Jupiter Overheating

[Kevin Lord]

On my Jupiter EISA 453 Runs, good most of the time, Cleaned radiator, reset timing. Temp. gauge checked and reading o.k. On recent run outside temp.28%+ driving hard over hills and motorway Temp never exceded 80deg. Stopped for lunch and a slower drive home, motor missed briefly then ran HOT, but still ran o.k. Head gaskett or what. Suggestions welcome.

[Keith Andrews]

The most common issues Hot runing :
1/Blocked radiator cores..clean/ flush doesnt mean its not blocked..to be sure remove headers and manually clean cores
2/Thermostat not opening or opening in incorrect range or not opening all the way up..replace
3/Runing lean..intake leak, butterfly bushes..spray a little engine start to these parts and note any changes in rpm /vaccuum.
4/Cracked head or blown gasket...Get a HC check on the Radiator..most workshops do this for free
It is not uncommon to get combinations of these

U mention running hard and doing when slower running.....
Partly blockewd radiator...does it get to hot when idling and around town?


.

[Keith Clements]

Check timing. Distributor could have moved, spring could have come off.

[Mike Allfrey]

G'dday From The (Yet Again) Sunny South,

Now, this is going to stir the pot a bit!

My Jupiter has bee running at about 80 to 90 degrees centigrade (%?) in warm weather conditions since the Solex carburettors have been installed. A couple of weeks ago, I took the car to our carburettor specialist to try different jetting in an endeavour to clean up the sparking plugs which were black and sooty.

The main jets were reduced from 120s to 105s and the engine ran much cleaner.

Now, here is the conumdrum - in ambient temperatures (in shade) of 36 degrees centigrade, and while in very heavy traffic and with 18 sets of traffic lights in one street (virtually all on red as approached), the temperature gauge never lifted more than needle thickness above 75 degrees. A burst along the freeway did not affect the engine's temperature. So, work that out. maybe running overly rich on modern petrol affects the engine's running temperature?

A word of warning - if it is head gasket, remember that the only time a Jowett fires up instantly is when one cylinder is full of water! Something has to give, and it is usually the crankcase. If a head gasket is suspected, it is wise to use the starting handle to turn the engine before starting. If it feels solid, either 'lean' on the handle to squeeze the water past the piston rings, or, remove the sparking plugs and let the starter motor do the work. Crankcases are too valuable to loose this way!

Regards,

Mike Allfrey.

[Mike Allfrey]

Dear Pat,

I have always felt that the Zeniths were fairly low on the list of useful carburettors!

The prime reason for fitting the Solexes was because the float to needle valve relationship was better. The other reason was because the throttle bodies are water heated and there is no icing concern at all.

I have no idea at present what the exhaust analysis was, but will try to find out sometime.

Meanwhile the engine performs like a turbine with no flatspots and idles at an easy 400 erpm. That never happened with the Zeniths - either 30 VM-5 or 30 VM, or 30 VIG sets. The Solex pair worked well straight from the reconditioner, but ran a little rich - hence the re-jetting.

We shall see!

Mike Allfrey.

[Keith Andrews]

So, work that out. maybe running overly rich on modern petrol affects the engine's running temperature?

The BTU and pacific gravity (SG) of the new fuels are little different...
Works like this...methanol has lower SG but has a far higher energy, so on has to 'pump' more fuel into the mixture (bigger jets)

Going from old to new fuel doesnt normally require any major changes IF the jets are correct in the 1st place
If the jets are way off, thu no far enough to seriously have any effect, the change of fuel can just be enough to tip the scales into messing plugs and running hot.

[Forumadmin]

I will have to get the text books out; but something at the back of my mind says that the complex relationship between jet size, mixture ratio, combustion temperature, gas flow, power, timing (both valve and ignition) and water temperature is not as simple as we may think. I have definite experience that over advanced engines overheat; contrary to the belief that retarding overheats (hence advancing cools). There are probably maxima and minima curves which do not coincide at the stoichiometric point. The clue may be the flame speed. If the mixture is weakened the flame speed may decrease, thus retarding the engine, which as I said above may actually cool the engine!

Taken from Wikipedia....
A stoichiometric mixture unfortunately burns very hot and can damage engine components if the engine is placed under high load at this fuel air mixture.

So does that mean it burns cooler either side of the SP? It is 40 years since I did the theory and need to refresh myself!!!

[Keith Andrews]

but something at the back of my mind says that the complex relationship between jet size, mixture ratio, combustion temperature, gas flow, power, timing (both valve and ignition) and water temperature is not as simple as we may think

Correct....
Yes the principle explained is over simplified....
If timing, DC, octane and other parameters remain correct and constant, as was described in the case above...the issue is simply re jetting

To Many ppl get so tied up in the complexities of the variables looking for fancy solns when ,

I took the car to our carburettor specialist

, going from the results with test driving...
diagnosed the issue after a few checks and questions, simply and quickly.

Never under estimate the old school skill of reading plugs correctly on non computerised engines

[Keith Andrews]

Taken from Wikipedia....
A stoichiometric mixture unfortunately burns very hot and can damage engine components if the engine is placed under high load at this fuel air mixture.

So does that mean it burns cooler either side of the SP? !

Yes...that is where advance, octane, knock, DC etc comes in