Coolant Temperature Changes & RPM's

[abuck99]

My operating temps have been consistently running around 198' this summer in 90'+ plus ambient temps. My driving habits are pretty easy on the throttle, and I generally dont operate much above 2200-2300rpms.

I was doing a fuel system cleaning and running around in 2nd & 3rd gear on local streets in 4th( I have a 5spd) on the hwy keeping the RPM's upward of 3,000-3200. I noticed my operating temperature actually drop down to 193' the more I pushed the engine rpm's up.

It's counter intuitive (to me) that running the motor harder, is cooling the engine better. So I am wondering if the difference between higher operating temps at low rpms and lower operating temps at increased rpm's is indicating a internal flow restriction, or external air flow restriction somewhere. Or is this normal?

What is the probability of the temp variance from:

• Blockage or flow restriction in the radiator?
• Failing water pump ?
• Failing Thermostat ?
• Clutch fan ?

Coolant was flushed and replaced with Toyota SLL 6k ago
Heater T's were replaced 60days ago
TB/WP/Tstat done 2010/ 77,000 miles ago.

 

[montegofd3s]

Man, your temp will fluctuate 5 degrees all the time. Don't worry about it. Mine bounces between 185-205 depending on driving conditions. It is perfectly fine. It probably just dropped when you were watching due to the increased coolant flow/airlfow/intaketemp when you increased rpms.

 

[Trunk Monkey]

Normal. Lugging the motor in a higher gear, lower speeds, and lower RPMs doesn't circulate air and coolant efficiently. Same reason you kick out of O/D when towing up a grade, slightly higher RPMs keeps the tranny and engine cooler.

 

[DTCsk8er]

As the previous guy mentioned.. this is normal. The thermostat opens/closes as temps rise/fall, allowing for coolant to move/stop throughout the engine/radiator/etc. It is normal to see temps fluctuate a little bit as the thermostat cycles.

Not a sign of failure of any of those items IMO

 

[ton504]

Must be the headgasket. Seems like its time to pull out the engine and rebuild it. Lol sorry I hang out in the 80s section too.

Like others said, you probably don't have a problem.

 

[Spike555]

From a guy who used to be cooling system certified...it is the LOAD on the engine not the RPM that increases engine temps.
The faster the water pump moves coolant the cooler the engine will run (to a point obviously)
The best and fastest way to cool a overheating engine is to put it in neutral and increase engine rpm, this is assuming there in no coolant loss.
The electric fan in your front wheel drive car doesn't work and you're stuck in traffic with no where to go? Increase rpm to around 1800 and turn on the heater.
Engine load, coolant flow, air flow and heat transfer rate are what keeps an engine cool.

And the reason for downshifting when towing up a long grade is to keep the engine in the power band as well as keep the water pump moving faster.

It is a common misconception that the longer the coolant stays in the radiator the more it will be cooled, this is false.

 

[abuck99]

Must be the headgasket. Seems like its time to pull out the engine and rebuild it. Lol sorry I hang out in the 80s section too.

Like others said, you probably don't have a problem.

Ok @ton504 funny- (smart-arse) Seriously thanks for the all the replies- the helpful and the humorous.

I monitor the temp pretty closely since installing the Scanguage. I had not seen it drop to 193 since winter weather, and was surprised to see the temps drop as I applied consistently higher rpm's outside my normal operating range. Good to know my cooling system works more efficiently when engine is working harder.

 

[ton504]

Higher rpms doesn't mean its working harder...If I'm climbing a steep bridge in my 80 and I don't give it enough throttle to downshift, I can see the temps rise. But when I do give it more throttle, it downs shift/raises engine rpm and cools down since theres less load. I mention my 80 since I don't have a digital gauge in my 100.