Run a BB at 160??

DocDirk · #1 (**permalink**) 05-13-2009, 03:45 PM

Dropped my cobra off for chassis dyno tuning this week and was chatting with the owner about the cooling system. He's built many high performance street and race cars and told me that if carbureted, this engine needs to have a 160 Tstat and the fan trigger sensor set at 160 also, and run at 160 in cool weather, 185-190 in blazing hot weather (which we get a LOT of during the summer around central California). He says at 200+ engine temps the runners get hot enough to affect the atomization quality of the air/fuel mixture and make the car run poorly, that higher temp running works best for EFI engines.

Then again I've read posts here that say cool running hurts an engine, AND I'm wondering if having the fan work ALL the time is really any help, especially when on the road at speed. Right now I'm planning a 195 fan trigger though a 180 is available for that, and I have a 180 Tstat in place.

Man...if I ever graduate from the school of cobra/auto engineering I think I'll have a minor in confusion!

Regards!

Dirk

FWB · #2 (**permalink**) 05-13-2009, 04:08 PM

Quote:

Originally Posted by DocDirk

Dropped my cobra off for chassis dyno tuning this week and was chatting with the owner about the cooling system. He's built many high performance street and race cars and told me that if carbureted, this engine needs to have a 160 Tstat and the fan trigger sensor set at 160 also, and run at 160 in cool weather, 185-190 in blazing hot weather (which we get a LOT of during the summer around central California). He says at 200+ engine temps the runners get hot enough to affect the atomization quality of the air/fuel mixture and make the car run poorly, that higher temp running works best for EFI engines.

Then again I've read posts here that say cool running hurts an engine, AND I'm wondering if having the fan work ALL the time is really any help, especially when on the road at speed. Right now I'm planning a 195 fan trigger though a 180 is available for that, and I have a 180 Tstat in place.

Man...if I ever graduate from the school of cobra/auto engineering I think I'll have a minor in confusion!

Regards!

Dirk

he's scaring me....the t-stat temp rating is when it opens not how hot the engine will run. yes an EFI car will like the higher temp but yours has a carburetor. and you are correct the fan will make the engine run too cool at highway speeds, mine did, it would drop to 140 on the highway.
personally i think the t-stat you should start with, being i know some details about your car, is the 160 deg. however you may want to go to the 180, but i would wait to see. your climate is generally hotter than mine here, some nights its cool here and the higher rated t-stat is a better balance for me.
ignition timing and the quality of the fuel will also affect engine temp, so there will be more learning curve ahead on what your motor likes. if the 180 is in there now leave it in, isn't the fan sensor adjustable?

DocDirk · #3 (**permalink**) 05-13-2009, 04:25 PM

Haha, why didn't I think of that? Great tip Fred, no the temp sensor is static but of course I could put in a variable / adjustable sensor and crank it up or down according to whether I am driving in 50 deg coastal weather or 110 degree inland valley delight! Yes, thanks that was a great suggestion!

Dirk

mr0077 · #4 (**permalink**) 05-13-2009, 05:11 PM

Your engine guy is wrong, you want that motor to run at or above 180F. The T-stat is the minimum temp it will run at, so if you put in a 160 T-stat and it wants to run cooler, it will hover around 160, but if it wants to run hotter, it will. Running it cold is hard on a street motor, and I doubt if your 533 will stay at 160 anyway.
On the fan, you shouldn't need it all the time, put in a fan temp switch set for 180 or higher

Frank Messina · #5 (**permalink**) 05-13-2009, 05:23 PM

Doc,
Everything FWB said X2, plus an aluminum headed engine is going to take a bit more temperature (even up to 200°) to make best power and still be safe from detonation. An iron headed engine on the other hand retains more heat and is more susceptible to detonation if exposed to elevated operating temps for very long. If for some reason you ever do change the thermostat, test it on the stove in a pot of water first to verify the opening point. I've found that some 180° t-stats opened between 192 - 195°. Ford Motorcraft parts generally have been right on the money. I think your 180° is perfect. FWIW
Frank

Mike Braatz · #6 (**permalink**) 05-13-2009, 05:57 PM

You guys seem to have have cleared up that issue --what is the max. temp. you can run without damaging the engine??

bobcowan · #7 (**permalink**) 05-13-2009, 07:25 PM

There are a number of facters to consider here. If you listen to your engine guy, he's worried about heat in the intake manifold. I havn't worked with a BB Lima motor in so long, I'm not sure about that. It's an interesting theory, though. Everyone knows that cooler air makes more power.

A few well designed studies have shown that coolant temps below 160* will cause increase cylinder wall wear. But that means you'll only get 100K miles instead of 150K.

Oil should definatly be hotter than 160*, and probably closer to 200*. Oil temp tends to be pretty close to water temp.

As said above, the thermostat only controls minimum temperature, not max or operating temp. As the rpm's and ambient temps rise, so will the coolant temps.

The fan should not run all the time. There's no need and no point. The turn off point should be 5-10* cooler than the turn on point. With a 160* thermostat, I'd have it come on at 170, off at 165.

Dependin on the fan, it only moves air at about 30-40mph. If you're traveling at 50mph, you're moving more air through the core than the fan will. Put an over ride switch in the dash so you can turn the fan off while traveling down the highway.

I think it would be a struggle to keep a BB at 160* on a warm day in traffic. A by product of HP is heat. More HP = more heat. In the winter on the highway, I think it will be a struggle to get it above 180*. But, that's the whole point of a thermostat and a huge radiator - aiming for stability.

Here's what I would do. Use a 180* thermostat for the coolant. Use a 195/185* fan switch. To address the original intake manifold issue, I would have the bottom of the manifold ceramic coated to block heat transfer. But leave the top alone, or simply painted. You want any excess heat to dissapate through the top. Drive it around for a while. If it gets too hot, then change the thermostat and fan switch.