In the winter, I fit a blanking piece of ply behind the upper grill to stop too much air getting through and over cooling the upper part of the radiator.
I have also made one for the lower part of the rad, but I have not used that one for at least 5 years...:augie

Also the fan pushes loads of cold air into the engine compartment, so the engine is probably air cooled too.
So maybe it depends on what sort of driving you are doing in those 6 miles.

As a thought, could it be possible for the viscous fan to fail so that it is always running, thus over cooling the engine compartment.:nenau:nenau

This weather, I doubt you need the fan anyway, that's why an electric one seems a better choice.

Rustic

Could be, I could unbolt the blades and see if that improves things. It would have to be just air flow round the engine though, as at the temp it is, the Stat is not even open, so there is no warm water in the rad to be cooled.

While waiting for my wife to come out the station tonight, I sat there for 10 mins with the engine ticking over, just to see if that would do anything, but it still did not get up to the 1/4 mark.

 

[solarman216]

Unless in arctic conditions the engine with a properly operating stat will maintain the stat temperature regardless, this is a very important part of engine design, as the load increases so the stat allows more cooling from the rad, less load, less cooling, if it runs cold then the stat is bad or the water has found another path, simples, regards Rick

 

[Banshee]

OK, I have no idea how this works on a Diesel, my car has started to run cold...

Normally, I start her up on a cold morning, and by the time I have driven a mile, the engine is nice and warm, the temp gauge is about 1/4 of the way up, and by the time I get to 2 miles it is sitting at it's normal spot of just under the halfway point, and I have to turn the heater down.. This is a drive in traffic...

For the last couple of days, I can drive 6 miles, and the temp gauge is only about a 1/4 if that. I guessed at the thermostat, so got a new hotter one, but having fitted it, it is still the same. It's not the temp sender, as physically, the heater is only blowing luke warm air.

I also checked the old stat, and it is fine, so that was not the issue in the first place.

So, why on earth would my car suddenly start running cold, any ideas?

I have noticed that my temp guage is def sitting lower than normal but even when the guage is only 1/8th from the bottom my heaters are blowing hot

Mine is an 82° stat, normal level at the moment in these temps seems to be a few mm below the normal level which in the summer was just below half way

 

[Lazy-Ferret]

I have noticed that my temp guage is def sitting lower than normal but even when the guage is only 1/8th from the bottom my heaters are blowing hot

Mine is an 82° stat, normal level at the moment in these temps seems to be a few mm below the normal level which in the summer was just below half way

Cheers for that, maybe it's the other way round, and it had a blockage, and now it has freed up, so I am noticing the difference in cooling... I will take her for a proper run, and see what she does, as these short journeys round town are not a good proving ground.

 

[macabethiel]

Sounds like thermostat failed open

 

[Banshee]

Sounds like thermostat failed open

Gold star to that man!!! I'm with his diagnosis :thumb2

 

[Lazy-Ferret]

Gold star to that man!!! I'm with his diagnosis :thumb2

It cant have... the one I took out opens and closed fine in a pot of hot water, and the one I put in, was closed properly, and I do not think it has got hot enough to open yet either.

 

[Banshee]

It cant have... the one I took out opens and closed fine in a pot of hot water, and the one I put in, was closed properly, and I do not think it has got hot enough to open yet either.

Run it with your rad cap off and see if it runs the same or different

 

[macabethiel]

Still think its the thermostat from what you have told us. The saucepan test is interesting when I have tested using this method the stat would struggle to open until it had been boiling for several minutes and would close almost immediately on removal. It is not possible for the engine to run cool it always generates heat from combustion.
That heat is dissipated by the water cooling system and the thermostat regulates the coolant temperature. So much heat is generated from the engine that you need a good water pump and heat exchanger (radiator) to stop it from overheating. Assuming that your statements about the radiator matrix not getting are right then coolant is finding
a way to escape from the engine to the radiator. That path is through the thermostat.

 

[wildbri]

could be the fan, normally from cold you can hear the fan running for the first 1/2 mile then it stops, only comming on when towing a caravan over a very large mountain in summer! If it is running all the time it does shift a massive amount of cold air and could keep the engine cool ,very cool this time of year. Can you hear it roaring away all the time?

regards bri

 

[Banshee]

That's mine at normal temp after 40 mins of driving, 82° stat, its 3° where I am, it usually sits just below half way in summer

 

[Lazy-Ferret]

Cheers, thats where it normally sits on mine.... but it was only half way up that far.

Well the good news it, it is the wife's birthday, and I took her out for a meal in Faversham, so the car had a nice run down the motorways.

I had a chance to give her a bit of a blow out, and as I was going up Detling Hill, it suddenly climbed up to the normal position, and stayed there. On the way back, it was back to normal, so I am guessing that there must have been an air lock in top heater pipe. Strange thing is, the water level has not dropped...

 

[Sweety]

If it's back to normal again I wonder if you poss have a faulty sender unit