Temp question at higher speeds

[Andrew S]

Quick questions guys, my temp is running at juts under half at 70 ish and when on back roads she is dropping to a third. Before the engine rebuild, 2500 miles ago, I had fitted an 82 deg stat and a 20psi cap. I was advised by the Stag place, that it would be kinder to the engine to have a 13ib cap and they have fitted a 76 stat as standard.

I would have expected the running temp at higher speed to be very lower as the radiator would be open the whole time. In other words one stage from not having a stat in at all.

I was under the impression that maybe I was running weak on mixture and so enrichend the fuel and am running at 5%.

So my question is or maybe my questions are:-

• Will temp reading be lower if I have an 82 deg stat fitted again?
• Does having a 13lb cap also raise the temp?
• what is the ideal mixture percentage so that I can reset it up as its not as good as it used to be on mpg on a run as before the rebuild?

My Stag is a manual MK2 and I have timing set at 14 degs for unleaded as it goes better than at 12degs

The car does not over heat at all and will only go up to the 1st white dot on the temp gauge at its warmest. My engine never moved about the 1/4 1/3 position before it was rebuilt, so this is why I am presuming that its the set up

Any comments much appreciated

Andrew

[Thurlo Squire]

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Hi Andrew

Personally I don't see the benefit of running with a 76 degree stat. 80 to 90 degrees is considered the normal operating temperature for the Stag and so 76 degrees will open too early and slow the car from getting up to normal operating temperature. Not a massive issue in the current weather but will have more impact in the winter.

Just because the stat is open and the radiator is getting lots of airflow at speed does not mean your temperature should run lower. On the converse the engine is likely to run hotter when running at speed as it is working harder and the sender unit for the gauge is in the engine..

My own car tends to run at around 85 degrees on normal driving rising to around 90 degrees (Auxiliary capillary gauge fitted) when in traffic or high speed running. This shows as close to the right of the E of TEMP on the standerd gauge when running at about 85 degrees and then just touching the M when at around 90 degrees.

I am running the standard set up of 82 degree stat and 20lb cap and all is fine. I would change your stat for sure.

As regards the mixture then I would say 5% is too high. Normal setting is in the range 2 - 4% so I would weaken it down a touch.

Nigel

[Andrew S]

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Thanks Nigel

I think this is more of a case that my engine temp reading was always stuck at about a 1/3 however I drove it and now that all the parts have been replaced and I know the rad is fine, then it has to point to one of these components.

I agree about changing the stats and most probably will do shortly.

My mixture was previously set at 3.5% and at the same time as I changed the timing to 14degs from 12 degs and enriched the mixture to 5% it went well. The reason why I did this was due to lack of pull in the car and now it has plenty oftorque and even better now that the engine has more mileage since rebuild.

Could some temp sender units read higher than others perhaps?

Its not an issue as she does not over heat, but I have been used to seeing the lower reading

Cheers

Andrew

[stustag]

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Hi Andrew

I would recommend you change to 82 degree thermostat and also change the temp sensor as it may not be reading correctly.

The reading you get at 70 mph on a normal day (15 degree) is what I get however when it is like today (22 + Degree) mine runs with the point of the needle on the first small dot.

I find it funny that most of us worry about the engine running to hot not to cold

5% is too high on the mixture I would recommend 2.2 -3.5% and make sure the carbs are balanced and the dash pot oil level is correct with resistance being felt on the damper with 6mm clearance. This will give you great performance and smooth carburetion throughout the rev range.

Stuart

[Andrew S]

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Thanks Stuart

I may well do the mixture tomorrow as its poor on a run. I always got 28 to 30 on a run at say 70-75 and being manual, it wasn't problem. At the time my fuel was set at 3.5% and timing was at 12 degs and it had no pull up hills on a long incline. It wasn't long ago tat I was down in Devon and with some of those hills and with kids in the back, I could have run up those hills quicker and I had to change gear to get the revs / pull. Also at the time noticing that the temp was higher than before, I just presume it was running weak. That's why I put it up to 5% and the timing to 14 and no problem.

I find it encouraging that she should run well at under 3.5% and will tune her again after using air flow meter to balance air intake.

My reading as you say is the same as yours at 70mph being on the first dot on temp gauge and therefore nothing to worry about and also confirms that it is not connected to fuel mixture

I will get another sender and go for the 82 deg stat

I am happier with the 13lb rad bottle cap rather than the 20lb and presume that this does not make any difference to high speed running temps? I understand that the reason we are supposed to use a 20lb cap is that it takes longer to boil than a 13lb when under pressure. I may be wrong

Thanks for the reassurance

Cheers

Andrew

[Thurlo Squire]

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Andrew S wrote:

I am happier with the 13lb rad bottle cap rather than the 20lb and presume that this does not make any difference to high speed running temps? I understand that the reason we are supposed to use a 20lb cap is that it takes longer to boil than a 13lb when under pressure. I may be wrong

Andrew

That's right. Running with a 13lb cap won't affect the temperature.

Nigel

[Andrew S]

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Thanks Nigel

Andrew