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Discussion Starter · #1 ·
hey guys so I have a 250 with a offy intake and 4bbl holley 390 carb and I cannot figure out why it is running hot.
it has a brand new thermostat that I tested a new radiator and a new HI flow water pump. I have flushed the whole cooling system.
even while cruising it stays at about 200 degrees but when stopped will quickly climb to 230
I cannot figure it out so any help would be great
 

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I do not believe it is common, but there is the scenario where high flow water pumps move fluid too fast for it to transfer heat properly in the radiator. Exasperated by a larger "performance" radiator. Also could be causing air pockets in the water jackets.

Another item, what is the factory operating temperature range for the motor? Is it a late '70s smog engine designed to run as hot as possible for emissions reasons?

What do the spark plugs look like? Could it be running super lean at speed? Maybe a timing / air-fuel issue?

Just some thoughts...
 
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Discussion Starter · #7 ·
I do not believe it is common, but there is the scenario where high flow water pumps move fluid too fast for it to transfer heat properly in the radiator. Exasperated by a larger "performance" radiator. Also could be causing air pockets in the water jackets.

Another item, what is the factory operating temperature range for the motor? Is it a late '70s smog engine designed to run as hot as possible for emissions reasons?

What do the spark plugs look like? Could it be running super lean at speed? Maybe a timing / air-fuel issue?

Just some thoughts...
It was running hot before the hi flow water pump, I was hoping it would fix the issue but no change in temp.
it’s not a smog engine it’s a 72
I have it timed to 9btdc at 500rpm
I’ll check the spark plugs, I did just adjust the mixture screws to top vacuum
 

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1969 Nova . . 2dr . . Chino Valley,Az USA
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Hi ShaneT ..................

I also am using an OFFY Intake & Holley 390 carb . (Both bought new from Summit ; installed back in
2017) .
But , I also am using a 'stock 3 row (V 8 , brass ) radiator .......... stock for my 250ci engine , with the stock
Factory A/C = H D cooling package . I also use a GM 7 blade 'Fixed Fan Blade' . . . . . and , using a SW manual reading 'water temp gauge' . . . mounted in the
drivers side of the block (towards the rear mid section on the motor
(in the rear ,drivers side, freeze plug area) .
I've been running my temp gauge in that position for 23 + years . I also use my stock 'idiot light - in the dash' . . . . . (which has ONLY came on ONCE ,
during all that time) .
Then , on my "thermostat housing" ; I mounted a manual reading "MOON water temp gauge" .....................
.............. I really like too know how HOT my car does run (even here in Arizona) .

# 1. - - Moon Direct read water temp gauge



# 2. - - thermostat mounted water temp gauge (same as # 1. ) .



# 3. - - under dash water temp gauge



......................................................

so , my 250ci motor , Does NOT run HOT . . . . . . . (it's my original stock engine ) ; with only bolt on up-grade parts . (plus , I still have an A/C mounted
condenser . . in front of my radiator ).

Does your Fan blade "pull air through your radiator" . . . . can you put a sheet of notebook paper
in front of your radiator , and will it stay there . . . . ? ?
Have you checked if your radiator hose is (maybe) collapsing together = reducing water flow . . . ? ?
Check the lower hose . . ? ?

Go and buy you an "INFRED TEMP GUN " ...............

# 4. - -

Camera accessory Audio equipment Gadget Font Auto part


too use for checking u'r "readings on u'r temp gauge" ............... also , take readings at both
radiator hose connections (on u'r rad) .
Do you know what your water pump pulley diameter is . . ? ?
what size rad. cap do you use . . . . . ( pounds ) .

just asking . . . . . .

jim
 

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I'm not familiar with the inline engines but that sounds like very little timing and could be contributing to your heat problem.

Second though is do you have a fan shroud on the radiator?

Third though is does your fan clutch lock up properly?
 

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1969 Nova . . 2dr . . Chino Valley,Az USA
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I'm not familiar with the inline engines but that sounds like very little timing and could be contributing to your heat problem.

Second though is do you have a fan shroud on the radiator?

Third though is does your fan clutch lock up properly?
Ok ................

Most (but not all) Nova L 6 motors . . . did not use a fan " shroud " .
Like my 69 250ci engine . . . WITH factory A/C . . . does not have a fan "shroud " . (no room , for one) .
But , when you order a/c (with any engine) . . you automatically 'got the Heavy Duty Cooling Package'
(RPO - V01) ; which included some extra parts (on the L 6 motors) . Like a V-8 radiator , (3row brass)
; a shorter
(6 cylinder - A/C ONLY - water pump) ; (a shorter 2 groove w/p pulley) ; a (6 cyl - only) -
Fan Clutch (very short) ; and a V-8 , 7 blade fan blade ( part # - 3947772) .

BUT , no fan shroud . . . !

Also , most (maybe special order) . . L 6 motors , use a "direct drive 4 blade , fan .
Even L 6 engines with the P/S option (N40) . . . just had 4 blade fans ; with no fan clutch .
Then , if that was on an L 6 engine ............................. it was most likely added over th' years .


then , Timming . . . .
I'd re-check that , can't hurt anything .


later , jim
 
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Twisted6 ........................... always a very cool car & VERY COOL engine , Thanks Larry .

. . . jim
 

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I do not believe it is common, but there is the scenario where high flow water pumps move fluid too fast for it to transfer heat properly in the radiator. Exasperated by a larger "performance" radiator.
There is no scenario where the coolant moves too fast to transfer heat, short of damaging the radiator. High coolant flow transfers more heat due to the fact that the radiator is as uniformly hot as you can get it. This maintains the maximum Δt across the entire cooling surface, which means maximum heat transfer. It also promotes more turbulence, which is a major contributor to heat transfer.
 

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1969 Nova . . 2dr . . Chino Valley,Az USA
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Apparently this car has not always run hot. What did you change last that made it run warmer? You changed water pump, radiator, and thermostat, all at the same time?
Really good question , Bob .................

Then , I'd have too ask - - (No Disrespect) - - but , did you mount your fan blade correctly .
(facing the right way ? ) .


I was at our local cruise night - earlier this summer - - - - - - - - and , was kinda 'surprise - when looking
at a car (Ford Mustang , early model ) . . . . and , saw that he (or someone) had mounted his 'water pump
Fan Blade , backwards .

it can happen ; just checking .

jim
 

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Then , going back ................................ I had asked this same question ...............................

back in post # 8 ....................... ( "Does your Fan Blade - Pull air through your Radiator" ) .

simple ..................

and , let us know how you got this 'solved'


jim
 

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Discussion Starter · #19 ·
Alright guys
Sorry I’ve been busy and hadn’t had a chance to check back in
I’m gunna try and answer all the questions

the fan is mounted correctly and does pull air. It’s a fixed fan so no clutch I do have a diy shroud on there but so it pulls pretty

as far as when it started running hot I don’t remember. But it for sure has since I put the holley 390 and offy intake, it might have been before too but I can’t remember
Once I noticed that it was running hot I first replaced the thermostat after that didn’t help, then the rad because it was also leaking and I knew it needed to be replaced anyways, but it didn’t help at all so I replaced the water pump and again no change.

so today I checked the plugs and to me it does seem a little lean but I don’t have much experience in reading plugs so here’s a few pictures on one
Hand Liquid Fluid Finger Gesture

Hand Finger Thumb Gas Nail

Finger Nail Gas Thumb Auto part

Finger Gas Fluid Auto part Nail

Hand Finger Nail Thumb Household hardware

Hand Finger Tints and shades Nail Automotive tire
 

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1969 Nova . . 2dr . . Chino Valley,Az USA
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say , would you have a picture of the fan blade , that you are using - - - - - a stock 4 blade fan . . ?

If so , look around (check some parts places) , (u-pick it yards) , and find / buy a 5 or 6 blade fan :
too draw more cooling air thur your radiator .

My car (had) a 7 blade fan ; with a fan clutch ) , now has a 7 blade fixed fan blade . But , I do have my
STOCK 3row (V-8) radiator (HD cooling , for A/C) . I still have that set-up ......... but , removed it because of
being 50 plus old fan clutch . I already had a "fixed 7 blade fan , that fit" . 18" dia .

I did buy both my 390 carb & Offy intake New from Summit ....................... but , I do-not have a
"running hot" issue .
I'd think it could be something 'simple' .................................

. . . jim
 
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