BMC 1.5L Diesel measurement from Top of outer flange to bottom of thermostat

[Hunttm]

My BMC 1.5l marinised diesel engine has not been looked after well by the previous owner.

I am slowly going through bit by bit to fix the obvious problems.

In a renovation of the cooling system of ehich there were many problems I found that there was no thermostat.

I bought a new one to correct this omission. Specifically: https://www.asap-supplies.com/products/thermostat-82-c-with-bypass-shut-off-disc-199034

 

However, when installing I noticed that the depth of the thermostat would unlikely reach the depth to block the return valve.

See photos.

 

My question, maybe naively is;

- Is this correct?

- If it isn't what am I missing or where can I get a thermostat with the correct dimensions?

[Rincewind]

That is not how it works.

Rather than write a whole blog about it, you should slip the thermostat into a bowl or glass of hot water i.e. above 85 degrees C and observe what happens around the large flange.  (the anvil of your vernier gauge rests upon the flange)

[Tony Brooks]

and I don't think 1.5s use a bypass stat, or at least I can't remember them doing so, Maybe @Tracy D'arth or @bizzard will confirm.

 

I suspect the hole the OP thinks needs shutting off is the bypass, so the water pump will still maintain flow through the block and head when the thermostat is shut.

[Hunttm]

@Rincewind

Thank you for the quick response but would appreciate a little follow up to make sure I know what is happening.

 

I understand that the the larger spring at the top is to assist the open and closure of the thermo part of the thermostat. As you say if the liquid temperature reaches 82 degrees it opens to allow fluid to run through the radiator.

 

But what is the purpose of the lower smaller spring that looks like it allows the small base disc raise and fall in what I had assumed allows the return channel entrance during the engine warm up to open and close which you can see in the second image.

 

Or does this entrance just remain perminantly open whether the thermostat is open or closed?

[Hunttm]

3 minutes ago, Tony Brooks said:

and I don't think 1.5s use a bypass stat, or at least I can't remember them doing so, Maybe @Tracy D'arth or @bizzard will confirm.

 

I suspect the hole the OP thinks needs shutting off is the bypass, so the water pump will still maintain flow through the block and head when the thermostat is shut.

It is indeed the bypass and I guess my question is does this need shutting off when the engine is up to temperature and the thermostat open?

Or is it normal that the bypass is permantly open and I have the correct thermostat?

 

Thank you all for your repsonse and patience.

Shoot...just relised what is happening! 

 

My bad, I have the correct thermostat.

 

This video shows what is happening and how the bypass gets closed. 

 

https://youtu.be/aOXz5hlKO9s?si=uR0JxQwcBdLKjm_4

[Tony Brooks]

26 minutes ago, Hunttm said:

It is indeed the bypass and I guess my question is does this need shutting off when the engine is up to temperature and the thermostat open?

Or is it normal that the bypass is permantly open and I have the correct thermostat?

 

Thank you all for your repsonse and patience.

 

I THINK you do not want the one with the "washer" hanging down below it in a BMC 1.5D and you will note I asked two other members for their opinion.

 

I think that bypass is permanently open and by the time it gets to the bypass inlet to the water pump it is only about 1/4" to 3/8" ID. Await input/confirmation from others.

 

When the 1.5D was designed (say mid 1950s) there was not such things as bypass thermostats.

34 minutes ago, Hunttm said:

@Rincewind

Thank you for the quick response but would appreciate a little follow up to make sure I know what is happening.

 

I understand that the the larger spring at the top is to assist the open and closure of the thermo part of the thermostat. As you say if the liquid temperature reaches 82 degrees it opens to allow fluid to run through the radiator.

 

But what is the purpose of the lower smaller spring that looks like it allows the small base disc raise and fall in what I had assumed allows the return channel entrance during the engine warm up to open and close which you can see in the second image.

 

Or does this entrance just remain perminantly open whether the thermostat is open or closed?

 

The large top spring is to CLOSE the top disk valve. It is opened by a tapered rod hanging down, through a rubber bush, into the copper coloured "cup" on the centre of the thermostat. The cup is fill of a copper/wax mixture that is normally solid but as the engine heats up the wax melts, expands and pushed on the tapered rod to force the disk valve open. A bit like a cherry stone shot from between fingers.

 

The disc valve varies its degree of openness depending upon temperature.

 

The small spring allows the smaller bypass disk to slide upwards when/if the disk contacts the bypass port surround.

 

 

1 hour ago, Hunttm said:

If it isn't what am I missing or where can I get a thermostat with the correct dimensions

 

Any car parts place and ask for an 82 degree thermostat (either bypass or non-bypass once it is confirmed), or Calcutt Boats. Some marinises fit a cooler thermostat when a clarifier is in use to limit the domestic water temperature, say around 70 degrees.

 

[Tony Brooks]

As Tracy & Bizzard did not confirm what stat the 1.5 uses, I have been looking at the ASAP site and from the spares illustration found that the 1.5 uses a normal thermostat, but the 1.8 uses a bypass stat. That makes me wonder if a 1.8 head will fit onto a 1.5 block and if so, is yours a 1.8 head, or even have you misidentified your engine as a 1.5 when it is really a 1.8.

 

Look for big numbers cast onto the side of the block below the manifolds or if the injector pump is stick out the side of the block like a car distributor it is a 1.5. If it is parallel to the block and towards the front, it is a 1.8.

Edited June 27, 2024 by Tony Brooks

[Hunttm]

Had a look through my old ohotos and is definately a 1500.

[Tony Brooks]

12 minutes ago, Hunttm said:

Had a look through my old ohotos and is definately a 1500.

 

 

I agree, so unless it has had a head change, the ASAP site shows an ordinary non-bypass thermostat.

[Hunttm]

@Tony Brooks Perfect thanks.

[Tony Brooks]

I am sorry, but I am uneasy with what looks like a machined face around the bypass hole, it looks as if a bypass stat would fit and probably work. If you already have one, then fit it and as long as the thermostat flange does not sit proud, see how it goes. The lower disk moves down as the thermostat opens, and the calorifier coil circuit will act as a bypass circuit.