408 still overheating :/

[furrystump]

Here's a thought, I have heard of the coolant moving to fast. It doesn't have enough time to shed heat while in the radiator. It's a long shot, but I have heard of it before. Sorr missed where it was mentioned above.

 

[12many]

That's a theory floating around, here's a guy with a too hot situation, with a n even worse environment (engine under doghouse with less that optimal flowthrough) who just about replaced everything, testing every component every which way possible, all was good, all the while running a new 6 vane Mopar Perf pump. Was advised to run an 8 vane w/plate to move the coolant, and problem was solved. YMMVvintage-vans.forumotion.com/t52684-runs-hot-out-of-ideas

 

[furyus2]

I haven't seen any mention of the electric fan cfm. I think they need to put out close to 4000 cfm. Correct me if I'm wrong. And doesn't the underperforming electric fans become an airflow obstacle? What did the shroud look like? If it's tje type that's a shallow box with just a hole for the electric fan, they are also an obstruction. Put a mechanical fan blade, and shroud on it first. Mine was 18 inches in diameter. Then make sure you have a hood to core support seal. It keeps from pulling the hot air back in. Almost 95 percent of the time when i read about an over heating issues, an electric fan is involved.

 

[T56MaxTorq]

Some things that haven't been mentioned:

Are you running a 50/50 mix of distilled water and glycol? Everywhere I go in Europe I've only seen unmixed antifreeze. You can go upwards to 75/25 water/glycol if you keep it in the garage. This will help transport heat.

There is a product called "water wetter" that helps remove bubbles in the system and will help transport heat.

Is your lower rad hose spring full length?

Are you positive that the system is holding pressure? It must hold the pressure indicated on the cap. The hoses should be swollen when at temp. Not limp. If it vents at 8 psi, you'll never get it to stay cool because it's boiling.

Never run an engine long-term without a thermostat or a gutted thermostat. It takes the engine longer to warm up or even warm up at all. Increased wear is not what you want in a 408 that already sees increased wear vs stock stroke.

You need to change the oil if it hit 250+ maybe even going with a synthetic oil. It holds up better to heat breakdown and wicks heat better as well.

I'm in favor of mechanical fans with a big fat shroud and the griffin radiator. My fan is even underdriven...

I completely agree with lowering underhood temps by wrapping headers, and using a scoop or some other hood vent. It's hard to take outside temps and push it through a radiator and efficiently cool it down if the underhood temp is hotter than the coolant.

 

[AJ/FormS]

Some things that haven't been mentioned:

Are you running a 50/50 mix of distilled water and glycol? Everywhere I go in Europe I've only seen unmixed antifreeze. You can go upwards to 75/25 water/glycol if you keep it in the garage. This will help transport heat.YES!,Water is the best, but you need to protect the water pump seal, and of course "Keep it from freezing" lol

There is a product called "water wetter" that helps remove bubbles in the system and will help transport heat. For me this is a last resort and is very expensive, especially when you get a leak. Really this overheat should be an easy fix

Is your lower rad hose spring full length?

Are you positive that the system is holding pressure? It must hold the pressure indicated on the cap. The hoses should be swollen when at temp. Not limp. If it vents at 8 psi, you'll never get it to stay cool because it's boiling.If it vents that's true, but;he didn't mention venting. I run a 7psi cap no problem.

Never run an engine long-term without a thermostat or a gutted thermostat. It takes the engine longer to warm up or even warm up at all. Increased wear is not what you want in a 408 that already sees increased wear vs stock stroke.Except for test purposes

You need to change the oil if it hit 250+ maybe even going with a synthetic oil. It holds up better to heat breakdown and wicks heat better as well.Just cuz the water hit 250 doesn't mean the oil did

I'm in favor of mechanical fans with a big fat shroud and the griffin radiator.Me too
My fan is even underdriven...Mine too

I completely agree with lowering underhood temps by wrapping headers, and using a scoop or some other hood vent. It's hard to take outside temps and push it through a radiator and efficiently cool it down if the underhood temp is hotter than the coolant. That's very true

 

[nm9stheham]

Hey AJ,

I thought you had some holes cut in the back of your hood to vent the air out and keep fresh flowing through?

And BTW, the compression ratio thing is not that it is the cause per se, but it will create more heat that has to be managed. And AL heads will also take more heat out through the engine directly into the engine compartment than with iron heads, bypassing the heat flow path through the radiator. Turbos and headers also add more heat directly into the engine compartment that has to be gotten rid of and the regular cooling system can't do a thing about that.

From the symptoms described, it just sounds like things are getting heat soaked at a high temp.

 

[AJ/FormS]

Hey AJ,

I thought you had some holes cut in the back of your hood to vent the air out and keep fresh flowing through?

And BTW, the compression ratio thing is not that it is the cause per se, but it will create more heat that has to be managed. And AL heads will also take more heat out through the engine directly into the engine compartment than with iron heads, bypassing the heat flow path through the radiator. Turbos and headers also add more heat directly into the engine compartment that has to be gotten rid of and the regular cooling system can't do a thing about that.

From the symptoms described, it just sounds like things are getting heat soaked at a high temp.

Well a very long time ago when the combo was first assembled, I was as naive as anybody. So I had a bit of a heat issue, lol .Just a minor one. I was on a roadtrip, some 600 miles from home. I noticed that every time I stopped for gas, the factory 1969 starter had a hard time cranking it back up. Remember I'm always bragging on my fancy OEM gauges? Well it wasn't catching any overheat, but there was SOMETHING doing on. Well. I dug out the tool-kit and elevated the back of the hood, and the problem went away. And the rest of the trip was all good. Well except for the occasional whiff of gas. But with 465-A/C it wasn't a problem.
So then when I got home I had some detective work to do..... 465; you know; 4 windows down@65mph.
When I got home,ten days later, I had some detective work to do. I put in a mini starter,put the hood down, and Badaboom.

 

[72SwingerJosh]

I've used that stuff called wetter on a ford 460 that always ran hot and it dropped the temp 20 degrees and it never over heated after that. Some block casting don't have the best water jackets and still full of packed sand.

 

[Unconventional]

Dumb question here. Are there any bubbles in the fluid in the radiator while it's running? Or the presence of CO or other exhaust gasses? Just a thought. Sounds similar to the symptoms in my SBF in the California desert summer heat with a blown head gasket. A wee little bit of exhaust gas in the cooling system can really change temps.

 

[1974scamp]

Good idea nm9! Or just run the car without hood for some testing. When you then have lower temperatures at all speeds you know how to proceed. The fact that a lot of your changes didn't do anything to the temperatures makes me think that something fundamental is off.
I had a similar problem in my E-body (long gone) with a much lesser engine, but then it simply was the original radiator --> bad "connections" between the mesh and the water channels of the radiator.

Ok i did a test drive today without the hood and i closed the gap between the top of the radiator and the chassie with some rubber:

It was about 86°F outside temp. and the max. water temp. shown on the gauge was 210°F

But the test drive was still with the old water pump from the 318 (i will change again to the milodon high volume pump) and with just the electric fan without a shroud

I have about 50/50 water/fluid in there.

I think i will build a cold air intake maybe it will be better then

 

[T56MaxTorq]

Nice looking engine!

You absolutely need a shroud or a full size fan. Or a mechanical fan with a shroud. Only way to keep it cool at idle with no ram air.

Also, I can see that your radiator cap doesn't vent into a reservoir (from what I can tell) The reservoir is an important cooling component. As the coolant thermally expands, it vents out the cap into the reservoir. When the engine cools, the coolant cools and becomes less in volume. This induces a vacuum in the system and draws the displaced "extra" coolant from the reservoir back into the radiator. Your engine ends up sucking air instead and you've blown out all the "extra" coolant onto the road. So you're running your radiator with a quart or more less fluid. The top 2 or more inches of the radiator are probably useless.

I have an A body reservoir and I was in Budapest a week ago. Damn shame. You can adapt damn near any unpressurized style reservoir tho. I built mine from aluminum.

 

[yellow rose]

Nice looking engine!

You absolutely need a shroud or a full size fan. Or a mechanical fan with a shroud. Only way to keep it cool at idle with no ram air.

Also, I can see that your radiator cap doesn't vent into a reservoir (from what I can tell) The reservoir is an important cooling component. As the coolant thermally expands, it vents out the cap into the reservoir. When the engine cools, the coolant cools and becomes less in volume. This induces a vacuum in the system and draws the displaced "extra" coolant from the reservoir back into the radiator. Your engine ends up sucking air instead and you've blown out all the "extra" coolant onto the road. So you're running your radiator with a quart or more less fluid. The top 2 or more inches of the radiator are probably useless.

I have an A body reservoir and I was in Budapest a week ago. Damn shame. You can adapt damn near any unpressurized style reservoir tho. I built mine from aluminum.

If you can get the fan close enough to the radiator, you don't need or want a shroud. Some shrouds can cause air to stop getting past the fan at higher road speeds.

I don't run a shroud. I don't need a shroud. I cruise at 175 and go 180 at stop lights on 103 degree days.

Not a fan of electric fans either.

 

[T56MaxTorq]

If you can get the fan close enough to the radiator, you don't need or want a shroud. Some shrouds can cause air to stop getting past the fan at higher road speeds.

I don't run a shroud. I don't need a shroud. I cruise at 175 and go 180 at stop lights on 103 degree days.

Not a fan of electric fans either.

Only pulling air through 1/2 the radiator is enough? I wouldn't think so on an engine with much more power. But, to each their own. I don't think this gentlemans setup would cool my engine, or his 408.

IMO, I would put the fan on the front if you can run it as a pusher and put the mech fan back on with a shroud. Mech fan moves a lot more air than the electric fan shown. you're also trying to cool down engine components as well, not just remove heat from the radiator.

 

[yellow rose]

Only pulling air through 1/2 the radiator is enough? I wouldn't think so on an engine with much more power. But, to each their own. I don't think this gentlemans setup would cool my engine, or his 408.

IMO, I would put the fan on the front if you can run it as a pusher and put the mech fan back on with a shroud. Mech fan moves a lot more air than the electric fan shown. you're also trying to cool down engine components as well, not just remove heat from the radiator.

How does it only pull air through half the radiator? When the fan is close enough to the radiator, a shroud can be a detriment.

 

[T56MaxTorq]

How does it only pull air through half the radiator? When the fan is close enough to the radiator, a shroud can be a detriment.

Look at his photos. The fan only covers 1/2 the radiator. without road speed, no cooling in that area.

 

[yellow rose]

Look at his photos. The fan only covers 1/2 the radiator. without road speed, no cooling in that area.

It's an electric fan. Unless there is a picture I didn't see.

 

[AJ/FormS]

If you can get the fan close enough to the radiator, you don't need or want a shroud. Some shrouds can cause air to stop getting past the fan at higher road speeds.

I don't run a shroud. I don't need a shroud. I cruise at 175 and go 180 at stop lights on 103 degree days.

Not a fan of electric fans either.

180 at stoplights? lol.
I call bs. no BS! That would take 7000rpm and a 2.45 rear and and something like 20% overdrive. Not to mention a really special engine
Now I'll grant you the your engine is special, and even that you might have the overdrive. But I surely doubt you would ever put a 2.45 in the back of any YR-owned car,lol. Well if you did, at least you wouldn't have the wind to deal with.......Surely you jest,lol

On another note........
Even if you shroud the whole thing, the electric fan mostly draws through a ring directly under the perimeter of the blades to maybe 50/60% back to the center. The center is more or less dead and that area outside of where the blades are, tends to not move at all,or even go backwards when stopped. So do the math on that. Suppose that fan is 16inches in diameter.That would make about 150 net sq inches of radiator exposed to the fan's airflo, or less than 1/3 of the gross available finned area, of say over 500sq inches I'd guess.
So now let's put it into gear.
Suppose that you had fully shrouded that fan. Now you expect ram air to drive thru the full face of the rad and exit out a 16 inch round hole of 200 sq inches,or 40% of the gross rad area.
Some 60% of that air,after it passes thru the rad,within say 1.5 inches, has to make a 90* turn and smash into whatever air column is trying to go supersonic, thru the fan. I just don't see that happening.
So to me a full shroud on just 1 fan is not a good idea. I would want that 60% bypass working for me.
So for me, I would never install electrics. Especially since a mechanical fan is so easy, and just flat-out works.
And there's plenty of other better reasons to not use electrics for a streeter, especially on a big engine sucking underhood heated air.I mean think about it: How far do you think you could run on a 200 or 300 or 400 degree day, compared to say just 68,lol.Do you think your body could get rid of that heat? Of course not; that's a dumb question.
And IMO, so is not ducting fresh cool air into any engine, nevermind a 408 streeter.
OP; I'm not calling you personally,dumb! The hot air intake is dumb. There is no way to control the AFR running like that. And if the AFR ain't right, then neither is the timing. So what you end up with is an impossible-to-tune engine.And a well-tuned 367 comes along and spanks you. Man that would suck! Unless of course the the entire car was in that 200,or 300,or 400 degree environment,lol, then I guess you might theoretically be able to tune it.

And on another note;
OP;How long do you expect your cooling system to hang together with a 24 psi cap?!

 

[T56MaxTorq]

It's an electric fan. Unless there is a picture I didn't see.

He posted today with 3 pics, it's the last pic. There is a significant amount of open space on the radiator that the fan doesn't draw air from, probably half the radiator. That's fine with road speed or a lower output engine, not a 408.

A shroud is important to fully cool all the rows fins. I don't know of any oem vehicle with an electric fan that doesn't use some type of shroud. But Im sure there may be a few.

If you have an electric fan with a shroud and it is causing a restriction at higher road speed, then you simply don't have a large enough fan with enough power/pitch in the first place.

 

[yellow rose]

He posted today with 3 pics, it's the last pic. There is a significant amount of open space on the radiator that the fan doesn't draw air from, probably half the radiator. That's fine with road speed or a lower output engine, not a 408.

A shroud is important to fully cool all the rows fins. I don't know of any oem vehicle with an electric fan that doesn't use some type of shroud. But Im sure there may be a few.

If you have an electric fan with a shroud and it is causing a restriction at higher road speed, then you simply don't have a large enough fan with enough power/pitch in the first place.

Cool. I'll go back and look again. I must have missed the belt driven fan.

 

[yellow rose]

180 at stoplights? lol.
I call bs. no BS! That would take 7000rpm and a 2.45 rear and and something like 20% overdrive. Not to mention a really special engine
Now I'll grant you the your engine is special, and even that you might have the overdrive. But I surely doubt you would ever put a 2.45 in the back of any YR-owned car,lol. Well if you did, at least you wouldn't have the wind to deal with.......Surely you jest,lol

On another note........
Even if you shroud the whole thing, the electric fan mostly draws through a ring directly under the perimeter of the blades to maybe 50/60% back to the center. The center is more or less dead and that area outside of where the blades are, tends to not move at all,or even go backwards when stopped. So do the math on that. Suppose that fan is 16inches in diameter.That would make about 150 net sq inches of radiator exposed to the fan's airflo, or less than 1/3 of the gross available finned area, of say over 500sq inches I'd guess.
So now let's put it into gear.
Suppose that you had fully shrouded that fan. Now you expect ram air to drive thru the full face of the rad and exit out a 16 inch round hole of 200 sq inches,or 40% of the gross rad area.
Some 60% of that air,after it passes thru the rad,within say 1.5 inches, has to make a 90* turn and smash into whatever air column is trying to go supersonic, thru the fan. I just don't see that happening.
So to me a full shroud on just 1 fan is not a good idea. I would want that 60% bypass working for me.
So for me, I would never install electrics. Especially since a mechanical fan is so easy, and just flat-out works.
And there's plenty of other better reasons to not use electrics for a streeter, especially on a big engine sucking underhood heated air.I mean think about it: How far do you think you could run on a 200 or 300 or 400 degree day, compared to say just 68,lol.Do you think your body could get rid of that heat? Of course not; that's a dumb question.
And IMO, so is not ducting fresh cool air into any engine, nevermind a 408 streeter.
OP; I'm not calling you personally,dumb! The hot air intake is dumb. There is no way to control the AFR running like that. And if the AFR ain't right, then neither is the timing. So what you end up with is an impossible-to-tune engine.And a well-tuned 367 comes along and spanks you. Man that would suck! Unless of course the the entire car was in that 200,or 300,or 400 degree environment,lol, then I guess you might theoretically be able to tune it.

And on another note;
OP;How long do you expect your cooling system to hang together with a 24 psi cap?!

WTH? You want me to post a video of it?

 

[yellow rose]

He posted today with 3 pics, it's the last pic. There is a significant amount of open space on the radiator that the fan doesn't draw air from, probably half the radiator. That's fine with road speed or a lower output engine, not a 408.

A shroud is important to fully cool all the rows fins. I don't know of any oem vehicle with an electric fan that doesn't use some type of shroud. But Im sure there may be a few.

If you have an electric fan with a shroud and it is causing a restriction at higher road speed, then you simply don't have a large enough fan with enough power/pitch in the first place.

Ok, help a blind onl man out. I don't see any pictures with a belt driven fan. I see where the OP says he had a shroud and took it off, but I see no pictures of it.

Thanks

 

[abodyjoe]

that pic that shows just a single electric fan. Is that how it still is? If so like stated it's not pulling enough air. Bunch of core not getting air flow while sitting. I wonder if it's even enough cfm. I'd rather see a belt driven fan with shroud then that single electric fan.

 

[gtsdude]

That fan might be ok at best for a drag car with limited run time, a street car? no way, won't cool a stock small block.

 

[gtsdude]

I have a similar radiator and use a chevy HHR fan, pulls a lot of air and cools my 340 pretty good. The only downside I had, like someone mentioned, was not enough air flow through the engine compartment when its hot out. I have the stock hood with no scoop so hot air has no where to go, I put some rubber flaps on the shroud and cut holes for increased air flow, seems to have helped. I got mine on rock auto, I think it was $38? IIRC Here is a part #DORMAN 620951

 

[AJ/FormS]

WTH? You want me to post a video of it?

Of course not; I believe you. lol
I'm having a lot of fun picturing it.

You know back in hi-school we did all the usual stupid teenager stuff.
But one day two of us put our bumpers together and had at it. Well the smoke was pouring out everywhere, and in the heat of battle I pulled a shift, and Kablamm I was into my buddies grill heehee. Me with my 70 Swinger 340, and he with his 69 Chevelle SS 427. There was no clear winner......