Hey folks!

I'm still trying to solve my "coolant coming out of the overflow tank" issue. It's only a dribble, but makes a mess and as best as I can tell it's when the 195 thermostat kicks open. I had the system burped (again) by a shop using a vacuum in addition to my attempts so I am pretty sure air is not an issue.

I replaced the thermostat with a new one (same temp, 195) in case it was defective. I then drove the car until the t-stat opened again, and although it did not burp it out, it was definitely wet up underneath the cap, despite my coolant level being close to the "add" range (since I've lost so much driving it this way). My best guess is that the 195 stat is too hot, and when it opens creates a pressure the pushes it into the overflow tank with such a force as to geyser it out. (Maybe I'm off....just conjecture.)

So, I went and got a new 180 thermostat thinking that maybe that is what was in there before I had this problem. (Quick recap for those not following the previous thread: drained coolant for manifold bolt job, t-stat was left out on counter for weeks and o-ring dried out. Went to parts store and asked for OE t-stat without checking what was in there.) Since replacing my t-stat last fall as part of reassembly, the car has had this problem. Anyways, I'm rambling a bit. Basically what I want to know is WHY would someone choose a 180 t-stat as opposed to the (OE recommended) 195? Just curious before I go put this 180 one in.

As always, Thanks in advance!

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Wesley A. Williams
MAFOA Newsletter Director

The engine was designed for the 195 stat and the ecm is set for the 195 stat, therefore you will get better economy. I still think you have a bad radiator cap or the wrong one, You should be able to get it to 230 deg without overflowing the reserve tank.
Don

[This message has been edited by ka4nkf (edited 05-26-2005).]

quote Originally posted by mtgjudge: Hey folks! I'm still trying to solve my "coolant coming out of the overflow tank" issue. It's only a dribble, but makes a mess and as best as I can tell it's when the 195 thermostat kicks open. I had the system burped (again) by a shop using a vacuum in addition to my attempts so I am pretty sure air is not an issue. I replaced the thermostat with a new one (same temp, 195) in case it was defective. I then drove the car until the t-stat opened again, and although it did not burp it out, it was definitely wet up underneath the cap, despite my coolant level being close to the "add" range (since I've lost so much driving it this way). My best guess is that the 195 stat is too hot, and when it opens creates a pressure the pushes it into the overflow tank with such a force as to geyser it out. (Maybe I'm off....just conjecture.) So, I went and got a new 180 thermostat thinking that maybe that is what was in there before I had this problem. (Quick recap for those not following the previous thread: drained coolant for manifold bolt job, t-stat was left out on counter for weeks and o-ring dried out. Went to parts store and asked for OE t-stat without checking what was in there.) Since replacing my t-stat last fall as part of reassembly, the car has had this problem. Anyways, I'm rambling a bit. Basically what I want to know is WHY would someone choose a 180 t-stat as opposed to the (OE recommended) 195? Just curious before I go put this 180 one in. As always, Thanks in advance!

A 180 isn't going to solve that problem. All it will do is give you a bit more room but a even a 215F stat shouldn't cause it to boil into the tank. Are you sure your radiator isn't clogged in the bottom rows and it's just overheating?

Replace your radiator cap with a GM cap (if you haven't already). The tank is lower than the radiator and if the cap leaks it flows into the tank. Any expansion then just sends more into the tank. I tried Stants, gave up and put in a GM. The Stants have been fine for the thermostat though.

Are you getting afterboil (fine until you shut it off and it blows into the tank...)?

As for the ECM, once the coolant comes into the 180 range it's pretty much in the normal operating range up through 240F. If you live somewhere that requires you to load the engine for a long time (long hilly climbs), then a 180 will let you start off at a lower coolant temp but in the end the coolant will still climb to the 220+ range. Start worrying around 230 (can you keep it there or get it back down) and panic at 250F because it is near the limit. No, 250F won't damage the engine but you better get the load off the engine....Around 260F, the 50/50 coolant going to start boiling...

[This message has been edited by TK (edited 05-26-2005).]

Silly question.. it's happend to me on both cars.. is the tank leaking? or the tube at the bottom? don't forget this stuff is nearly 20yrs old. I use 180 tstats.

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Denise, SE PA
Black 86 SE, Jasper 2.8, 5spd iszsu (Carlise 1st place winner stock highmile notchback 2yrs! ) 86 SE stock 2.8, Ttop, 4spd muncie, restored, Yellow

Wow, thanks for all of the quick and helpful responses.

Okay, first off I don't think there is a leak at all because the coolant pools on the top of the overflow tank, which is higher than everything else at that end of the system. Although, I've yet to actually witness it coming out the top (since I am driving when it happens), so maybe I can get someone else to keep the engine speed up in the driving range while I watch the tank as it warms up.

I think I will try a GM cap, though. Perhaps my Stant one is not working correctly for some reason (despite it being relatively new - 6 months). Are the GM caps discontinued or will a dealership have one? If someone has a part number handy without too much trouble I would be much obliged. Looks like tomorrow I stop and get another 195 stat and look into GM radiator cap!

Thanks guys...will finally post when I get this solved to help the next person when they search.

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Wesley A. Williams
MAFOA Newsletter Director

I cannot find a number for the GM cap, But I think the Stant would be ok.
Radiator cap----- 10231
Thermostat cap----10232

Also Stant has a new Thermostat out that is called a super stat and is supposed to be much better, It came out in April of 2005, But I have not found one yet. Ask for this number they might have it. 45819
Don

Could also possibly be a blown head gasket allowing compression into the coolant system. Just a thought. Maybe you should do a compression check.

This overheating stuff can be a real pain in the ol' "butt"
I had the same problem about 2 yrs ago, couldn't
track it down......turned out to be a combination of burping
which you've done and a bad rad. Cap. Make sure that you have the
correct cap !!! Good Luck

edit to add:
Also, go to Advance Auto, or Auto Zone an borrow a rad. pressure tester (free)
and do a pressure test on your rad. + your rad cap.

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[This message has been edited by 2000RagTop (edited 05-26-2005).]

I'm going to second the radiator cap. Make sure you are using a non-vented cap. The little disk on the bottom of the rad cap should be spring loaded and not dangle. I think Stant caps are okay, but be warned that the catalogs at most parts stores list the vented cap for the Fiero. This is wrong. Just ask for the same cap "non vented". If I remember correctly the part number is one less (read -1) than what the book says.

I just bought both new caps from the dealer so they are still available. There are two versions for the radiator. One with ears and one without (not that it matters).

quote Originally posted by mtgjudge: I replaced the thermostat with a new one (same temp, 195) in case it was defective. I then drove the car until the t-stat opened again, and although it did not burp it out, it was definitely wet up underneath the cap, despite my coolant level being close to the "add" range (since I've lost so much driving it this way). My best guess is that the 195 stat is too hot, and when it opens creates a pressure the pushes it into the overflow tank with such a force as to geyser it out. (Maybe I'm off....just conjecture.) So, I went and got a new 180 thermostat thinking that maybe that is what was in there before I had this problem. (Quick recap for those not following the previous thread: drained coolant for manifold bolt job, t-stat was left out on counter for weeks and o-ring dried out. Went to parts store and asked for OE t-stat without checking what was in there.) Since replacing my t-stat last fall as part of reassembly, the car has had this problem. Anyways, I'm rambling a bit. Basically what I want to know is WHY would someone choose a 180 t-stat as opposed to the (OE recommended) 195? Just curious before I go put this 180 one in.

Your complaint sounds like a bad cap. It is common for the aftermarket ones to cause trouble. I have never seen a GM one yet that did not work out of the box, I have seen many aftermarket ones that had issues.

The system is designed to operate with 15 psi on the system. The thermostat regulates FLOW, not PREASURE. The two are commonly confused. At 15 PSI, the coolant will not boil till about 260 degrees, but some coolant will push out and in with the heating and cooling of the engine.

The main reason that people use a 180 degree thermostat instead of the proper 195 thermostat is a thorough misunderstanding of modern cooling systems.

Ive used a 160* one since I built it with absolutely no problems. I just dont like the idea of engines getting as hot as they do these days. My engine is turbocharged too and runs like total crap with one any higher. Since I drive it mostly hard and fast, fuel economy was never an issue I also used a 160* in my 383 V8 Fiero and my 350 Corvettes.

I had a same problem with overflow, found out that it was a radiator the previous owner installed and the idiiot put some stop leak in it. Cause when I got a prelacement, found a bunch of crap n stuff that the stop leak settled at the bottom causing the lower rad channels to clog. I myself swapped to the 180 setup and like it better, especially when ya gotta contend with the inter-city traffic. My only problem now is that when my rad fan kicks in, it won't cut off until I stop the engine and let it chill. ( postin a note on that later)

Are you using the correct fill technique? Need to run without the Tstat to get the air out. Then install.
I run a 180, plenty hot.... everything under the hood lasts longer, more power, lower octane requirement, cooler trans, too. 195 is solely for emissions and slight fuel economy gain IMO.

On my truck towing I can pull a hill and maybe hit 190 vs starting out at 195 and hitting 205-210. Pulling 5500 lbs and no trans cooler either (just stock in rad).
90K and trans is fine.