Pampered engine still overheating (BMC 2.2). Advice please!

Thank you everyone for the input here.

Having done some various investigations this weekend with a more mechanically minded friend than myself I have made some progress on this one! It turns out I was reading the temperature with my laser thermometer in a silly place (on the exhaust gasket which, apparently, will always be effing hot!) we run the temperature up to the point where the thermostat kicked in and saw a change in flow within the header tank so I am now confident that the thermostat is working as it should. With the header tank cap off we then let the engine hit 97° on the gauge and the water within the header tank was still cool enough to dip your finger in.

The conclusion was that the sender and or gauge are faulty or are not matched (i.e. have different resistances).

My next (and hopefully final) question is whether anybody knows the thread size of the temperature sender on a BMC 2.2?!

I will be aiming to replace both the gauge and the sender in one hit to rule out any compatibility issues. if anybody could recommend a matched pair which would fit my engine and 52 mm gauge cut out then I would be most grateful and also very impressed!!

I have already learnt a heck of a lot about diagnosing engines from this thread so thank you all for your input regardless of whether it was applicable to this situation or not.
All the best, Mike
 
Where is the temperature sender screwed in, the cylinder head, the thermostat housing or the heat exchanger/exhaust manifold?

If its in the engine I would bet its either 1/2" or 3/8" BSP.

If its in the heat exchanger it could be anything depending on the maker of the casting.
 
mikeakc said:
Thank you everyone for the input here.

Having done some various investigations this weekend with a more mechanically minded friend than myself I have made some progress on this one! It turns out I was reading the temperature with my laser thermometer in a silly place (on the exhaust gasket which, apparently, will always be effing hot!) we run the temperature up to the point where the thermostat kicked in and saw a change in flow within the header tank so I am now confident that the thermostat is working as it should. With the header tank cap off we then let the engine hit 97° on the gauge and the water within the header tank was still cool enough to dip your finger in.

The conclusion was that the sender and or gauge are faulty or are not matched (i.e. have different resistances).

My next (and hopefully final) question is whether anybody knows the thread size of the temperature sender on a BMC 2.2?!

I will be aiming to replace both the gauge and the sender in one hit to rule out any compatibility issues. if anybody could recommend a matched pair which would fit my engine and 52 mm gauge cut out then I would be most grateful and also very impressed!!

I have already learnt a heck of a lot about diagnosing engines from this thread so thank you all for your input regardless of whether it was applicable to this situation or not.
All the best, Mike
Click to expand...
That is why I asked if it actually boiled!
 
Boater Sam said:
Where is the temperature sender screwed in, the cylinder head, the thermostat housing or the heat exchanger/exhaust manifold?

If its in the engine I would bet its either 1/2" or 3/8" BSP.

If its in the heat exchanger it could be anything depending on the maker of the casting.
Click to expand...
It’s just below the thermostat housing into the engine
 
Could I point out that if the temperature gauge is an old car one then usually they had a voltage regulator in the supply to the gauge. If it was to be connected directly to 12v it would read too high..................
I use a a cheap variable voltage chip in the supply to the gauge and then can set the temperature so that it reads correctly.
 
mikeakc said:
Thank you everyone for the input here.

Having done some various investigations this weekend with a more mechanically minded friend than myself I have made some progress on this one! It turns out I was reading the temperature with my laser thermometer in a silly place (on the exhaust gasket which, apparently, will always be effing hot!) we run the temperature up to the point where the thermostat kicked in and saw a change in flow within the header tank so I am now confident that the thermostat is working as it should. With the header tank cap off we then let the engine hit 97° on the gauge and the water within the header tank was still cool enough to dip your finger in.

The conclusion was that the sender and or gauge are faulty or are not matched (i.e. have different resistances).

My next (and hopefully final) question is whether anybody knows the thread size of the temperature sender on a BMC 2.2?!

I will be aiming to replace both the gauge and the sender in one hit to rule out any compatibility issues. if anybody could recommend a matched pair which would fit my engine and 52 mm gauge cut out then I would be most grateful and also very impressed!!

I have already learnt a heck of a lot about diagnosing engines from this thread so thank you all for your input regardless of whether it was applicable to this situation or not.
All the best, Mike
Click to expand...
On my "spare " BMC 2.5 head the thread seems to be 3/8 BSP (19 TPI). The gauges in the ASAP catalogue are 3/8 NPT
(18 TPI) they will sort of fit or if you are religious you will need an adapter.
jim
 
Boater Sam said:
Could I point out that if the temperature gauge is an old car one then usually they had a voltage regulator in the supply to the gauge. If it was to be connected directly to 12v it would read too high..................
I use a a cheap variable voltage chip in the supply to the gauge and then can set the temperature so that it reads correctly.
Click to expand...
You could try putting two or three diodes in series with the positive feed to the gauge, the right way round of course, to drop 1.4V to 1.9V and may bring you back into calibration. It will still read higher as the battery voltage rises with the engine running though.

3/8" BSP sounds doable for the sensor.
 
Final update on this one - it's now solved. The issue was that the gauge and sender were not matched in terms of their resistance (one was Euro, one was US). I solved this by purchasing a Durite sender and gauge as a pack from Calcutt Boats. They also provided a thread adapter for the engine block. I made an utter balls up of fitting it - I thought the sender should screw all the way through the adapter so I started drilling it out with a larger bit. Then I purchased another sender which was the wrong resistance. Complete shambles. In the end I fitted the original kit supplied by Calcutt which I had damaged somewhat, but my faffing didn't affect the seal or fit so I was lucky. It's all cinched up and now reading a steady 75 when running at comfy revs, so I'm very happy! Cheers for all the advice.
 
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