engine is only getting upto 70c after a long drive  even after blocking rad off 50 percent , however  lower  rad hose  is not hot  ,,  top hose is. 

is thermostat  on end of top hose as it goes into block ? howevr considering  top hose  is not hot  does that mean its not open -a diagram of coolant flow would be useful .

tia

As would a clairvoyant to know what your engine is and how many miles you consider a long drive to be.

 

My crystal balls tells me its a diesel and you are driving less than 10 miles at moderate speeds, in winter I could easily drive for 10 miles without the thermostat opening unless I accelerated up a hill.

ah yes  tdi   asv engine   8 miles but as coolant temp determines so much with ecu and  low oil temp is not good for engines i need this to get upto temp   quicker the better   

59 minutes ago, pjb1 said:

tdi   asv engine

And how good is the heater/Climatronic in your car? I'm fairly sure the issue is one of 2 things, but this is a good point as to which.

yes heater is good  ,,after a few miles   vcds  says  instrument cluster matches ecu  temp  . trying to understand whats going on but if urs is taking mies to get upto temp as well MMN

 

Thermostat is here (item 6): coolant pump - Octavia(OCT) [EUROPA 2003 year] (7zap.com)

Seems quite likely to be at fault, especially if 18 years old.

thats what i am trying   to understand  , which way does coolant flow ie from  under thermostat   out through bottom hose  through to rad when hot  and out of top hose ,, cos at min only top hose is warm    coolant flow diagram would be really good

 

 

I had the same engine, I changed the thermostat but it made only a slight improvement, if the engine sits at 70°C its probably stuck partially open with a bit of detritus but you would have some heat in both hoses in that case.

 

Mine would take 4 miles before the heater was working well but the stat would never open on very cold days unless I drove on an autoroute or gave it some beans up a hill, once opened and the water circulating the temperature regulated well.

 

The MK2 Octavia PD engine was better but still a long warm up time on cold days, bottom line is the TDi engines have a high thermal efficiency and on a cold day with the heater on full and airflow through the radiator even without circulation through the radiator they overcool with the circulation through the heater matrix.

 

My Yeti with the sliding sleeve waterpump is dramatically better, heater gives out warm air after one mile and the temp is up to 90°c within 2 or 3 miles even on the coldest of days.

 

That comfort and efficiency comes at a price of reliability though, the water pumps are the achilles heel.

6 minutes ago, pjb1 said:

thats what i am trying   to understand  , which way does coolant flow ie from  under thermostat   out through bottom hose  through to rad when hot  and out of top hose ,, cos at min only top hose is warm    coolant flow diagram would be really good

 

 

Generally into rad at top hose, out at bottom one.

28 minutes ago, pjb1 said:

after a few miles   vcds  says  instrument cluster matches ecu  temp

Well, that definitely points to a slow warm up caused by a stuck open thermostat. On mine (TDi 110) I have a good Climatronic, and gauge reading 90C after ~5 miles (50 to 55 mph cruise in NSL).

Interesting thread ! ( I've been driving around with lower part of rad shielded from airflow for the last couple of years 🤪 )

When it comes to a replacement stat for ASV units, what is the best to get ?

- VAG or 3rd party ?

- If 3rd party which to go for / avoid ?

3 hours ago, olddog said:

VAG

every time when it comes to any sensor for a VAG car.

well  am going for the stat  ive blocked off   the entire  rad with  little effect  ,,  its the  bottom hose which throws me being cold  ,,

 

 

 

If the stat's leaking/slightly stuck open, there may be only a little flow through the rad, so there will be a large temperature drop between in and out hoses. i.e. the rad can cool that small flow completely down so you can't feel any warmth at the bottom hose?

Thermostat isn't a sensor...

 

I replaced mine with a Gates one quite a few years and many miles ago and it's still fine.

 

There are a lot of brands around and I'm not really sure what other brands do thermostats.

Edited 8 December, 20214 yr by petrolbloke

3 minutes ago, Wino said:

If the stat's leaking/slightly stuck open, there may be only a little flow through the rad, so there will be a large temperature drop between in and out hoses. i.e. the rad can cool that small flow completely down so you can't feel any warmth at the bottom hose?

 

I think it's the other way around. If the stat is stuck open flow of coolant (and therefore cooling) is maximised, so it'll take longer for the engine to warm up and it may not get to normal operating temperature at all (depending on outside temperature and airflow over the radiator). When the stat is cold it limits the flow of coolant and it opens as it warms up.

Let me clarify.

When I said there may be only a little flow, I meant as opposed to none at all, as it should be until operating temp is reached.

If there was lots of flow (stuck wide open) then the OP would be able to feel warmth at the bottom hose as well as the top one, I think.

i think what  a lot of people do not know is  ecu  takes  this temp  and gears all sorts to that temp  inc mpg    power  all sorts and oil needs to be hot to function properly ,,my mate  similar engine gets upto 90c   in 3 miles 

update   it   was the thermostat opening to early  so car is having some tlc  at min as we have found other issues =will start  other threads rather than mixing them up