No coolant flow through radiator?

92saturnsl2

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Nope. A stuck-shut thermostat will give plenty of heat but the car will overheat since it has no access to the radiator. There are two cooling loops, one for each side of the 'stat, and the heater core gets the bypass loop from the closed thermostat.

OP should drill a tiny hole (1/16") in the top of the thermostat flange. This will give another avenue for air bubbles to escape through, and potentially allow better coolant flow behind the thermostat pebble to better signal it with temperature.
I actually did this on the second thermostat before installing it. An old-timey mechanic once told me that trick, drill a 1/16" hole toward the outside of the thermostat on cars that are troublesome to bleed. Seems to have made no difference.
 

92saturnsl2

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I have yet to figure this thing out, I'm still running about 15 degrees too hot. I drove it to work today (about 70 miles round trip) and it's exhibiting the same behavior. Runs about 205F highway cruising or idling, radiator fans on the whole time. If I climb a big hill where I'm on the throttle heavy, it will jump up to 210-215F, which is about 2/3 the way up the gauge. Lower radiator hose is still cool to touch after driving.

I've verified the cooling temp sensor is good, and both the gauge and ECU readout (gauge reads off a separate sensor) agree with each other.

I purchased one of the Lisle spill-proof funnels, my next step is to give bleeding another go. If that fails, I'll try the water through radiator test to check for flow, and replace radiator if necessary. This cooling system in this rig has been pretty meticulously maintained, if there were some kind of blockage in the radiator it would sure surprise me. But it is an aftermarket unit that was replaced several years ago, so anything is possible.

Can anyone think of anything else I should be trying?
 
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Pull the upper and lower radiator hoses and run water into the top hose nipple. Water flows to bottom hose nipple then, you’re radiator is clear. Could be that your water pump is getting ready to give it up.
 

92saturnsl2

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I hope there's still some folks subscribed and willing to help with this! Update and recap:

Despite a couple thermostat replacements and thorough bleeding, nothing has helped. I can drive the car 100 miles with no overheating, but it'll run at 205F idle/highway cruising, and creeps up to around 215F going up hills or when there's a moderate load on the engine. That's going off ECU readout via a OBD2 scanner. That puts the needle on the gauge about 2/3 which is too high, normal should be a touch under 1/2. Have tried replacing coolant temp sensors, same result.

Today I decided to gut the thermostat. When you buy a thermostat for this car, you get the whole engine inlet housing with integrated thermostat as one piece. It's possible to cut the thermostat element out and just slap on the housing, so that's what I did.

I used the same exact coolant fill bleed procedure as before. Car warmed up as quickly as it ever did just sitting in the driveway (no airflow through radiator), and when it reached about 203F, the radiator fans kicked on just like they did before. This time, instead of peaking at 205F and staying there with cooling fans running continuously, within about 5-10 seconds the temp dropped to 195F and the cooling fans kicked off. If I let it sit idling, it would repeat that cycle, go to ~203F, cooling fans kick on, back down to 195F and repeat. This is how it's supposed to work. The cherry on top is that the lower half of radiator and lower (radiator outlet) hose is hot this whole time, whereas before it was cool to the touch.

I suppose this indicates bad thermostat? I find that crazy as I tossed the old one (in this effort) and tried TWO new ones. Should I go with an OEM thermostat this time? I did notice a lot more bubbling during engine warm-up, is it possible the lack of thermostat caused the cooling system to bleed more effectively? Thoughts?
 
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I would guess Flow limited through the radiator either by the rad itself or worn WP impellers or a combination of the two.
What prompted the service to begin with?
 

92saturnsl2

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I'm happy to report that I've solved this puzzle. It was the thermostat.

Since the issue went away when I removed the thermostat element completely, I began to suspect the aftermarket thermostat. I decided to order an OEM thermostat from the dealer which took a few days. Should have done that to begin with, it was only about $5 more.

Swapped it out for the OEM t-stat and by golly, works like a charm now. Cooling fans kick on at 203 and within seconds, temp drops down to 195. Lower radiator hose gets warm as does bottom half of radiator now.

So having tried THREE Motorad thermostats, I can conclude they are either the wrong opening temperature (all aftermarkets for this engine advertise 180F opening temp, which they claim is OEM temp), have a major design flaw, or missed some essential details when they copied the OEM. The only big difference I can see visually is that the OEM thermostat has some kind of deflector on one side of the element; not sure what that is for. Anyone care to venture a guess? See photos, Motorad (aftermarket) on left, OEM on right.

I've been buying aftermarket parts for a couple decades now and my experience has been that they generally compare poorly to OEM in quality and longevity, but this is the first experience I've had where one has failed the function part of the equation.
 

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So you installed a thermostat with a different bypass disc/spring and expected similar results to the OEM stat.

3 times in a row, no less.
 
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When the thermostat is in the lower hose, a design issue exists where as it starts to open, cold water from the radiator will flow in and cool off the thermostat, even though the engine is hot. The design depends on a constant flow of hot water through the bypass hose reaching the sensing bulb so the thermostat continues to react to actual engine temperature. Anything that's not an exact copy of OEM could have problems.

The lower hose getting hot doesn't mean anything other than the car is not moving and the fan is not running, thus the radiator is unable to reject much heat. When the car is moving the lower hose should be near ambient air temperature.
 

92saturnsl2

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So you installed a thermostat with a different bypass disc/spring and expected similar results to the OEM stat.

3 times in a row, no less.
Affirmative. When I buy an aftermarket part that claims to work for my application, I assume it will function similar to the OEM. The aftermarket would not exist if this were not the case.

Nowhere did the box advertise that the cooling system would run 20 degrees hotter.

I did not have an OEM thermostat to compare to, so the difference in design was not evident until I went out and bought one.

Dealers typically don’t stock parts for 25+ year old cars, so aftermarket is often the only option if you need something quickly.
 

92saturnsl2

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The lower hose getting hot doesn't mean anything other than the car is not moving and the fan is not running, thus the radiator is unable to reject much heat. When the car is moving the lower hose should be near ambient air temperature.
It does mean something, heat versus the absence of heat in the lower hose (with car stationary) when using an aftermarket thermostat is a meaningful comparison.
 
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Good to see you got it figured out, and that's an interesting difference you found.

I just looked at photos on Rockauto, and all of the thermostats except Motorad (including a Beck Arnley that is stamped "Motorad") have that baffle. I wonder if that has something to do with your issue.
 

92saturnsl2

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Good to see you got it figured out, and that's an interesting difference you found.

I just looked at photos on Rockauto, and all of the thermostats except Motorad (including a Beck Arnley that is stamped "Motorad") have that baffle. I wonder if that has something to do with your issue.
Interesting, that’s probably the culprit is the omission of that baffle. I bought one of the replacement thermostats at Autozone (Duralast brand) in an effort to try another brand and it was a reboxed Motorad, just my luck. I’ll be avoiding Motorad in the future, that’s pretty shoddy engineering (err copying) work on their part.
 
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