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Hey all, I have a fresh built 391 in a 72 Newell Motor Coach with a Holley Sniper EFI and Hyperspark Ignition. Ignition timing is currently set to 10 degrees and I'm about to adjust to 5 in hopes of it helping. It only overheats when sitting idle. New fan cluch, new custom shroud, radiator was cleaned. I'm thinking Ignition timing and maybe the radiator cap is the wrong psi. Any 391 guys out there that can help? I've made 4 trips in this Newell since I restored all of it and it really only gets hot when sitting idle after a long drive. What should I be looking at as far an Ignition curve?
Some of this is different from my events but the cure was a new 2765 Hayden clutch a 7 blade fan C9ZE with shroud a 190 thermo and a high efficiency triple pass new radiator. I tried almost everything one the past fe years. Tis combo has kept engine temps at 180-200. ITs a 390 FE at 15* and 7k-8k' on 6% grades. Waited in the choke and puke for 10 minutes at idle ambient was 92*mol with no heat rise over 200. FWIW
 

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… a 190 thermo … Tis combo has kept engine temps at 180-200.
So, you may need a new temperature gauge? A 190°F rated thermostat only begins to crack open at the rated temperature. The stable operating temperature (control range of the thermostat) should be within 5 to 15° above that, e.g., 195° minimum to 210°F maximum (in a properly operating system) in your case, unless 190 was a typo?

IMO, there is no need to run temperatures that high, with exceptions for emissions schemes, or short-trip vehicles to quickly burn-off oil contaminates, or very cold climates where the heater needs to work better. Power and engine wear both benefit from temperatures held to ~175° and below, as well as reduced chance of fuel boiling (ethanol blends), vapor lock, etc. Power applications that can hold temperatures, such as offshore racing boats, commonly use 140°F as their target.
 

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Sure, but we have beat this horse beyond death repeatedly in the past, using studies and controlled lab tests, as well as teardown data from large organizations such as AERA, along with user real-world results and side-effects. The wear profile is a curve, with greater wear (corrosive at lower and abrasive at higher) when too cold or too hot, and a sweet spot right in that range. Power and reliability are the big wins, while economy is desired but not the highest priority here, nor is the question of whether to rebuild after 22 years or 25. Many other factors weigh-in for us end-users beyond strictly wear, from heat-related seal life to coil failures to wiring breakdown. Rather than repeating existing info, I can do a search for some of those threads for you.

However, I do not wish to hijack the thread from the OP's issues, in which he would likely be very happy trading more regular oil changes to avoid corrosive wear, for solutions to heat accumulation in a heavy duty RV application. I certainly would, considering a $10 thermostat could ease his life considerably and avoid the costs of more cooling upgrades. Besides, any further investment would wipe-out any potential savings in long-term wear, if it hasn't already. ;)
 

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Discussion Starter · #25 ·
Hey everyone, sorry for the delay in response. I have been trying to dig myself out from underneath all the work I have lately. Anyhow, I have taken alot of consideration in just about everything that has been mentioned. I flushed the coolant, which btw, the radiator was professionally cleaned and fins straightened before this new engine ever started up. I put in a coolant overflow resevoir and built a radiator to chassis seal to eliminate hot air going back into the front of the radiator. I replaced the fan clutch with another new one. I set the Holley dual spark distributor with a timing light to 10 degrees and I tuned the ignition timing to be 15 degrees at idle. See pics below. I also got the build sheet from the engine guy and found the specs on the cam which I've posted below. I'll be doing some test driving this week.

Grille Window Fixture Wood Automotive exterior


Fixture Rectangle Wood Window Window blind


Motor vehicle Light Automotive design Automotive fuel system Automotive exterior


Font Line Parallel Pattern Number
 
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