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The upper rad hose clamp broke and the upper hose came off while driving last week. I put on a new clamp and refilled the system. On our 1st hot day this year here in Chi-Town, coolant suddenly started overflowing from the reservoir cap.

Bad cap or perhaps bad thermostat? How do I diagnose the thermostat?
 

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...
How do I diagnose the thermostat?

Just.

Don't.

It's a farkin' TS.
It's a farkin' maint./ item.

Get a farkin' new one. jk or lol or haha


Seriously, heard 4 decades ago if'n ya overheat real bad once then your TS might end up toast. Long story about my wife's Explorer -- yah so won't dare bother with details, but end story that's what I confirmed 17 years ago using it to take a stove to a colleague.
 

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The upper rad hose clamp broke and the upper hose came off while driving last week. I put on a new clamp and refilled the system. On our 1st hot day this year here in Chi-Town, coolant suddenly started overflowing from the reservoir cap.

Bad cap or perhaps bad thermostat? How do I diagnose the thermostat?
It's worth asking....are you sure you properly bled the air out of the system? Trapped air can cause the engine to overheat and push out the coolant.

As for the farkin Tstat 0:) you can take it out and drop it in a pot of hot water (Tstat temp) to see if it opens. But for me, at about $10-$15, just replace it and the oring gasket.
 

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Or,the 160 degree version for just a couple bucks more. If you don't recall when cap was replaced,get one of those too.
 

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Discussion Starter #6
Funny, I picked up a new TS from O’Reilly’s and dropped it in. Normally on my temp gauge, the needle is on the fourth line which is the very center of the gauge . Since this new TS, the needle only goes up to the second line.

What are the advantages and disadvantages of running 160° TS? Will I get less heat in the winter with the cooler one?
 

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Thermostat is super easy to swap if you feel you need more heat in the wintertime. Personally,I find heat to be satisfactory...
 

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Thermostat is super easy to swap if you feel you need more heat in the wintertime. Personally,I find heat to be satisfactory...

From what I hear be sure to combine a 160 TS change with appropriate programming or that TS and the fan kick-ons will fight each other.
 

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Fans will operate as before,but will operate less... If install a hotter stat with reprogrammed fans is where issues with fan operation occurs.
 

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Depending on your cooling system the only real problem is you may never get into full "run" mode where your reading the O2 sensors and it dumps more fuel into the system. Which requires a reprogramming to knock it out of Open loop. (Open/Closed loop are where the O2 sensors are ignored or looked at for fuel management. The idea is to get your engine up to temp faster so the pollution controls work quicker. But I never remember if Open or Closed loop is the phase where it ignores the O2 sensors and dumps fuel. Thought Closed loop is normal operation and Open loop is startup but I could be wrong.)
 

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Closed Loop is when the oxygen sensors are used or "complete the cycle" of combustion.

Nab
 

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Closed Loop is when the oxygen sensors are used or "complete the cycle" of combustion.

Nab
Thanks...

When I put the 160 degree stat in my car the fuel mileage went down because it never got out of open loop. Adjusting where closed loop starts makes a big difference. Been so long though that I don't have a clue where mine is set. I probably should try reading the program but it has been over a decade since I touched it.
 

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I had a running hot issue a few years back .. noticed that the hoses were very hard with ac on 90f air temps.. so I found that the pressure cap did not vent out the pressure @15psi so it messed up the flow of coolant.it does happen the cap vent can get plugged up.. so I did have to replace the upper radiator hose as it got damaged from the hot temp and higher pressures..using a screw on clamp IMO not good ....


when the coolant is drained then it may take 3X to bleed the system.. I just replaced radiator as the plastic side tank cracked ... as expected it did take a few bleed cycles to return the temp gauge to normal which is 1/4 mark...if it goes to the 1/2 area ,,,air will do it or a head gasket if it continues to have air ..
 

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When I put the 160°F stat in my car the fuel mileage went down because it never got out of open loop. Adjusting where closed loop starts makes a big difference. Been so long though that I don't have a clue where mine is set. I probably should try reading the program but it has been over a decade since I touched it.
Many years ago (1998), I installed a 160°F/71°C tstat on my very 1st Caprice 9C1-LT1.
Whenever the ambient temp got below freezing, it would bounce in & out of open & closed loop so long as I was cruising steadily over 50MpH or so.

Blocking off the external motor oil cooler, removing the radiator's airdamn, & covering up the bottom-most 4th of the radiator [with the airdamn] was enough to keep it in closed loop permanently.

Reinstalling the 180°F/82°C tstat, however, improved both the MpGs, and the heat of the hot air blowing out of the HVAC, so I started using 180°F tstats for the winter, and 160°/71°C tstats for the other 9 months.
Until I started reprogramming pcms for myself, that meant using fan-on temp thresholds of about 201°F/94°C & 210°F/99°C all year round.

Anyway, even when it stayed in closed loop with the 180°F/82°C tstat, my winter MpGs never really approached spring/fall MpGs, til I got decent at personalising my tune - which took the better part of 2 years.
 

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On a whim, I just did some checking around on the interwebs.

1. I don't think MotoRad bothers to make FailSafe 7307-160 thermostats anymore.
2. To get MotoRad 307-160 thermostats [once RockAuto runs out of them], you're probably gonna have to get them from HyperTech.

I hope I'm wrong.
 
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