Lower thermostats, really needed?

[digitalfiend]

I've got a 2004 Tahoe that I'm going to be converting to electric fans. I hear you loud and clear when it comes to keeping the stock thermostat. I hope this isn't too far off-topic for you, but can you make any suggestions on what temperature to tune the engine's computer to turn on the electric fan for low and high speeds?

 

[TahoeLimited]

I believe a motor that's running cooler will be less likely to detonate. Of course, if it's knocking, putting in a cooler t-stat isn't fixing the real problem...just sayin'.

 

[JennaBear]

I've got a 2004 Tahoe that I'm going to be converting to electric fans. I hear you loud and clear when it comes to keeping the stock thermostat. I hope this isn't too far off-topic for you, but can you make any suggestions on what temperature to tune the engine's computer to turn on the electric fan for low and high speeds?

Depends on the parameters of the vehicle.

Sent from a jelly bean.

---------- Post added at 01:33 AM ---------- Previous post was at 01:30 AM ----------

I believe a motor that's running cooler will be less likely to detonate. Of course, if it's knocking, putting in a cooler t-stat isn't fixing the real problem...just sayin'.

That is actually a common misconception. Detonation is generally unrelated to coolant temperature. Intake temperature is a different story.

Sent from a jelly bean.

 

[ccapehartusarmyINF.(ret)]

running your engine cooler was the big thing way back in the 70s but weve learned that your engine has to run at a certain temp running at lower temps puts more wear and tear on your motor your motor should run in the 200 range its fine as long as it doesnt go over the 210 220 range coolant biols at 212 dag. but since your colling system is under pressure your bioling temp is 245 dagrees running your engine under 180 is very bad and if you think its good have fun in 50 k miles

 

[Hacker-Pschorr]

That is actually a common misconception. Detonation is generally unrelated to coolant temperature. Intake temperature is a different story.

Not really.

You are correct in your initial post that a lower thermostat doesn't lower intake air temps. I've honestly never heard anyone claim that was the reason to run a lower thermostat.
You run a lower thermostat to lower the overall operating temperature of the engine which does lower the detonation threshold. This is well documented, no myth or theory - but not the best idea for a daily driver.

Engine temperature is a balance. The hotter you can run an engine the more efficient it will be (to a point...). A hot engine is great for gas mileage but also increases the detonation threshold.

The cooler you can keep the combustion chamber, the lower the detonation threshold is going to be. The best way to keep the combustion chamber cool is to lower the operating temperature of the heads (oil squirters also help by lowering pistons temps).

The problem with this (as you already mentioned) is an engine that never reaches 212F will not boil off the condensation that has accumulated in the oil. If you've ever seen a "peanut butter" build up in the oil filler or on the dip stick - this is a sign of condensation issues (could be other things too, just an example)
This is why short trips are so bad for an engine, just because you coolant gauge shows the engine is warm, that doesn't mean the oil is up to temp.
I've owned cars with a temp gauge for both, and most would be surprised how much longer it takes for the oil to reach full temp, especially in winter. This is why most production cars have oil coolers in the radiator. This approach has more to do with getting the oil up to temp quicker than a better cooling.

Also, just dropping in a colder thermostat doesn't tell the computer anything other than the engine is running colder, which it's not properly mapped for. In order to see any real gains with a colder thermostat you need to re-tune the engine for the colder operating temps. With some vehicles (older speed density Fords come to mind) if you keep the engine below 180F or so, the engine will stay on the warm up map and run super rich all the time.

On cars with stand alone ECU's, you can setup a warm up map that brings the oil temp up to 212F + to boil off any moisture then keeps the engine at a specified lower temperature with completely different ignition and fuel maps for each range and everything in between.

Bottom line is, the colder you can keep the combustion chamber the more aggressive you can get with the ignition timing to increase power. In boosted cars (like the Grand National mentioned above) this is huge.
Yes lower intake air temps are important but the temperature of the combustion chamber is just as important if not more so.

 

[TahoeLimited]

Not really... QUOTE]

Thank you. I was fairly certain I wasn't insane if knowing that my cars had significantly more power when probably about 160...especially my Grand National... I now have a '98 Regal GS and it's one of the first things recommended to reduce KR, which is very commonly monitored. I haven't done my own KR comparison, but it's just not debated there. It's stated as fact that a 180 degree t-stat will lower KR vs. the stock 195.

I had a '68 Chevelle SS years back. The radiator hose split while I was on the freeway. I started hearing it knock, realized it was overheating bad and by the time I pulled off the freeway, it was so hot it was knocking like you wouldn't believe even at idle! And it was "dieseling" so bad...it simply stayed running after the key was off...like for a minute. I had time to open the hood, unscrew the air filter lid, and stuff a shop rag down the carb to suffocate it! Point being...the overall engine temp was so high, it was knocking at idle. So especially with a car with a knock detector, which will pulling timing when knock is detected, indirectly at least running cooler helps. The other very popular first mod for the Regal GS's is the cooler burning Autolite 104 spark plugs.

 

[JennaBear]

If that was true, you would see NASCAR running colder engines. They run at 230-240 degrees.

When we've had vehicles on the dyno, which we've had many they are capable of making more power at a higher temperature than colder. As long as air temperature is constant, power goes up as temperature goes up.

The belief that more timing = more power is false as well. Power increases as timing increases until MBT is reached. From that point on, timing can be increased to an extent and no additional power is made or power even starts to drop slightly until knock occurs. In many cases, MBT will be 3-4 degrees before knock occurs.

Comparing these engines to an older carbureted engine doesn't work in this case. Metal intake manifolds conduct all of that engine heat to the incoming intake air charge as well as fuel sitting within the carburetor.

 

[Hacker-Pschorr]

If that was true, you would see NASCAR running colder engines. They run at 230-240 degrees.

The absurdity of bringing up NASCAR in this discussion about street driven SUV's is beyond my comprehension.

230-240 degrees? I know road racers that would love to be able to keep their engines that cool during a 45 minute sprint race. Doing so during a 500 mile endurance event is a phenomenal task.

Also, any reduction in cooling would mean more air flow which means more drag......remember above where I keep saying everything is a balance? Yup, applies here..... Not to mention the body work is heavily regulated anyway, so it's not like they can really change anything.
Even adding a thicker radiator would be enough drag to lower the top speed in a cup car.

You do realize the boiling point of a NASCAR engine is upwards of 300 degrees due to the extreme pressures they run (compared to a street car). If you were right, they would be pushing those limits to run the engine as hot as possible....news flash, they don't.

Bottom line (again) and the only reason why I entered this thread is I've never heard anyone associate a lower thermostat with cooler intake air temps. You are 100% correct with your advice here..... however.....
The reason why anyone would install a colder thermostat is to lower coolant temperatures, more importantly in the heads.

It's this simple: When you lower the combustion chamber temperatures you lower the detonation threshold.

Did I ever say lowering the detonation threshold automatically or guarantees a power increase? No, I did not......

 

[JennaBear]

So then we agree, thermostats are not cooling devices. They will not cool your engine down.

Sent from my fone.

 

[turbopowered68]

Not Convinced...

I've owned several Buick Grand Nationals (5, actually), and one of the most popular initial mods is the 160 deg. t-stat. Maybe it depends on the engine, but I'm very confident that my GN had an easy 40 more hp when it just warmed up enough to give it some throttle. I always looked forward to that first blast when coolant temp was about 140 deg...it was a rocket. Fast forward 20 minutes later, and definitely a noticeable loss of hp. Okay, so some of it may be the intercooler heating up. But even after long periods of cruising, to allow the IC to cool down, it was never as fast as the first blast ~5 minutes after heading out.

I *just* bought an 00 Tahoe Limited 3 days ago, and think I can also detect a hair of the same phenomenon...seemed extra peppy at about 160 deg. on the temp gauge on it's way up to fully warmed up.

Aside from Buick Grand Nationals, which my confidence is high, one can argue back and forth all day. The real test isn't easy - several dyno runs with the same outside temp with higher and lower degree t-stats.

On a related note...I may need a new t-stat. I've noticed the temps hitting over 200 (close to 210 maybe) before the t-stat opens...don't like it.

I also own two GN's an 86 and an 87 --- you comparing technology that is 30 years different, head, combustion chamber, and COOLING design. the GN's cooling system cools the block first then heads, these truck motors cool the heads first then the block. the GN has a Turbo which generates a ton of heat once it starts producing boost, these motors don't have that heat generator. Regardless of compression of these truck motors will NEVER see the same cylinder pressure the GN does that is also another reason the GN needs the cooler system.
BTW put some picture of the GNs i would love to see them.