running hot on freeway

[Jules Dielen]

running out of ideas here, so asking the group for input.

My freshly rebuilt 1957 1600S is running hot on the freeway. It has approx 1500 miles on a standard setup, new Mahle pistons/cylinders, zenith carbs with super venturis/jets. Nothing fancy as i wanted reliability. It's running 250F on the freeway at a constant 70-80mph, 3500-3800rpm. In city driving it stays at a steady 190, it really only gets hot on the freeway.

I installed a new aluminum oil cooler and a 28 blade fan. I changed the distributor with a different one (tested good). Checked timing multiple times, all ok. All the engine tin is in place and the engine bay seal is new and sealing well. The combo gauge was rebuilt and I used the sender it came with from PAS. I double checked the oil temp with a fryer thermometer a few times and the gauge is spot on, the oil is really 250.

I dislike driving my car at this point, can't be good for durability.

Any thoughts/ ideas?

[Dan Epperly]

running out of ideas here, so asking the group for input.

My freshly rebuilt 1957 1600S is running hot on the freeway. It has approx 1500 miles on a standard setup, new Mahle pistons/cylinders, zenith carbs with super venturis/jets. Nothing fancy as i wanted reliability. It's running 250F on the freeway at a constant 70-80mph, 3500-3800rpm. In city driving it stays at a steady 190, it really only gets hot on the freeway.

I installed a new aluminum oil cooler and a 28 blade fan. I changed the distributor with a different one (tested good). Checked timing multiple times, all ok. All the engine tin is in place and the engine bay seal is new and sealing well. The combo gauge was rebuilt and I used the sender it came with from PAS. I double checked the oil temp with a fryer thermometer a few times and the gauge is spot on, the oil is really 250.

I dislike driving my car at this point, can't be good for durability.

Any thoughts/ ideas?

Stuck pressure relief valve?
Crap blocking the shroud either at the entrance or in, like a rag or piece of paper?
Belt tension too loose?

[David Jones]

Jules, try running 10/30 synthetic oil like Mobil 1. It will run cooler because it picks up and sheds heat better than conventional oil. It also can withstand higher than 250*F before it starts to oxidize. Conventional oils start to oxidize at 250*F. Mobil 1 from experience will run 300*F without smelling burnt.

[C J Murray]

Is the timing at full advance correct? Not enough advance causes heat.

250* on long runs of 70-80mph is not real bad. It takes around 210* to boil off the moisture in the oil and you have to go pretty high into the 300s to damage the oil.

[David Jones]

CJ, I have to disagree on max oil temp for conventional oil. I once ran a national at Road America and spent most of the race in a 13 car draft. My oil temp gauge only went to 270 and the needle was past that point. The engine had fresh conventional oil that weekend and after that race it smelled burnt. Never had that problem with synthetic and I ran a lot of races in the draft with oil temps over 275 and close to 300. By the way the company I once worked for in Chicago made analyzers for the petrochemical industry and I worked in R&D so I did learn a few things about oil which helped me with my racing.
Disclaimer, I do not use synthetic in my street cars any more (except the boxster) as they all run under 250*F no matter what the outside air temp so I now use shell Rotella which seems to be more than adequate even at plus 70 mph (just a little bit over 70) on hot days on the freeway.

[Jules Dielen]

thank you gents. I am running 20W50 brad penn (phoenix, AZ heat). I will try mobil 1 with a lower viscosity. There is nothing blocking the air flow from the fan, i've been in there a few times already . Pressure relief valve is one i did not think to check.

I am running a rebuilt 050, fresh off the test stand with graph. I had a BR18 on there before and it did exactly the same thing.

None of my other 356s run anything over 1/2 on the gauge at any time (never on the track, mostly just cruising and not pushing it to the limits), odd this one goes that high and it's not even warm here (mid 80s). I just don't like the gauge leaning toward the 3/4 mark on the gauge.

[Edwin Ek]

It does take a few miles for the engine to break in- running hot while that happens is not unheard of. Nonetheless I would want to take steps like you are.

[Jules Dielen]

I can see that Edwin, I just want to break it in, not break it period

[C J Murray]

300+ for synthetic, maybe 275* for conventional oil. Running around 180* all the time is as bad as running hot.

Most of the thinner Mobil 1 oils are lacking enough ZDDP.

What is the actual timing number at full advance? You should try it at 36* if it is less than that now. The idle timing is relatively unimportant, get the full advance number correct.

[David Jones]

Jules, Mobil 1 15/50 (1300 ppm) has the most ZDDP and both 10/30 and 10/40 high mileage have 1100 ppm so should work well. My pick would be the 10/40 especially in Arizona. Used to be at least 1200 ppm was considered safe but todays oils are so much better than even 10 years ago I would have no qualms running any one of them.

[Jules Dielen]

great, and I switched all my cars to brad penn because of the high ZDDP....

advance is 34 at 3000rpm, flat from that point on.

[Vic Skirmants]

Jules; the 1957 engine has a small oil pump; can't compare temps to a large-pump engine.

[Jules Dielen]

Vic, it does have the small pump, but so does my pre A and it does not run hot (temp sensor in the dip stick tube). Does the lower oil flow have that much of an impact on temp? And wouldn't it then always run hotter, not just on the freeway? Pressure is good, even at 250F. Small pump, no oil pressure light at idle!!

the 57 also has the temp sensor in the 3rd piece vs in the junction block on top like later engines have. That is partly why i carry the fryer thermometer with me.

[Greg Bryan]

How are you measuring the temp - the gauges are notoriously inaccurate? Did you replace the temp sensor during the rebuild?
You can check the temps in various places with an electronic temp scanner.

[Jules Dielen]

the gauge and sender were both calibrated as a pair when i had the gauge rebuilt by Palo Alto. Both were installed when this engine went into the car.

I manually compare the temp by sticking a fryer thermometer into the dip stick tube, so the end is dipped into the oil. I tested the fryer thermometer in boiling water, so it is accurate as well. The fryer thermometer is spot on with what the gauge reads (i see the gauge while checking the thermometer in the engine bay so i can compare). They were both at 240F with the engine idling after a freeway drive.

I am not a fan of infrared temp guns as they read the surface temp only, that is not what the oil temp sender reads.