radiator cap pressure

[Art Burtt]

Don, What pressure should my radiator cap be? Engine builder
suggested running without a thermostat.What's your opinion on that?
Art

[dscott]

Art, I run a 15 or 16 lb cap. You do need to run a thermostat. It maintains proper engine temp. Without one you may run too cool and never get the engine to operating temp.
Don

[Ken Greene]

with an answer like that from the engine builder i would question your choice in the builder.
And i agree with Don

[Art Burtt]

Ken,
Engine Factory here in NJ????

[mr0077]

Yeah, you need to run a T-stat on the street...lets you get to operating temp ASAP, and maintains pressure flow through the block and heads.

[scottj]

Use the highest rated cap your radiator will allow. For a typical performance aluminum radiator that would be a 22-24# cap, a racing radiator can use a 29-31# cap.

IF you must run a thermostat to maintain operating temp, the Robert Shaw high-flow thermostat is the least restrictive.

Scott

[mr0077]

If it is going to run hot or overheat, leaving the T-stat out won't make it run cooler, and can cause localized hot spots (steam pockets)...and if you don't have one, it will take forever to warm up. Run a thermostat. If it is for race purposes, at least put a restrictor in place of the t-stat, for pressure flow in the motor.

[K.Wilson]

Running without a thermostat or a calibrated flow restrictor is probably the single most damaging thing you can do to an engine with the exception of running without oil or coolant!
Keith

[Jack21]

Ditto the above. Bad advice from an engine builder.

These street motors need to be at proper operating temperature to work properly. Run a 180 degree low restriction thermostat (like Robertshaw) year round.

The higher the pressure relief on the rad cap, the higher the coolant temp can go before boiling. But, the higher the stress loads (and life expectancy) on hoses and hose connections. I went with a 7 pound Stant cap, and so far (2 years & 12,000 miles) so good.

That being said, Cobras have notorious reputations for overheating so install the best cooling system components you can get. Griffin aluminum radiator. Pricey, but it does work well. Healthy electric fan properly mounted to its own bracket, with manual override. High flow water pump like the Edelbrock or comparible. If using March pulleys, use the Street Rod ratio, not the high performance ratio because it flows more coolant.

You'll thank yourself when you're stuck in Summer traffic and your Snake keeps its cool.

[Art Burtt]

called engine builder today,apparently I mis read info. I was to leave it out to facilitate coolant fill only then run 180-195 thermostat. I kinda thought the circulation would be so fast the radiator wouldn't get a chance to do it's job. That's why I asked the question. Thanks for all your help.

[scottj]

Leaving the thermostat (or restrictor) out won't cause the coolant to flow too fast through the radiator. Nobody even makes a water pump that will flow too fast. The faster you can flow the coolant the LESS likely you'll be to develope hot spots and steam pockets. That's why the makers of performance water pumps, like Edelbrock and Stewart, develope their pumps to flow as much as possible. And it is why they don't recommend underdrive pulleys or restrictors. It is also why the Robertshaw high-flow thermostat exists.

Leaving the thermostat out can cause it to run too cool though.

Putting one in can cause a race motor to melt down if it sticks shut, so many builders leave them out of race engines.

Scott

P.S. Running without a restrictor isn't damaging, but misinformation can be.

[mr0077]

The possibility of a failed T-stat is why it is replaced with a restrictor plate in most race motors...running without a restrictor CAN damage your motor...you're right about misinformation, though.

[bmalone]

Thank you, Mr0077. That is my setup. Works fantastic. Would not put a thermostat in if you paid me--but that is for my application and likely not right for most. I have avoided commenting since this post seems geared for SB's and a BB is a bit of a different situation.

BTW, I run a 16-18 Lb. cap.

[wizard]

Mine runs a little hot in traffic. No Thermostat. Picked up on an earlier thread about Edelbrock water pumps and became convinced that was the sloution. Jegs catalogue had restrictor plates next to the water pumps. Now I'm confused. Called Edelbrock. Explained my delema. Now this is a first rate company. Knowing that my credit card was at the ready, Edelbrock said put in the thermostat. Could have sold me a $250 pump. Didn't say why though, but Mr0077 gave me the final clue to the puzzle. "Pressure" Should have realized this from some heating and cooling applications I have at work. More pressure means a higher boiling point so you are less likely to have vapor pockets in the block. More liquid contact means more cooling. Having said all that, it's all theoretical until I install the thermostat that been sitting on my shelf for a year or more and prove it this weekend.

[scottj]

Cooling System Basics for Spark Ignition Engines SuperFlow Advanced Engine Technology Conference, December 7, 1992

Quote:
Coolant temperatures are not an accurate indicator of metal temperatures. The coolant's maximum temperature is it's pressure corrected vapor point. The metal can be several hundred degrees hotter than the adjacent coolant

Higher coolant flow will ALWAYS result in higher heat transfer. Coolant cannot absorb heat after it reaches it's pressure corrected vapor point.

Coolant flow has a direct relationship to area and an exponential relationship to pressure. Meaning that when you double the area of an orifice and maintain pressure the flow doubles, but when you double the pressure and maintain area the flow is only increased by 1.414 (the square root of 2). End Quote

Restrictors REDUCE the area, REDUCE the flow, and thereby REDUCE the coolants effectiveness in transferring heat. The result of this is INCREASED hotspots and steam pockets in the heads. Steam pockets ELIMINATE the coolants ability to transfer heat in that area, resulting in increased metal temperature and increased chance of detonation.

If you guys just want to feel good about 1950’s theories then continue stroking each other.

Dance lesson over. Scott

[petek]

"Higher coolant flow will ALWAYS result in higher heat transfer."

True up to the point that the flow becomes non-laminar and cavitation occurs. Right?

[mr0077]

Scott, do you have any salt and pepper for the crow I'm about to eat? I saw your last post and had written up this MIGHTY reply, but thought I'd a bit of quick research first...I found this site that has a lot of good info, and well respected...man, I hate to admit it, but...well okay for race purposes ONLY, then...you are right about the restrictors...see below, and surf the site, lotsa good info on cooling:
http://www.stewartcomponents.com/html/tech_support/
Thanks for the "nudge" to get me to edjumacate myself...I'm VERY surprised that these guys consistently recommend no T-stat and no restrictor (usually for race motors or major cooling problem set-ups). It apparently has to do with their pumps providing MUCH better flow...so, I slink off into the darkness...

[scottj]

Ken,

Where did you think I was getting this stuff? Actually I've been running Stewart pumps for years, they, and my engine builder changed my whole thinking on cooling.

Scott

edit: For street applications they recommend up to 35% overdrive on the pump and a Robertshaw stat... Flow, Flow, Flow.

[Art Burtt]

Minga!!! What a can of worms I opened. Too many engineers in this world, you're like the salesman who explained the whole theory
of electricity and how efficient it made the heater work, that a little old lady wanted to buy. After he was all done with his impressive oratory she asked "will it keep a little old lady warm"?
Guess I'll put in a thermostat and see how it goes. Enough already!!!