[Bronze66]

I'm finally getting the bugs worked out of my new motor. One of the main things was temp. It basically now runs around 170-175 under 85 degree outside temps. It will heat soak to 190+ in stop & stop city traffic. Then cool down when moving. I have 160 stat in it. Just wondering if it's running to cool to make the most efficient power? It will drop below 170 on cool nights. I've leaned the carbs out and boosted timing 14I,38T, 27 & 49w/vac at cruise with no adverse effects on temp. I could run a 170 stat. Which should boost the temps 10 degrees I'm assuming. Is 180-185 a better temp for power and combustion efficiency? CR is 9.3, compression is 160 all around. It does run very good. I'm just trying to squeak every mpg out of it as I can. Just something I'm playing with. Mileage did go up with the added timing and leanness.

[TransAm525]

If you want maximum mileage and efficiency, run a 195 degree thermostat. Remember, the thermostat does not control the maximum operating temperature of the engine, it only controls the minimum (when the thermostat starts opening) and will try to keep it there as long as the rest of the cooling system can support the demand. Take a look at the graph below for some more interesting info. I personally run a 180 in my 400 and pull around 17 mpg on the highway, and that's with a TH400 transmission and turning 3000 rpm.

[79TA455STROKED]

Also ,where are you taking your temp reading from?Taking it from the intake will give you a cooler reading then if you take it from the back of the heads.I bet it is about a 5-10 deg difference.I have my temp sensor in the back of one of the heads and my thermo for the electric fans in the intake.The fans are supposed to kick on at 195 but kick on a little later according to my gauge because my gauge is taking its reading from a hotter spot.

[Z Code 400]

We recorded our highest horsepower and torque on the dyno with the lowest coolant temperatures. I run 160° thermostats in all my cars. Here in central California, we see 32° in the winter and 104° in the summer and I find acceptable coolant temperatures for heater operation.

The other thing most people don't take into consideration is you don't have hot intake air in the dyno room!!!

We have also ran our tow vehicle over 100,000 miles (429 Ford) with a 160° thermostat, often runing as low as 170° at night, without any sludge or abnormal wear. We have disproven the 'cold engines wear faster' myth time and again, with everything from Flathead Fords to countless numbers of street engines.

Originally Posted by David Reher

"Our dyno and track tests have repeatedly shown that a drag racing engine runs best and produces the most horsepower and torque with thin, synthetic oils and cold water...Some racers believe that a warm engine makes more power than a cold engine. Others think that a warm engine is more consistent. In fact, heat is the enemy of performance. A motor will make more power if you run it cold - and it can still be consistent. Use synthetic oil and run your engine as cool as you can."

[TransAm525]

Bronze 66 is looking to pull out every bit of economy from the engine, not power. All newer cars run 195-210 degrees for emissions and economy reasons. I agree lower coolant temperatures will produce more power, but I'll have to disagree on the engine wear not increasing with the lower temperatures. Running an engine at 160 degrees and below over the life of the engine will have accelerated wear compared to an engine running 180 degrees and above. Listen to any new GM engine and you'll hear the pistons and rods clattering away until the engine warms up, the same goes for some cars using certain forged pistons and engines with solid lifter cams (valvetrain clatter when cold). I'm sure your experience will agree that if the engine is built to run a low temp cooling system (built with tighter tolerances), then the effects with running colder engines might not surface since the engine was built in a manner that the tolerances will be perfect at the lower temperatures already.

Another downfall to running a colder temp is specifically what Bronze 66 doesn't want--poor economy due to incomplete fuel atomization when running a carbureted engine. There is a long list of things he can do to increase economy, but running a 195 degree thermostat with the manifold heat crossover open will provide optimal economy, but at the expense of some power. On many of the newer fuel injected cars, running a 160 degree or less coolant temperature will prevent the engine from entering closed loop mode, thus causing the engine to run at the richer default setting constantly.

[Will]

Addressing ONLY the wear issue -

Originally Posted by TransAm525

... All newer cars run 195-210 degrees for emissions and economy reasons. ... Running an engine at 160 degrees and below over the life of the engine will have accelerated wear compared to an engine running 180 degrees and above. ....

What is your actual evidence of this?

Because saying:

Originally Posted by TransAm525

Listen to any new GM engine and you'll hear the pistons and rods clattering away until the engine warms up, the same goes for some cars using certain forged pistons and engines with solid lifter cams (valvetrain clatter when cold). I'm sure your experience will agree that if the engine is built to run a low temp cooling system (built with tighter tolerances), then the effects with running colder engines might not surface since the engine was built in a manner that the tolerances will be perfect at the lower temperatures already.

Doesn't really say anything about running an older Pontiac at lower engine temps.

If you are claiming that the new engines clatter because they are built with loose tolerances in order to accomodate high operating temps and thus greater piston expansion that makes sense but I don't see how it has anything at all to do with long term engine wear. Please explain, I must be missing something.


Furthermore, unless you're running really loose clearances, I've never heard a street/strip Pontiac that had significant clatter at startup. Even my 440, with .007" piston-bore clearance and a solid roller cam wasn't particularly noisy at startup.

.007" was not the intended clearance, but after a bearing failure in the first 1000 miles of running the cylinders were honed an additional .003" to clean them up.

Finally, I find it hard to believe that 20 degrees difference in coolant temp is going to make a significant difference to piston-bore clearances in a fully warmed up and running engine.

I do agree that running the engine hotter will enhance economy, allowing leaner mixtures and better fuel atomization. It also helps with emissions, which is the primary reason modern cars run hotter. Fuel atomization is a distant secondary factor in a modern car - fuel injection, ya know.

As for my own experience in this matter, I can only offer up the 6-cylinder in my Nova which ran with a 170 degree thermostat for 80,000 miles from time of full rebuild. That engine was run hard and put away wet, and driven daily for about 5 years and still ran like a top and didn't burn any more oil when I sold the car. I don't suppose 80K is long enough to really count as a long-term test, but most people won't put 80K on their Pontiacs in the next 10 years.

[smagnotti]

the main thing concern for running on the cool side of things in street car is that your oil temp still needs to get above 212 degrees to boil off moisture and combustion acids.
My 455 has no problem hitting that temp on a cool day(65 degrees and dependant on rpm) but my 400 does if I run less tha a 180 T-stat!

[Z Code 400]

TransAm525,

Regardless of coolant temperature, a forged piston will expand after just a few minutes of run time. This was very evident in our 427 Ford with .007" piston to wall clearance. There was audible piston 'slap' for the first 45 seconds of run time after start up. The noise disappeared after that.

I agree with you that the open crossover will afford better atomization and that new cars (OBD III) will not go into closed loop below a certain temperature, but we have seen no measureable difference in fuel economy between 170° and 200° coolant temperatures during dyno testing, even running a fully warned up engine through a single gallon of fuel.

Let's examine the cylinder wall wear chart your provided. 50 hours at 50 mph would be roughly 2500 miles of driving. The chart indicated roughly 0.0055" of cylinder wall wear at 170° to 190° coolant temperatures and only about 0.0035" between 175° and 200° coolant temperatures.

Let's use the 0.0055" value and estimate cylinder wall wear over 75,000 miles. That would equate to approximately 0.165" cylinder wall wear over a 75,000 mile period. Yet, the 429 Ford in our tow vehicle ran a 'hollowed out' 160° thermostat that was open all the time. Coolant temperatures ranged from 140° (downhill at night) to a high of 185° (uphill under load) in the daytime. Average coolant temperatures were 165° to 170° for the life of this engine.

We pulled this engine to freshen it at a little over 100,000 miles and recorded less than .006" cylinder wall taper. We didn't bother to rebore the engine, since the wear was so minimal and even.

We ran the wrong oil too. That engine was broken in on Shell 20/50 Ashless/Dispersant Aviation Oil and we used nothing else for the life of the engine. The cam and lifters still looked decent on tear down, despite the lack of ZDDP...Robert

[Z Code 400]

Originally Posted by smagnotti

the main thing concern for running on the cool side of things in street car is that your oil temp still needs to get above 212 degrees to boil off moisture and combustion acids. My 455 has no problem hitting that temp on a cool day(65 degrees and dependant on rpm) but my 400 does if I run less tha a 180 T-stat!

Your 455's larger main journals are likely to generate more frictional heat than the smaller 3.00" journals on the 400.

Our 429 Ford tow vehicle recorded 210° to 220° oil temperatures at 170° coolant temps under load. On the other hand, the 427 in our race car always had oil temps 20° to 30° cooler than coolant temperatures. Even with the radiator partially blocked and showing 210° coolant temperature, the oil wouldn't get over 185° to 190° under load...Robert

[TransAm525]

Will,

It's a combination of what Smagnottie and I both said. Reducing the engine temperatures will cause the oil to sludge up more than the higher engine temperatures. Lower temperatures will also cause incomplete fuel atomization on carburated engines. This is why the factory either installed a heat crossover or a coolant channel below the carburetor. With the incomplete fuel atomization comes all sorts of problems, such as increase cylinder wall wear and fuel/oil contamination to name a couple. The cylinder bores and the pistons rely on the heat generated from the combustion process for proper metal expansion. The pistons will grow in size while the cylinders will do the same. As this happens, the tolerances start to close up. When you run the engine cooler than designed, the tolerances don't close up as much and the results (in addition to the fuel atomization issue) are pistons that rock more in their bores and solid valvetrain parts that clatter more unless specifically adjusted to compensate for the lower temps.

In summary, the increased wear is minimal, but it is there. On a race engine that only sees a few thousand miles a year between tear-downs, you're not going to really see the effects. However, on an engine with 200,000+ miles the effects will become more apparent. The graph I attached is from a long article conducted by a university a few years ago. I wish I could remember the website, but it's been a while and I don't have the link anymore (I just saved the graph).

[sixt8bird]

Originally Posted by TransAm525

Will,

It's a combination of what Smagnottie and I both said. Reducing the engine temperatures will cause the oil to sludge up more than the higher engine temperatures. Lower temperatures will also cause incomplete fuel atomization on carburated engines. This is why the factory either installed a heat crossover or a coolant channel below the carburetor. With the incomplete fuel atomization comes all sorts of problems, such as increase cylinder wall wear and fuel/oil contamination to name a couple. The cylinder bores and the pistons rely on the heat generated from the combustion process for proper metal expansion. The pistons will grow in size while the cylinders will do the same. As this happens, the tolerances start to close up. When you run the engine cooler than designed, the tolerances don't close up as much and the results (in addition to the fuel atomization issue) are pistons that rock more in their bores and solid valvetrain parts that clatter more unless specifically adjusted to compensate for the lower temps.

In summary, the increased wear is minimal, but it is there. On a race engine that only sees a few thousand miles a year between tear-downs, you're not going to really see the effects. However, on an engine with 200,000+ miles the effects will become more apparent. The graph I attached is from a long article conducted by a university a few years ago. I wish I could remember the website, but it's been a while and I don't have the link anymore (I just saved the graph).

I call BS on the sludge build up. Im 100 % in agreement with Z code 400. I live in the NW and temps are from 30 degs in winter and 80s-90s in the summer. All I run are 160 stats and my Pontiacs run at about 170-175 in the summer. I had 270,000 miles on a 350 Pontiac that I built in 1980 and drove it daily for 20 years. I actually ended up selling the engine and it looked like a brand new engine when the intake and valve covers were pulled off. If you havent heard, WA state gets alot of rain which also means 100% humidity. Wheres the sludge? I also run a 400 with non ported heads that I have had since 1991 and this car is beat upon. 6200 rpms are always met with shifts and it has no wear . I have 11 vehicles, all running cooler than factory stats. HEAT KILLS. Only reason to run hotter temps is for emissions. I also dyno'd my car on a chassy dyno and the cooler it was, the better numbers were had. Run cool, run hard and live long. As for the graph, I cant believe that you would lose .020 in 50 hours at 140 deg. My bike is air cooled and has 1000s of hours under 130 degs operating temps.. It has almost 100,000 miles.

[Will]

How to avoid sludge buildup: Change your oil regularly and drive the engine hard.

Running it like a performance engine is supposed to be run gets the oil good and heated up, even with a low temp thermostat.

I suppose if all you do is drive your car on city streets during cruize nights and the only time it sees the high side of 4000 RPM is if you rev it up to impress the ricers then you might have a sludge buildup problem.

I have owned lots of cars. Never had sludge buildup problems in any of them. Kept the oil changed regularly, 4000 miles MAX for my 4-cyl. daily drivers. 3000 miles for performance engines that get beat on regularly.

[TransAm525]

Yes, if you're turning 6200 rpm all the time, the oil temps will be high. My old Corvette, with a factory oil temp gauge, would run 180-200 degrees of oil temperature (with synthetic oil) during normal driving, but when I ran it at a constant 4200 rpm during a top speed run the oil temp jumped to 250 degrees. As for the sludge, the oil temps do need to be fairly cold. My 1960 Ford F-100, which uses a 180 degree thermostat, would get some oil sludge in the winter while living in Maryland due to the cold oil temperatures (the engine wouldn't run higher than about 160 degrees unless I blocked off the front of the radiator). The rest of the year I had no problems when the engine was at 180 degrees and the oil temps were higher. I'm not arguing that the effects between 160 and 180 degrees are large, but there is increased wear with the colder temperatures. Some of you running 160 degree thermostats also might be running synthetic oil and turning enough rpm to keep the oil temperatures higher, thus canceling the effects of the colder coolant temperature. If Bronze66 is looking for max economy, I doubt he's turning his engine at high rpm all day, and might not even be running synthetic oil. Yes he could pull a few more hp out of the engine with a 160 degree thermostat, but at the expense of fuel economy and driveability (fuel puddling in the manifold), which seems to be his primary concern. Facts are facts, and running a colder coolant temperature will cause increase wear. Just how much wear depends on the other variables discussed above. Running an engine on a dyno isn't something I would consider as a valid test, as those engines are usually run very hard and at high rpm, which really heats up the cylinder walls and oil. Now if the same engine were ran at 1500-3000 rpm to simulate 200,000 miles of driving, the test would be valid and I think everyone would see what I'm talking about. On an additional note, if auto manufacturers thought the low coolant temperatures were worthwhile, they would install 160 degree thermostats from the factory. If they can figure how to make 400+ hp on the new LS motors while meeting emissions requirements, I think they could drop a 160 thermostat in and tailor the engine to meet the same requirements with the lower coolant temps. The engineers know what they are doing, which is in part of why modern cars run 195-210 degree temperatures.

[lust4speed]

Just using the supplied chart, if the engine performs better between 170 and 185 degrees then it will get the best mileage also in this range. Best performance = best mileage. Only reason for going higher is smog requirements. Back when we still had to pass smog with our older vehicles here, one of the tricks was to block the radiator and get the water temp up over 210 while on the tester because the exhaust was cleaner. Didn't do the engine that much good, but we would pass.

[smagnotti]

Fact! heat is power as far as a reciprocating engine is concerned(think steam engine)
The problem for a internal combustion engine is keeping the air/fuel charge cool as the rest of the engine gets hotter!
I belive Smokey Yunic perfered to run his motors at near 220 degrees, but that left him with little wiggle room on a long hot 500 race.

[Bronze66]

You guys bring up some good points. My thinking on the 170 stat is it will bring the average running temps up in the range of 180-190 depending on outside temps. Which I feel is close to optimal. I normally don't drive this car in 50 degree or below. It gets store in Oct/nov. I'm really interested in fuel mileage. But I did block off the manifold cross over. Always have for power. So that could be a mistake for mpg. I'm keeping records of mileage. I'm going to run it this way for a couple of more weeks and then change the stat to the 170. I'm curious to see if a change in mpg will happen. I don't believe running an engine hot, 195 and above has any benefits for hp or mpg. I want to lean it out some more but don't want to get to the point of being to lean and start to damage the valve seats/faces. The 71 heads have the original seat material and may start to "micro" weld seat material to valve. Hence burnt valve after 40 k miles or so. That was one of the reasons I brought the cr down. I've heard guys say they can get 15-20 mph w/400-455 that had a mild build. That kind of throws a challenge out to see what I can get out of my combo. Plus I like to cruise long trips with this car and wouldn't mind to get mpg like the newer LS1 and the alike. I'm only running a 2bbl if I don't push down over 1/2 throttle. The mention of oil temps. Most measure the temp in the pan. Which I'm assuming is lower than at the bearings and upper cylinder area. I've seen sludge in motors but never in anything I've owned. I don't consider that a problem. Until I get the right speedo gear in the next few days I can only compare numbers with what I've got now. I thought the 2004r would really boost mpg. It doesn't seem that way so far. Then again fine tuning takes time. I like experimenting until I start beating my head against the wall. I end up fixing to many walls that way.

[TransAm525]

Bronze66,

Blocking the heat crossover will be a drawback during the cooler temperatures. I run a Performer manifold with a blocked heat crossover and 180 degree coolant temperature on my 1978 Trans Am (with W72 Pontiac 400). To gain back the atomization lost with the cooler manifold temperatures and my single booster Q-jet, I installed a phenolic 3 hole carb spacer to regain the lost atomization. This is something you can try if you have the hood clearance. On a recent trip I pulled 16 mpg over 1900 miles, but that was with the carb running a little on the rich side and turning 3000 rpm the whole way. I have since tuned the carb and iginition curve and seem to be getting around 17-18 mpg highway.

[Z Code 400]

Originally Posted by TransAm525

On an additional note, if auto manufacturers thought the low coolant temperatures were worthwhile, they would install 160 degree thermostats from the factory. If they can figure how to make 400+ hp on the new LS motors while meeting emissions requirements, I think they could drop a 160 thermostat in and tailor the engine to meet the same requirements with the lower coolant temps. The engineers know what they are doing, which is in part of why modern cars run 195-210 degree temperatures.

Ironic...isn't it??? Most of the aftermarket performance chips for late model vehicles come with 160° thermostats for improved performance and detonation resistance. I think that the number of engines we have torn down over the years with .004" to .006" cylinder wall taper with well over 100,000 miles is evidence enough. Sixt8bird knows this also. If you follow the data on the cylinder wall wear chart you posted, an engine would have over 1/8th inch of cylinder wall wear in around 70,000 miles!!!!

Elevated coolant temperatures are a requirement for clean emissions. Have you ever watched the exhaust gas emissions on a gas analyzer as an engine warms up???

I use steel block off plates on the exhaust crossovers and drill them with a single .090" hole. It provides enough heat for quick warmup and hot air choke function, but doesn't overheat the incoming charge...Robert

[Z Code 400]

Bronze,

We used the leanest settings we could get away with on our street cars...within reason. I would run a 160° Robertshaw Reverse Poppet Thermostat (very high quality all-brass construction) and tailor the jetting for lean-best performance.

4.11:1 gears and a TH200-4R would be a nice combination. I believe that the lower effective ratios would enable you to put the car into motion with less overall throttle opening and the overdrive ratio would yield very good economy...Robert

[TransAm525]

I agree the chart may be a little in the high side, but the effects are still the same. If you ever open up an engine that's been driven by a little old lady to and from the corner store, etc. and has never seen above 2500 rpm, you'll really see the effects of what cold operating temperatures will do. Sometimes the cylinders will ridge so badly you have to pull the pistons out from the bottom, or ream the ridges off, because the rings will catch on the them when trying to pull the pistons out normally. Prior to 1974 there were no emissions standards to speak of, and cars still ran at least a 180 degree thermostat. The only reason the 160 thermostat was ever invented was for use in open-loop cooling systems where 6 pound radiator caps were used, and low boiling points were the limit. All of this aside, it goes right back to what Bronze66 is wanting, mileage, not power. Nowhere is his postings is he looking for more power. His engine would benefit from the higher coolant temperature to help with fuel atomization (especially with a blocked heat crossover) and allow the parts to expand properly to their designed tolerances, thus reducing wear and oil consumption while increasing efficiency. Now if his engine oil temperatures are high enough, then the additional wear is less of an issue, but the driveability problems remain (incomplete fuel atomization/fuel puddling). Nobody is disagreeing the high cooling system temperatures seen today are primarily for emission reasons, but they also reduce wear at the same time. Using a cooler thermostat would be counterintuitive to Bronze66's goal of increasing economy, and would only result in the problems listed above and higher emissions, which is the engine's way of saying it's not operating efficiently as it could be with a higher cooling system temperature. Some of the most experience machine/engine shops will even take this subject to the extreme, performing all their micrometer and feeler gauge measurements in a room with a constantly controlled temperature during the machining process.

I found the website where the graph originally came from--a thermostat distributor. Below is a quote directly from their webpage.

"The all too commonly used 160 degree thermostat is way too low to be considered for performance or engine longevity. As the chart illustrates, engine wear increased by double at 160, than at 185 degrees. So then, why do the 160's exist in the first place? The 160's were commonly used in older, open loop cooling systems where only 6 pound radiator caps were used, and low 212 degree boiling points were experienced. In contrast, modern cooling systems can see upwards of 260 degrees in coolant temperature with radiator pressures exceeding 45 pounds. Many early hot rodders found the 160's to be better performing than the 190's, however, the in between "180" appears to satisfy both ends of the spectrum. The correct water temperature is required for the cylinders to achieve a minimum specific temperature in order to allow a fully homogenized Air/Fuel mixture to combust efficiently. Guess what the minimum number is… right! 180 degrees. Even so, you might see some still recommending the lower 160's, for no other reason than to possibly get that last drop of horsepower out, at the high price of dramatically reducing the life of the engine and it's internal components."