random overheating solved but need thoughts

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random overheating solved but need thoughts

September 21, 2014, 08:30:50 PM

been chasing what I assumed was a valid over heating issue with my 20th 5.0. Some of the hardest problems to find are those that deal with something partially broke or intermittent.

over the past few months out of the blue my temp would get high,, and oddly enough most prevalent during the night.

last thurs night on my way back from Birmingham AL, it got oddly higher then the problem went away.

I had totally forgot to do a simple check so yesterday after I did the TFI relocation, I test drove the car and it got max hot to the point the overflow spilled over.

In the recent month I did change the tstat and I found the old unit was stuck open,,, replaced and things seemed a little better till yesterday when it all started up again getting hot.

I pulled into the drive it dawned on me to reach inside the fan shroud to feel the radiator. The lower half was bone cold , the upper half was way way hot.

I swapped out the radiator today ,,, and finally to the reason for this post...............

I add coolant then start the car without a cap on, I notice the water flowing through the radiator tunnels spilling over like a water fall. This to me is only possible If the Tstat is stuck open because my engine was bone cold during this repair.

What are the odds my new stat is stuck open? By design to they "thermal" themselves open when they get *too hot* ?

I know some things in the mechanical world thermally protect other connected parts but I wondered if in the making of a Tstat do they do a solder link of sorts that upon a certain temp the thing will stick or "thermal" open?

I think I can check this by blowing directly into the upper hose and if I kick coolant out the fill cap that means it stuck open,,, which isn't good on a cold motor.

random overheating solved but need thoughts

Reply #1 – September 21, 2014, 08:42:05 PM

As a fyi the coolant is always circulating when the engine is running. The bypass hose allows coolant to bypass the closed thermostat. Whenever I start a car I just refilled the radiator on (and filled the radiator to full) with the cap off within a minute or so coolant will spill over, even before the thermostat opens. Once the thermostat opens the level drops and the coolant stops spilling over. Then you just top the coolant off and put the cap on.

random overheating solved but need thoughts

Reply #2 – September 21, 2014, 08:58:17 PM

speaking to the bypass,
I thought the flow went around the stat meaning water pump pulls from the block , pushes up to the heater core then back down into the block.

are you sure ?

Ive never had water running immediately through the radiator fill cap area on a cold motor. If it were that means its coming from the open door way (tstat)

random overheating solved but need thoughts

Reply #3 – September 21, 2014, 10:24:29 PM

With the coolant overflowing I'm referring to just having refilled a cold radiator to the bottom of the fill neck. Once started with the cap off coolant should start slowly spilling out of the neck after about a minute of run time. Once the thermostat opens the level will drop and you should see fluid moving through the tubes (which will now be exposed because the coolant level has dropped).

Most thermostats have a small (1/8" or less) air bleed hole. Coolant can move through this hole even with the thermostat closed. The bypass does bypass the thermostat so coolant is constantly moving when the engine is running. It's just not going through the radiator.

It's possible that if your engine gets very hot the thermostat can fail open. However with an open thermostat (after the overheating problem has been corrected) the engine will run very cold.

random overheating solved but need thoughts

Reply #4 – September 22, 2014, 09:49:30 PM

well,, this aint cutting it... my full electronic cluster never went over 2 bars today,, which according to my radiator cap with a built in tstat shows 120degF.

Time to make it get more heat,, how ironic

so im guessing the tstat is stuck open

random overheating solved but need thoughts

Reply #5 – September 22, 2014, 10:24:07 PM

It seems trivial....I wish I could get an industry-inside scoop, but I've bought nothing but the expensive (usually Stant "Superstat") tstats ever since the first overheating problem I had in a vehicle drove me bananas. Absolutely have to isolate out that component and know that it's directing flow as needed. Depending maybe ENTIRELY on the system design...a wide-open stat could make it run too cool, or too hot depending on what heat transfer actually takes place in the radiator. I fell for that trap thinking I'd get away with something.

As Lou said...you *think* you're seeing flow through the radiator. It's a trick of the mind--what's happening is that's just the water slowly "falling" out of the tubes. They don't flow that fast, and don't need to in order to accomplish their intended purpose.

I can't back it up with data but I've many times heard old timers say once you overheat a car, don't expect the stat to be okay. I'm sure it's not *good* for it, there's a safe assumption anyway.

The bypass lets coolant flow to your heatercore, and then back into the lower intake manifold jackets.
If your stat is stuck closed, remember the lower radiator hose remains a free path. Pressure builds, possibly violently/quickly enough to surprise you/catch you off guard (get a THICK rag and THICK gloves when you think you're gonna just pop that cap off even though they told you not to!

) and heat travels in strange ways.

Radiators are like filters and I can't help but feel like *many* cooling problems are a plugged radiator. Here's a good test - PITA since you need to drain and contain your antifreeze - or rig up something to contain this experiment. But get your car hot, and get a bucket for the upper hose to just dump into. Maintain the water level in your radiator, point that hose into the bucket, and rev the engine. You might be blown away by how much water that pump moves. It'll drain your radiator before you can think "ooo I'd better check the level" Good way to confirm your pump works. :) Then....assuming the block water jackets aren't plugged solid....you've basically got the tstat...and the radiator.

Now....if the air coming off the radiator is always hotter than hell....might be a bad fan clutch. Kinda same story. A good fan clutch moves HELLA air. I don't know how the hood blankets don't get ripped off...

random overheating solved but need thoughts

Reply #6 – September 24, 2014, 12:44:01 AM

looks to be the problem,, this one is about 3 weeks or maybe a month old

random overheating solved but need thoughts

Reply #7 – September 24, 2014, 07:35:58 AM

Wow...look at that. Haven't actually witnessed it myself before.
If you had a built-up hotrod with a 3 or 4-core Northern or Griffin super-duper huge thick radiator...you'd want as much flow as possible to take advantage of all that surface area. With a run-of-the-mill radiator, the water could pass through quick enough to not really transfer any valuable amount of heat.

Depending on what temperature you wanted...that big radiator + low temp stat / no stat at all might make the engine run too cool, that is if you're looking for fuel mileage or passing emissions.

random overheating solved but need thoughts

Reply #8 – September 24, 2014, 10:34:54 AM

just noticed my tstat housing says pn starting with "E9"

random overheating solved but need thoughts

Reply #9 – September 24, 2014, 10:43:10 AM

oh ,,,,,,,
well my new tstats working but....... it came with no fail safe feature so like many I drilled my little hole.
I make my own gaskets and this one was reused. I total forgot to cut out a notch in the gasket for the bleed by fail safe..... oh well.

random overheating solved but need thoughts

Reply #10 – September 24, 2014, 03:14:07 PM

I wouldn't sweat it...a 1/4" or smaller hole isn't gonna do much for you anyway.
If you bought a decent stat, it should well withstand the test of time.

See, this is what's great about the full digi-dash! If you start overheating or lose oil pressure...instead of the short beep tone you hear when switching displays, you'll hear a long beep and it will immediately toggle to the problem reading. It'll get your attention REAL quick and you'll be in instant panic mode

. Perhaps you have been there already. I know I have. Went around an on-ramp, oil must have been just low enough, apparently sucked in some air very briefly. Motor's fine...and I shut it right down and coasted to the side. Was scared to death. Started back up fine. But yeah....many miles of nothing and BEEEEEEP, you react like sitting at the tree on a dragstrip!

random overheating solved but need thoughts

Reply #11 – September 24, 2014, 03:20:36 PM

That thing was really stuck open. Probably because of the overheating.

random overheating solved but need thoughts

Reply #12 – September 24, 2014, 07:49:21 PM

Drilling a hole does not make a stat FAIL SAFE!! A fail safe stat locks open when it fails. When looking in a radiator of a running car with the stat open. The flow should not be strong across the core. While watching the flow it should dribble across the core and fall like a water fall. If it is strong and flows like a fire hose the core is plugged or restricted. Having an open or missing stat is bad because the cooling system needs restriction. If not the car over-cools and runs hot. You need a stat to slow down the coolant so the fan and radiator can remove the heat from the coolant. Hope this helps.

random overheating solved but need thoughts

Reply #13 – September 24, 2014, 08:18:15 PM

i didn't say the flow was strong,, I said it was like a water fall.
.... just as you said.

random overheating solved but need thoughts

Reply #14 – September 25, 2014, 02:55:49 AM

The 86 Gt that we bought recently in Idaho was running a bit warmer than I was comfortable with once we got to Az. so I went to a 16lb cap instead of the stock 13lb cap.

Once you have replaced that stuck open stat with a new one you might try that if the car tends to run warm. If that doesn't work my guess is that it might be radiator or fan clutch time.
Ron