Overheating tripped my Failsafe Thermostat (pics)

Last summer, I put in a new water pump and Failsafe thermostat (got it from advanced auto) along with swapping out the mechanical fan with a FAL 110 fan. All was good and my temps never got above 210, even crawling in traffic on a hot day, both fans cycle on for about 30 secs and the temps drop down to 200.

Last week, it got into the 90's and I noticed my temps slowly creeping above 210 while on the freeway. It stops around 220-230 and stays there even when I got off the freeway onto city streets with stop and go traffic. I thought maybe one of my fans went out, but I pull over and both the FAL and aux fan are on. The temps have come down around here (70-80's now) and now the coolant temps look normal again.

Last night I decide maybe my radiator is clogged or the thermostat is stuck partially open. I decide to use the Prestone 3-6 hour cleaner and Flush N Fill before replacing the thermostat. The back flushed water didn't look too dirty, but my overflow bottle had a layer of gunk on the bottom. Can a plugged coolant overflow bottle cause overheating? As for the Flush N Fill, I think some of you have a firehose to do this because my hose would not push the water out the radiator cap with enough pressure. It would just dribble all over the headlight, so I had to get a piece of large diameter hose from Home Depot to route the flushed water away. I also noticed my Failsafe thermostat was tripped. I guess it did what it's suppose to do. The weird thing I noticed is that they don't tell you what temp trips it into the fail safe mode. What if going from 210-230 is normal?









I replaced it with a OEM one. Does that little hole and check ball even matter with an open cooling system?

That little hole in the OEM one goes in the 12 O'clock position. All OEM thermostats have them and a few aftermarket ones too. Can you 'untrip' the failsafe ?
When you did the back flush did you turn your heater on to max hot ?
Whenever I have done the prestone back flush I put the yellow extension on the rad filler hole and put a 4ft hose on the end of that to drain into a bucket. Also during the process of cleaning my system I remove the overflow bottle and clean it as well as the hose to get all the crap out.

RichP said:

That little hole in the OEM one goes in the 12 O'clock position. All OEM thermostats have them and a few aftermarket ones too. Can you 'untrip' the failsafe ?
When you did the back flush did you turn your heater on to max hot ?
Whenever I have done the prestone back flush I put the yellow extension on the rad filler hole and put a 4ft hose on the end of that to drain into a bucket. Also during the process of cleaning my system I remove the overflow bottle and clean it as well as the hose to get all the crap out.

Click to expand...

I've only ever gotten Stant and Failsafe thermostats and neither of them have the little hole. I think I could untrip the fail safe tangs, but you'll see that it's a 180F thermostat and I've decided to go back to a stock temp one. My mileage and performance has been pretty much the same while running 180F thermostats for the past 3 years, with just slightly lower temps during momentary idling and freeway driving.

Yeah, I had my heater at full blast. I guess someone here posted a pic of water shooting out the yellow extension, like 4 feet away. I expected that to happen, but it didn't. I think I did the a good job cleaning. I emptied the radiator, poured in the 3-6 hour Prestone cleaner with distilled water, drove for 4 hours, emptied it back out, back flushed with Flush N Fill with heater open, emptied it out, poured in straight distilled, idled at operating temp for 10 mins with heater open, emptied again, then put in 50/50 with some Redline Water Wetter.

I noticed that I only put in about 8 qts (2 gallons) whenever I open the drain on the radiator. The FSM says the cooling system takes 12 qts (3 gallons). I'm guessing I have 1 gallon of distilled left in the block after my last drain, so should I put in 1 gallon of straight coolant then get it to full with a 50/50 mix?

What I usually do is once the enigne is ready to be refilled [I drain it from the lower hose, not the rad drain, thats a PIA] is dump in a gallon of pure antifreeze, then start the engine. I take a gallon of distilled water and dump half of it in the empty antifreeze container, then dump half of another pure antifreeze container in the half filled with distilled water one, that one is now at 50/50 then dump the remaining distilled into the half empty one and end up with two 50/50 mix containers, from there it's just a matter of topping off the system. I keep the filler neck on the rad full and you can see the green soda like bubbles as the air bleeds out, I also fill the overflow up to the hot mark. On the last two 'top offs' I bleep the throttle so the coolant gets sucked down, top it off real quick and slam the pressure cap on. From there it will bleed itself over the next few days...

just stoped by to buy some time. sorry i can't help out, but one question.


how can you take so many pics of one thing???????

Have you considered using a high flow t-stat such as from Hesco?

It looks like your fail-safe was a180 degree t-stat. It is not a good idea to use one less than say 190. Remember a lower temp. t-stat will not make your engine run any cooler, the t-stat just opens earlier. These engines are designed to run between about 190 and 215 degrees. When the t-stat opens too early it will cause the engine to run too rich.

It's 2006, bandwidth and memory are cheap.

Yeah, I wanted to use the Hesco/Mr Gasket high flow one, but no one really keeps them in stock and I had to get it fixed ASAP since it's a DD.

Yeah, I mentioned it's 180F and now I'm switching back to a stock one. I never got any signs of the engine running rich for extended periods of time in the 3 years running the 180F, not even in the winter.