B18 B overheating

[Salop Farmer]

Ps forgot to mention but I had checked the operation of the thermostat and it was starting to open at 77 - 80 degrees and fully open soon after. And definitely the correct one for B18 engine. So am very puzzled !

[Juular]

Don't want this to sound like a stupid question, but where on the gauge does the needle sit?

When the factory gauge is out of the instrument panel you can see the temperatures marked out at the very top. 90C is actually quite far to the right, so it may look like it's running hot.

https://www.sw-em.com/temperature_gauge_notes.htm

On mine I find that as long as the needle is within the coloured green and white bands then it's within a normal range.

[Juular]

Here is where my Amazon gauge sits at a 'normal' temperature, measured with an IR thermometer at around 90C.

[Othen]

Originally Posted by Salop Farmer

I have driven around 500 miles in my rebuilt B18B engined 544. Most of the time the temp gauge reads between 87 and 90 degrees C. If I turn the heater control to cold the temperature climbs even higher. The B16 radiator and engine waterways are all clear, water pump and thermostat new and coolant free from air locks. The other day I decided to remove the ( Brookhouse) correct thermostat from its housing, top up the coolant and run the car on a 10 mile trip.I put the heater control to cold and observed the temp. gauge throughout the drive. The needle got up to around 70 degrees and pretty well stayed there except when climbing a long hill when it got up to about 82degrees. So I am suspecting a faulty thermostat!
Was wondering if others agree?

That sounds most logical. I’d suggest the next thing to do would be to test the thermostat, which only takes perhaps 10 minutes.



Addendum: I’ve just noticed from your later post that you have checked the thermostat, and it is okay. In that case I’d agree with Juular’s recent post - the gauge does look as if it in the hot region when running normally, my Amazon is much the same.

[Salop Farmer]

Thanks Juular that’s reassuring in a way cos that almost identical to where my needle sits with thermostat fitted. I had the low temp thermostat fitted (76 degree opening) and having checked my gauge for accuracy would have thought the needle would hover round the central greens section of the gauge. In traffic it can get into the last white section of the gauge (92 degrees) which I find slightly worrying as we’re not into the hot weather yet! Maybe I should just chill a bit! Haven’t been on more than 20 mile trips cos of this issue.

[142 Guy]

My following comments are based upon the assumption that you are using a 50:50 glycol:water coolant mix or something close to that. They are not valid for a high glycol mix which suppresses boil over and also causes higher operating temperatures because of reduced heat transfer.

My observations are as follows:
- if you have not vented coolant because of boiling then you have not overheated.
- My B20E thermostat starts opening around 82C and goes fully open around 90 C. The typical coolant operating temperature is pretty much 87 - 92 C when the car is moving / engine running around 2500 - 3000 RPM. On a hot day (30C), when I come to a long traffic light and the engine is idling the engine temperature gauge will creep up to 100C or slightly higher; but, that is primarily because the engine temperature gauge is at the back of the head and at idle the coolant flow drops off so the coolant at the back of the head runs up to 10C higher that the control point at the thermostat housing.
- If you open the heater valve the heater core inlet is at the back of the head. This increases flow through the head which tends to drop the temperature measured by the gauge because of increased flow. This is normal for the B18 / B20 engines.
- Opening your heater valve also provides some supplementary cooling. That would be more indicative of issues associated with marginal radiator capacity than a thermostat problem.

I think you are probably just fine. With the car in motion, an operating coolant temperature of 87 - 90 C would be be 'right on the money'. On hotter days, it would be normal for the temperature to creep up to 100C when you come to a stop with the engine idling.

I think your Brookhouse thermostat is just fine. An engine operating around 70C is too cool. On a really hot day (30+ C), if you start to find that with the car in motion that you are running closer to 100C then you may have a cooling problem; but, I suspect that cooling problem may be more related to a smallish radiator than the thermostat. Remember that above 90 C the thermostat is 100% open and the cooling system is in full flow mode. Any temperature rise above 90C is because of a lack of heat rejection by the radiator.

[Salop Farmer]

Thank you 142 Guy for your detailed response. I will refit a new thermostat ( to be sure) and keep an eye on the situation. Although B16 rad is on the small side for a B18 engine the water has never boiled over.