Cooling Issues - What to do next?

[davepl]

This isn't my truck, it's the ZZ502 disguised as a 427 in my stock-appearing 2+2 (call it an Impala, or just pretend its the big block in my GMC, it's a generic issue!).

I'm going to throw a lot of info out here in the hopes one of you wizards will have an idea. There must be something weird, because it shouldn't be like this.

Factory HD radiator (new), HD clutch fan (new), shroud (newish), so everything original is in place where it should be.

It runs, according to the gauge, about 215F. That's not the end of the world, but its not a controlled temp. I think there's a 190F thermostat, so it should be more like 195F. Plus if you get a warm day or stuck in traffic, it creeps up with no end in sight.

Last time I drove it I got home and the gauge read about 225F. With a temp gun I checked the thermostat neck and it was 210F, so maybe the gauge is a little high. Just before I shut it off the water in the lower rad hose measured at 180F.

Problem is I know it's hot because it pukes coolant out, about a quart, after an event like this. Rad cap held 15psi. I think whole system held pressure too but I have to double check.

The engine is older than the radiator and restoration. It wasn't rebuilt because it checked out fine and had only a couple of thousand miles on it anyway. Only thing I've noticed is that the water at the intake when I took the thermostat housing off was dark brown, yet every drop of coolant that I drained was bright green. So that's weird. Looks clean in the rad, dirty in the engine.

I'm putting a $400 BeCool pusher fan in front of the rad right now, but I seriously hate bandaids like that.

This car has never really cooled well with any engine/rad combination. Used to overheat with a 350 and 2-core sometimes, then with a 396 and 3-core, now with a 502 and 4-core. I wonder if the design of the front end might cause reversion, or whatever it's called when your rad ingests hot air that loops around from behind at slow speeds. But its still hot on the highway too.

I'm putting a 160F thermostat in today too, which isn't something I'd do if I was comfortable that it could control its temp at 190. Another bandaid.

I haven't seen bubbles or anything in the rad (downflow style) to indicate a head gasket leak.

Should I flush the motor out? If so, just water in the rad neck while running the engine until what's coming out the rad drain is all clean?

Thanks for any tips,
Dave

[Lee H]

How's the water pump? New, reman, old. A lot of the generic remans are marginal on a hard to cool engines, they just don't cycle enough volume and the high volume ones tend to just sit there and cavitate. Did the head gasket match up well with all the water passages? The thermostat will not regulate an engines normal operating temperature, just how long it takes to get there. Any gaps between the shroud and the radiator?

[davepl]

Originally Posted by Lee H

How's the water pump?

It's orange. I don't know much more about it, actually. I know the motor came with a reverse rotation short pump so I needed to swap it for an old school long water pump.

Originally Posted by Lee H

Did the head gasket match up well with all the water passages?

It was one of the early ZZ502s, and might have been in the late 90s. But it was Chevy-supplied Edelbrock heads (before they switched to their own label) and Chevy-supplied gaskets and Chevy-supplied block, so it should match.

I did stick a 1969 427/390 intake manifold on it and a Q-Jet to make it more original. That's a huge compromise on the intake ports (roval vs oval) but the coolant passages should be unchanged between all of the head styles, I think.

Originally Posted by Lee H

The thermostat will not regulate an engines normal operating temperature, just how long it takes to get there.

Can't agree there. A properly functioning car should operate at its thermostat open point (or close) and keep a reservoir of sufficiently cooled water in the radiator. Once it loses control of the temp, you're in trouble.

Originally Posted by Lee H

Any gaps between the shroud and the radiator?

No. I added hidden weatherstrip to keep it sealed up.

[davepl]

So here's what I did and here's what I found.

(a) I drained all of the coolant, filled it with clean water, and then I rinsed the engine until it ran pretty much clear.

(b) Installed a 160F thermostat. The old one says 180F

(c) Installed a 2360CFM pusher fan in front of the radiator, triggered by a 195F-on, 175F-off sensor in the head. I even used green wire and that old asphalt wire cover :-)

Drove it around. It's 85F and humid today, so not the most demanding scenario but not the easiest. It seemed to run around 195 on the gauge. The fan never kicked in.

Took it home and parked it, let it run. Eventually crept up to what looked like 220F on the gauge, then the new fan kicked in. About 3-4 minutes and it went back off, though the gauge barely dipped back to 210.

With a temp gun on the thermostat housing I see reasonable temps: 180F, 190F at most. Bottom rad hose now providing 160F coolant back to the engine.

The fan cycles off an on every couple of minutes at idle. Even my new factory cars do that, so I'm not too worried now.

If it holds up, I'm going to have to do the old "boil the sensor" game and make another table and probably add a resistor inline with the gauge sensor to calibrate it.

[chiefcfd]

I think you answered your own question. I think that motor has to have a reverse rotation water pump and clutch fan setup. The water is not circulating properly. Maybe someone else can shed more light on the subject. I know my Vortec crate motor uses the reverse rotation water pump and clutch fan.

[davepl]

Originally Posted by chiefcfd

I think you answered your own question. I think that motor has to have a reverse rotation water pump and clutch fan setup. The water is not circulating properly. Maybe someone else can shed more light on the subject. I know my Vortec crate motor uses the reverse rotation water pump and clutch fan.

No, you're confusing reverse flow (like the 90s LT1 and LT4) with reverse rotation of the water pump, which still maintains the same flow within the block.

There are no different big blocks that require different cooling paths.

[RenoKeene]

Did you 'burp' the system to get the air bubbles out?
Jack the right front of the truck up so the radiator fill neck is higher than the block. You should be able to run the motor enough to work all the bubbles to the radiator neck and out of the system.

[davepl]

Never thought of doing the 'lift the corner' thing, neat idea. I think, though, that with the bypass hose big blocks don't usually need it. At least I've only had air trapped in small blocks. I like the old 90s LT1 with the bleeder valve. Probably because they were prone to it do to reverse cooling, but it made things pretty simple.

Maybe I should invent the "thermostat housing with integral bleeder valve" :-)

[my67c20]

The other thing to remember is to not fill the system full when cold.

[Oxmarqt]

[/QUOTE]Can't agree there. A properly functioning car should operate at its thermostat open point (or close) and keep a reservoir of sufficiently cooled water in the radiator. Once it loses control of the temp, you're in trouble.[/QUOTE]

Your thought process is not 100% correct on this. I only mention it because there are many people doing LS conversions and also working on there regular, more modern vehicles, that might be misled by what you say.

My 2007 Chevrolet Silverado 5.3L has a 180* thermostat. The thermostat should begin to open at that temperature and be FULLY open at 206*. The cooling fan is not designed to come on until engine temp exceeds 220*

After the vehicle is shut OFF if the engine is greater than 214* the low speed fans will run for a about 60 seconds After 60 seconds, if the coolant temperature drops below 214* the fans will shut OFF.

Now to go back to the Old School engine even GM states in their manual for a 1969 that the thermostat should start to open 10* before temp marked on thermostat and be fully open 25* HIGHER than the temp marked on thermostat. In your case, based on the original 180* thermostat installed, that would mean fully open at approx 205*. At that point flow and fans maintain engine temperature.

Not trying to be confrontational but your 215* temp IS a controlled temperature but it appears to not be one you like or are happy with.

I would suggest putting a probe in the radiator, no cap actually in the coolant, and see what the readings are. that is the only way to get a true reading. Using the infrared, while convenient, is only giving you the temperature of the housing not the actual fluid.

**Side note - I also own a 1977 CJ7 with a 304. 190* thermostat and coolant runs spot on at 220* fully warmed up both on the gauge and with a probe. Basically the same number specs as the '69 manual states and the 2007 fans specifications list.

[Andy4639]

I have to agree with this. The temp on the thermastate is not the temp the motor should run at but what the operating temp is for that stat. A new vehicle runs at 210-220 which is normal operating temp for a computer controlled vehicle once warmed up. Putting the 160* thermo in your ride will not let it perform at it's best and will not have much heat in the winter time either.

The older cars ran close to this also but the general public thought the thermo was what the vehicle ran at and they all thought the temps where lower than they really where.
The infer red will give a close reading but as stated it will also show metal and outside temps to added to the liquid temp.
To me the vehicle in question seems to be running fine with the temps you posted. I suspect the gauge may need to be recalibrated.

[leddzepp]

Originally Posted by Andy4639

I have to agree with this. The temp on the thermastate is not the temp the motor should run at but what the operating temp is for that stat. A new vehicle runs at 210-220 which is normal operating temp for a computer controlled vehicle once warmed up. Putting the 160* thermo in your ride will not let it perform at it's best and will not have much heat in the winter time either.

The older cars ran close to this also but the general public thought the thermo was what the vehicle ran at and they all thought the temps where lower than they really where.
The infer red will give a close reading but as stated it will also show metal and outside temps to added to the liquid temp.
To me the vehicle in question seems to be running fine with the temps you posted. I suspect the gauge may need to be recalibrated.

I agree with this.

[davepl]

I still don't see it, so let me state my assumptions and someone can point out where I'm wrong or make an incorrect logical leap.

- The engine produces heat
- That heat goes a number of places (oil, air, etc) but primarily to the coolant
- The hottest coolant will be at the start of the upper rad hose, the coolest at the lower. It's possible heat from the heads gets deposited in the intake so it could be a couple of degrees hotter in the head than the thermostat neck, but let's ignore that as not relevant to this discussion.
- When the water in the block reaches the thermostat rating, it opens
- Coolant at or near the thermostat rating goes to the rad
- Rad cools it as much as it can given airflow and so on
- Cooler coolant enters the block from the bottom
- The thermostat cycles open and closed as long as the coolant coming from the rad is cool enough and it can make it to the thermostat still below its rating point ***

As long as the radiator is capable of shedding heat faster than the engine can produce it, the engine will run at the thermostat rating point. In reality it tends to be about 10F hotter than what the thermostat is rated at.

If you have a scenario where the radiator cannot provide coolant cool enough to bring the engine back down to its thermostat rating point, it's in "runaway" mode. The only thing that's going to determine how hot your engine runs at this point is how much heat it makes vs. how much the rad can get rid of. It's uncontrolled. That's not how its designed to operate.

And as much as I hate to be that guy, it'd take some pretty strong engineering arguments to convince me otherwise.

You can also look at modern cars. My LS7, from memory, runs a 200F thermostat and operates around 205F. If it gets above 215F, the fan runs until the temp gets back down to 205F or so. If it exceeds 225F or you turn on the AC, the second fan comes on. It's goal in all cases is to get it back to thermostat point.

And yes, 160F is too low. I'd rather it run a controlled 195F. In the 80s we all wanted the engine as cold as possible and 20/50W oil and other incorrect notions. You get less wear and better performance when the engine is hot. It wants cold air and hot oil (within reason), but we confused heat in the motor with heat in the intake air, even though former can impact the latter depending on your intake path.

All that said, I agree mostly with Andy4639. I believe the sender is either a mismatch for the gauge or at a minimum needs to be recalibrated. It's showing 20 or 30F higher than the temp at the thermostat neck. Fortunately I can add a resistor in line (as long as its fairly linear, and if you check the map/table of sensor ohms I posted a while back, it seems to be).

With the current setup it does require the pusher fan to stay controlled, but the fact that the fan cuts in and out shows its still in control. And it was 85F and humid and I just let it run at idle like traffic indefinitely to see what it would do.

[bonnieclyde100]

what i would do is take the stat out and see what the temp goes to. if it still goes over 200 you still have a cooling problem. i have a 195 stat in mine and it run between 195 and 205 . if i take the stat out it barley hits 150. the stat does control the temp by opening and closing to maintain a controlled temp. the number is not always exact but it shouldnt be to far off. sitting in traffic it will raise but it still shouldnt overheat if you have a good fan and all other cooling parts are write for your engine and there is no air trapped inside to hinder flow.

[bonnieclyde100]

is your gauge sensor in the intake or heads because if it is in the head it may say hotter because of the exhaust being so close. i just had the same problem with mine and i drilled and tapped the intake for a second sensor so now i have one for my engine computer and one for the gauge?

[davepl]

I don't think the head is much hotter than the intake. There's really nowhere for it to release heat between the head and the intake, or at least not much. I could see a few degrees but I doubt it's substantial.