[madtexan]

Hi All,
This one has me puzzled. My GTO does the opposite of what most other cars do.. It cools when idling in N but creeps up when driving say 30-50 MPH even on 78 deg day.

car details:
Orig 400 YS block w RAIII cam w quadrajet carb. Auto trans 200R4

20" Mr Cool electric radiator set to come on at ~190 deg. Installed per Mr Cool instructions w provided shroud and then placed OEM shroud on top as you can see in pictures.

I think 180 deg thermostat.
30yo OEM style radiator. 3 core.
30yo OEM water pump.
I drove the car today and it heated up to abt 220 and then parked in driveway idling in neutral and dropped back to 180.

Any Ideas which part to change first?

[Goatracer1]

What do you have now for a thermostat? Engine has to run above whatever that temp is .

[madtexan]

I'm pretty sure it's a 180 deg thermostat.

My mistake on the electric fan model, It's a Flex-a-lite 180 black magic extreme 15" 3300cfm model mounted behind radiator. https://www.amazon.com/dp/B000CNHFNA...d_asin_title_4

[tstroud]

Mine acted like that when I had the timing too far advanced.

[65madgoat]

What about if timing is too retarded??

[Goatracer1]

You are more likely to run hot if you have too LITTLE timing than too much unless the engine is pinging.

[RocktimusPryme]

That’s somewhat common on electric fan conversions. Though you see it more with dual fan setups. Because there is too much surface area blocked behind the radiator to allow airflow through at highway speeds.

By all means check timing and stuff as others have said. I wouldn’t think from the look of that shroud it would be super restrictive but if all else fails you might place some shroud vent flaps in each of the corners.

I might also try it without the OEM shroud too just to rule it out.

[madtexan]

The electric fan shroud doesn't block radiator like some I have seen that are flat. It allows airflow from across the surface and it has a large amount of CFM, 3300, compared to others I have seen.

The mention of shroud vent flaps is something new to me. Do you mean cut holes into the electric fan shroud and place something homemade on the back side to prevent backflow?

Timing is well advanced with no pinging at all through accel range. I have a HEI distributor with custom timing curve ground into the weights that I saw in High Performance Pontiac mag back in the 90s.

I also recently started running Ethanol Free gas and it's only avail at 90 Octane if that makes a diff.

[RocktimusPryme]

So something like this. Scroll through the pictures and it will show them installed. They come pre installed on most of the high end dual electric fan setups. Most of those look like they are made out of a flat cookie sheet. I wouldn’t necessarily expect your shroud design limit highway air flow. But I guess a 15” opening isn’t huge and the symptoms sure point that way.

Most of the time when I see people put them in they just use a hole saw and pop a couple large round holes out and cover them with the little flap.

https://www.speedwaymotors.com/Radia...ck,527466.html

You can also just google dual fan setups and you will find some that come with them. Derale comes to mind but I’ve also seen them on stock setups. Like I said, exhaust all your other options first but if nothing else works……. I have very little conscious about these things but I know others aren’t always as ready to take saws to their items as I am.


The 30 year old stock style radiator might be something that could be upgraded.

[Squidward]

What size is the pulley on your water pump? Small diameter equals most coolant flow. Also, your coolant flow is a sum of 3 different flow paths: recirc, heater core, and radiator. Recirc is determined by the size of the hole from the intake to the timing cover. Heater core flow can be modulated by a heater control valve, etc. The radiator gets everything else, modulated by the thermostat.

I've become highly suspect of regular thermostats not allowing enough flow because they don't open far enough. I found that when I took my tstat out, I recovered a significant amount more cooling capacity. When I reinstall a thermostat, it will either be a high flow, OR I will drill holes in a standard tstat to allow more flow area.

[madtexan]

Originally Posted by Squidward

What size is the pulley on your water pump? .

It is the original OEM pulley size. These temperature changes haven't been happening with the exact same setup in the past so I suspect something failing.

Originally Posted by Squidward

I've become highly suspect of regular thermostats not allowing enough flow because they don't open far enough. I found that when I took my tstat out, I recovered a significant amount more cooling capacity. When I reinstall a thermostat, it will either be a high flow, OR I will drill holes in a standard tstat to allow more flow area.

I guess the simplest thing to do is change thermostat to high flow unit. Any recommendations on model.?

Car also has the OEM Pontiac intake manifold.

[Squidward]

I am currently not running a thermostat while I have been troubleshooting my own issues. I plan on getting one soon. I hear Robert Shaw high flow stats are good. I have no experience with them yet.

[RocktimusPryme]

I use the Stewart EMP high flow models. They were originally called the “Robert Shaw” design. I trust them way more to open when they are supposed to.

[madtexan]

I opened the thermostat housing and saw the existing stat was stuck partially open when vehicle was cold (failsafe model). I ordered/installed a Steward high flow 160 deg and saw the water started flowing at 160 and electric fan came on at 180. Temp fluctuated and highest point was ~195 on 85 deg day during driving 40-50mph. ...

I am surprised it came up that high. Will test on a typical 95 deg Texas day this week.

[nUcLeArEnVoY]

^^ All a thermostat does is set the minimum operating temperature of the engine. It's the capacity and efficiency of the cooling system and its components that determines if the thermostat temperature is actually able to be maintained. Unless the ambient temperature is low, it's going to take a beefy cooling system on a low comp engine to maintain a 160 degree operating temp, especially once you're at sustained higher RPMs on the highway.

[android 211]

You exchanged a larger mechanical clutch fan for a smaller diameter electric fan. Of course it does better at low engine speeds because heat output is low enough for the fan to handle it. On the highway the engine is putting out too much heat for the fan to handle it. My '69 has a/c and a 4 core brass radiator. Even when its 90 out the clutch fan keeps the temp below 220 in traffic. I have the factory 7 blade fan and a HD Hayden clutch.