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Discussion Starter · #1 ·
So you dont have to go through all the threads....

Had a fluctuating temp issue for a while...rev the engine and it could drop back to normal after floating up a bit...never overheated.

Swapped the temp sender, drained the coolant and put fresh coolant in and the issue went away...or I thought.

After a week or so it came back...the fluctuating temp on the gauge. Not much of a float...but it went up and down a few times, especially at intersections.

Pulled the thermostat and did a better flush (in my mind)....new thermostat and the issues went away for a week or so.

Did a road trip and about 400 miles in the temp started fluctuating again...going more to the hot, then back to normal. Stopped and checked things...no boiling over or signs of boiling over while driving.

100 miles later it pegged hot and started to smell coolant...pulled over and the upper multi hose coolant hose had split at the plastic. Towed it home.

Once home I have...

Replaced the hose, drained and refilled the coolant. Drove it 1/4 mile and pegged hot again after idling for 20 min at normal temps.

Was reminded I had no heat last winter....check the heater core and got no flow...

Replaced the heater core...it was plugged with rusty sludge. That was a bear of a job.

All back together....after running for 45 min idling and reving and refilling the coolant...the gauge moved to hot...and pegged driving it in the yard.

Replaced the temp sensor with a new one.....still pegs hot when driving...

Below are the temps I am getting with an infrared thermometer:

5 min idle:
Top Heater Hose: 103
Bottom Heater Hose: 108
Thermostat hose: 119
Upper hose (right side of radiator) 112
Lower Hose (Left Side of radiator) 98

At Top Dead Center Temp Gauge (fan on)
Top Heater Hose: 106
Bottom Heater Hose: 115
Thermostat hose: 132
Upper hose (right side of radiator) 162
Lower Hose (Left Side of radiator) 173

3/4-Pegged Hot Idling:
Top Heater Hose: 160
Bottom Heater Hose: 146
Thermostat hose: 162
Upper hose (right side of radiator) 150
Lower Hose (Left Side of radiator) 160

15 minutes of running at 3/4/pegged Idling
Top Heater Hose: 148
Bottom Heater Hose: 143
Thermostat hose: 173
Upper hose (right side of radiator) 132
Lower Hose (Left Side of radiator) 158

My lower hose is getting hotter than the in inlet....so does that mean it is the radiator that is an issue? Plugged?
The fan is running as it should...changing speeds and running after I shut the car off...lowering the temp afterwards.

Could it be the water pump?

Need some help...

Thanks!
 

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It is concerning that your heater core was clogged with rusty sludge. Makes me wonder what else may be clogged. Have you replaced the radiator?
 

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2007 Volvo V50 T5 AWD M66
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I know these doesn't go often but water pump.
 

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Discussion Starter · #4 ·
That was my next step....but...

none of my measured temps are near overheating numbers, yet the gauge is pegging (this is the 2nd new temp sender in this process).
 

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Discussion Starter · #5 ·

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Discussion Starter · #6 ·
Alright....car is running great. Temp gauge is perfect, temps are good....been on a few test drives and all seems well.

What did I do this morning? Nothing. Started it up to do a couple temp readings and everything is back to normal.

It is a blessing....I was about to drive it to the burn pile!!!

Thanks for all the suggestions. Gonna keep a close eye on it and see how it goes.
 

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You may have had a bubble in the system that worked it way out.
 

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These systems are best filled using a vacuum bleeder To avoid trapping air in the system.
 

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2007 Volvo V50 T5 AWD M66
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Water pump because of the temperature fluctuations when you rev. Seams like it's struggling to pump liquid around the system. If you found lots of rust in your heater core not much is iron besides the water pump fins.
 

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Hence water pump not air pump. Once the problem is sorted, ie water pump swap etc.
Use the vacuum pump to make sure there isn’t any large pocket of air in the system.


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Was reminded I had no heat last winter....check the heater core and got no flow...

Replaced the heater core...it was plugged with rusty sludge.
BTW, there's no way that "rusty sludge" should be in the system. There's almost no iron in it! The block, radiator and heater core are all aluminum.

It sounds to me like someone put phosphate-type antifreeze in the car. This reacts with the aluminum and can cause powder to form which will clog passages. Perhaps it picked up some other contaminant, and it looked rusty. I'd consider a chemical flush, maybe two, and a refill with the proper coolant formula.
 

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Discussion Starter · #12 ·
Did several flushes, including a chemical flush...everything is checking out fine now. May have been air in the system...who knows...

I drove it to a mechanic friend....he double checked everything and all is good.
 
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