P38A Thermostat 2.5 DSE

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gencybay

gencybay

gatvol
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Read through a number of the old posts on this, particularly noting @wammers description of how the heater matrix is unregulated in order to give a fast cabin heat up.

Even after a two mile drive, Nanocom tells me that the coolant temp is around 60C.

Grateful for confirmation that, after 22 years, the thermostat is probably FUBAR.

The STC3338 opening them spec is 80C
 
gencybay said:
Read through a number of the old posts on this, particularly noting @wammers description of how the heater matrix is unregulated in order to give a fast cabin heat up.

Even after a two mile drive, Nanocom tells me that the coolant temp is around 60C.

Grateful for confirmation that, after 22 years, the thermostat is probably FUBAR.

The STC3338 opening them spec is 80C
Click to expand...
Two miles may not be far enough to get up to full temperature if the viscous fan is fitted.
 
Datatek said:
Two miles may not be far enough to get up to full temperature if the viscous fan is fitted.
Click to expand...

That's why @wammers post interested me. Effectively the heater matrix heats before the overall coolant temp comes into play. Until the stat opens, it is a very short circuit and the cabin should warm almost immediately.

If the stat is opening early, that benefit is lost.

So, even if the overall coolant temp isn't reached in two miles, the heater matrix should be around 80C near immediately.
 
gencybay said:
That's why @wammers post interested me. Effectively the heater matrix heats before the overall coolant temp comes into play. Until the stat opens, it is a very short circuit and the cabin should warm almost immediately.

If the stat is opening early, that benefit is lost.

So, even if the overall coolant temp isn't reached in two miles, the heater matrix should be around 80C near immediately.
Click to expand...
Even the heater on my 2 is not fully effective in 2 miles in cold weather and there is nothing wrong with the stat in either of them.
 
Where is the needle at this time? When you start up coolant is circulated through the block, head and heater only until the stat opens. On a cold morning when the stat opens and circulation is directed through the cold rad the temp will dip considerably for a while as the cold coolant from the rad circulates through the system. Is your viscous fan sound, it should not be driven by the engine until the temperature within the cowl activates it. Maybe it is stuck partially engaged. Normal cooling is done by ram air whilst driving, the viscous should only be engaged when the coolant temp approaches maximum, for instance in traffic after travelling at a sustained speed, to get rid of latent heat at low RPM with little of no forwards motion. Shortly after moving off again when latent heat has been controlled and circulation temp returns to normal due to ram air, the fan should almost totally disengage. It is very unusual for a wax stat to fail open, not impossible, but very unusual, they normally fail shut.
 
wammers said:
Where is the needle at this time? When you start up coolant is circulated through the block, head and heater only until the stat opens. On a cold morning when the stat opens and circulation is directed through the cold rad the temp will dip considerably for a while as the cold coolant from the rad circulates through the system. Is your viscous fan sound, it should not be driven by the engine until the temperature within the cowl activates it. Maybe it is stuck partially engaged. Normal cooling is done by ram air whilst driving, the viscous should only be engaged when the coolant temp approaches maximum, for instance in traffic after travelling at a sustained speed, to get rid of latent heat at low RPM with little of no forwards motion. Shortly after moving off again when latent heat has been controlled and circulation temp returns to normal due to ram air, the fan should almost totally disengage. It is very unusual for a wax stat to fail open, not impossible, but very unusual, they normally fail shut.
Click to expand...
The fan always turns pushing cold air over the block and drawing air through the RAD, true it turns faster when things get hot, but it still slows warm, more noticeable at low speed.
 
Datatek said:
The fan always turns pushing cold air over the block and drawing air through the RAD, true it turns faster when things get hot, but it still slows warm, more noticeable at low speed.
Click to expand...

No it is supposed to freewheel and is only turned by friction until engaged. It should be quite easy to stop with a bare hand when the engine is just warm. I somehow doubt that the air flowing over the outside of the block either produced by a slowly rotating viscous fan or forward momentum has any effect on engine warm up.
 
wammers said:
No it is supposed to freewheel and is only turned by friction until engaged. It should be quite easy to stop with a bare hand when the engine is just warm. I somehow doubt that the air flowing over the outside of the block either produced by a slowly rotating viscous fan or forward momentum has any effect on engine warm up.
Click to expand...
Put an anemometer behind the fan at cold idle, it produces a fair old air flow. If the car is moving at a reasonable speed, it will have little effect, but it certainly does when stationary or crawling in traffic.
 
Datatek said:
Put an anemometer behind the fan at cold idle, it produces a fair old air flow. If the car is moving at a reasonable speed, it will have little effect, but it certainly does when stationary or crawling in traffic.
Click to expand...

The fan turns but it should not be engaged. If it cannot be stopped easily by hand in that circumstance it is faulty. Have done this test to dozens of them over the years.
 
gencybay said:
That's why @wammers post interested me. Effectively the heater matrix heats before the overall coolant temp comes into play. Until the stat opens, it is a very short circuit and the cabin should warm almost immediately.

If the stat is opening early, that benefit is lost.

So, even if the overall coolant temp isn't reached in two miles, the heater matrix should be around 80C near immediately.
Click to expand...
no it wont,you will get little heat till engine warmed which will be struggling at 2 miles
 
gencybay said:
Read through a number of the old posts on this, particularly noting @wammers description of how the heater matrix is unregulated in order to give a fast cabin heat up.

Even after a two mile drive, Nanocom tells me that the coolant temp is around 60C.

Grateful for confirmation that, after 22 years, the thermostat is probably FUBAR.

The STC3338 opening them spec is 80C
Click to expand...
if you have off road parking fit an electric preheater
 
wammers said:
When you start up coolant is circulated through the block, head and heater only until the stat opens.
Click to expand...

Yes. That is what I undestood from your older posts.

wammers said:
the fan should almost totally disengage. It is very unusual for a wax stat to fail open, not impossible, but very unusual, they normally fail shut.
Click to expand...

I'm not thinking of a total failure, just that over time the springs properties may have changed and that it is opening at a lower temp than it would have done when new, diverting all that nice warm water to the rad.

I'm a bit surprised that you and @Datatek haven't suggested a radiator blind like you used to have in the fifties.
 
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