Temperature fluctuates quickly (1 Viewer)

[nodaksn3]

Question (1):
My '99 with 255,xxx well- maintained miles has begun to have pretty quick temp variations on my scan gauge while driving the hills of West-by-God Virginia. It remained fairly steady at around 202 all the way across country until we hit WV. Now, yesterday, while hill climbing on I-79 north, it reached 206-207, then down the other side dropped quickly to 197-198 or even lower.
Question (2):
When I checked under the hood, I noticed the electric fan not functioning, so I had the a/c recharged this morning (it always has blown cold) so now it's even colder. It was slightly down .2 or so pounds. But the fan still shuts off. Shouldn't it run all the time when the a/c is on? Not sure if the temp thing is related, but I'm thinking that might be the thermostat, which was replaced at 180,000 along with the timing belt and water pump. Might it be sticking closed? Or open? Coolant level (red) is OK, no leaks or other issues.
Any ideas on these two things?
Thanks for any help, Ned

 

[outdoorsman]

Electric fan is only there to help the A/C perform better. The stopped installing them in 2003 up.

Maybe clogged radiator, low antifreeze or worn out fan clutch

Did you use OEM parts when changing water pump,...., t-stat?

If radiator is original it is time to replace it.

If you replace the fan clutch use AISIN FCT-021

https://www.amazon.com/gp/aw/d/B00829HCD4

 

[flintknapper]

Your engine coolant temps might be normal for the conditions you were under. Not knowing how steep or long the hills you traveled were. But if you suspect sub-par cooling...you might check (or have checked) your fan clutch.

As for the electric fan (A/C condenser fan)..NO it will not run all the time. IIRC it is set up to switch on at a predetermined line pressure (about 220 psi I believe). It would be activated by a trinary switch located somewhere on the high side line of your A/C system. I'm sure there is a relay involved as well.

But once the line pressure drops below a certain point, it would shut off. (Or never run at all if pressure didn't exceed the specified minimum). If memory serves...the electric fan was found on 98-02 models and dropped in 03.

Some folks with 03 and newer cruisers add one as an 'Aux fan'.

Edit: ^^^^^^ hah @outdoorsman types faster than I do.

 

[nodaksn3]

Thanks guys. The radiator was replaced a few years ago with a Koyo. Fan clutch no. OAT is around 85, but it's humid unlike Phoenix. I still suspect the thermostat might be stuck, but we'll see after we arrive in Mass. I'll open it up.

 

[05JLX470]

That doesn't seem like a very big fluctuation in temp to me under those conditions. Temp came up some under load and down some under no load. Can't comment on the electric fan as I have an 05. If your thermostat was stuck open or closed you would see either high temps or low temps all the time, not both. Keep us posted what you find............

 

[abuck99]

Those running temps are a little high compared to a healthy cooling system. With a new radiator, fresh coolant, in proper working order your temps should fluxuate between 186-190.

Radiator & coolant: when was the last time coolant was flushed? Is the radiator original? Check that when the thermostat was installed that the jiggle valve positioned up.

I suspect your radiator is not cooling very efficiently- clogged rows, or build up on the outside of the radiator impeding air flow.

I recently swapped my radiator (186k) and found some of the cause of the higher temps: debris clogging the lower section of the front side. And noticed the inlet was very discolored and brittle. Its life span was nearing the end.

 

[05JLX470]

Those running temps are a little high compared to a healthy cooling system. With a new radiator, fresh coolant, in proper working order your temps should fluxuate between 186-190.

Radiator & coolant: when was the last time coolant was flushed? Is the radiator original? Check that when the thermostat was installed that the jiggle valve positioned up.

I suspect your radiator is not cooling very efficiently- clogged rows, or build up on the outside of the radiator impeding air flow.

I recently swapped my radiator (186k) and found some of the cause of the higher temps: debris clogging the lower section of the front side. And noticed the inlet was very discolored and brittle. Its life span was nearing the end.

View attachment 1707057 View attachment 1707058 View attachment 1707059

Looks like he replaced the radiator a few years ago with a Koyo.

 

[SHIfTHEAD]

I think you are overly sensitive to the numbers. First, lets not forget that water, at sea level, boils at 212 degree F. That number is increased in two ways in a cooling system. First the systems don't run pure water; Anti-freeze is also Anti-Boil. Second the system is pressurized, which has the effect of raising the temperature at which water can turn into a gas. Also, the system cannot maintain an exact temperature since the thermostat is a bimetallic device that uses temperature changes to open and close, which does not happen instantly.

So, I would say to chill, temperature fluctuations are expected. If it were me, I wouldn't worry unless I saw the temps get up around 220 or more.

 

[05JLX470]

Not sure what the ideal temp is on our 4.7's, but these are in the category of modern day engines, and most all modern day engines are designed to run hot due to emissions. I was born in 1965 and I remember in auto shop we would change thermostats out and they were 170-180. Not the same thing today. Newer cars run 190-220 range.

 

[flintknapper]

Thanks guys. The radiator was replaced a few years ago with a Koyo. Fan clutch no. OAT is around 85, but it's humid unlike Phoenix. I still suspect the thermostat might be stuck, but we'll see after we arrive in Mass. I'll open it up.

^^^^^ Thankfully not hard to do. Remove air intake box, remove upper radiator hose at thermostat housing. Remove the three bolts holding the housing (you'll lose a couple of quarts of coolant, if radiator is not first pre-drained some). Install new OEM T-stat and gasket (jiggle valve at 12 O'clock). Button it all back up. Add coolant, leave radiator cap off. Start engine and let idle for 10-15 minutes (or until it reaches operating temp.) Install radiator cap. Check overflow tank level after your first drive (heat and cool down cycle).

I just replaced my T-stat recently (Toyota). It had failed in the closed position and the radiator boiled over just as my wife (who never looks at the gauges) was pulling into work. Since then....I have installed a Scangauge and instructed her to look at it from time to time. But in all fairness....the factory temp gauge has a HUGE dead spot in it and by the time it starts moving from the middle position...you are well on your way to over-heating.

T-Stat # 90916-03100
Gasket # 16346-50010

 

[abuck99]

I think you are overly sensitive to the numbers. First, lets not forget that water, at sea level, boils at 212 degree F. That number is increased in two ways in a cooling system. First the systems don't run pure water; Anti-freeze is also Anti-Boil. Second the system is pressurized, which has the effect of raising the temperature at which water can turn into a gas. Also, the system cannot maintain an exact temperature since the thermostat is a bimetallic device that uses temperature changes to open and close, which does not happen instantly.

So, I would say to chill, temperature fluctuations are expected. If it were me, I wouldn't worry unless I saw the temps get up around 220 or more.

IMO- be sensitive to cooling temps in your 100. 2UZFE Aluminum heads mounted on iron block that have a known tendency to warp ( in the center); you dont want to ignore higher than average running temps that may eventually contribute to a HG leak.

Fluctuating temps are normal by 3 to 4 degrees as the t-stat heat and cooling system pressure cycles, but constant operating temps over 200F+ in a 100 series is worth paying attention to. Being aware (sensitive) to the numbers can save you from an impending failure and damage to other more expensive components. The 2UZFE in 100 series typically runs in mid-high 180's low 190's depending on the season, type of use, age and health of the cooling system and fluids. Monitoring a scanguage or Torque app will help establish baseline and awareness of specific operating temp range under various conditions and seasonal changes. If you start to see your average running temps creeping upward over time, and spiking over 200 consistently you'll want to start paying attention to why that is happening.

We generally know what the optimal running temp range is in a fresh 100 series cooling system is 186-190f ( flushed system, new radiator, new coolant, new water pump, new thermostat, good fan clutch). Regardless of the thermodynamic theory of of fluids under pressure, and the boiling point of properly mixed coolant, or what the temp range is of other cars: what is most relevant to 100 series are consistent coolant temps in the low 200's being an early warning sign to pay attention to (in a 2UZFE equipped 100 series).

 

[flintknapper]

^^^^^^ Sage Advice.

 

[nodaksn3]

Thanks all for the info! When we get to Mass. I'm going to have a serious look at it. Since it's been running at 202 after I replaced the timing belt and radiator, I'm thinking the thermostat is too high and I'll replace that and flush the radiator, replace hoses, etc. In another 20,000 or so I will replace the timing belt, water pump, and so forth.
Thanks again, Ned
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[nodaksn3]

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