Ok,

Do you have a mechanical fan or electric fan?

Mechanical fan-
1.Do you have a fan shroud on your radiator?
2.How far is the fan into the shroud?
3.Do you have a fan clutch that's installed? If so, how old is it?


Electrical fan-
1.Do you have power at the fan?
2.Do you have any relays that are built into the fan circuit? Are they burnt out?
3.How big is the fan and where's it located, in front of the radiator(pusher) or on the engine side(puller)?
4.Do you have a shroud on that electrical fan?
5.How old is the fan itself?


What thermostat do you have, 160, 185, or higher?


What kind of motor do you have? SBC, BBC, etc, etc? And, what is the current set-up of ignition on it? Is the motor properly tuned and when was the last tune-up?

* If the motor has timing issues, it could cause the coolant to overheat*


How much radiator fluid do you have within the radiator? Do you have a catch can for the spilled fluid?


Just some of the starting points we need to cover..

Dan

 

very good way to start the diagnostics this should be a sticky!

 

Eletric fan 1 12 in i hink. it works grate and pulls grate air flo .. 180 deg miled build sbc nothing crazy
Its odd to me becuase normally if its air flow then you could let the car idle in park and it would slowley clime .. But doesent ... Not even in park reved up cant get to even hit one 180 i watch the guage slowley come up and hits 180 the i can watch it fall back to like 160 everything it just peachey


Normley thats when it would over heat is on traffic around town and stop and go but everything is just grate even driving hard

My problem

Onley on the freeway at 75 for two or 3 miles its already at 200 on hot califorina days 210 at most but wount go higher..
So goong down the freeway 75mph 3200rpm with eveything hummming just grate watch the go up 200 210 ..... Now i just drop it in nutral and coast the motor just idleing now going 55 idle ..

The drop it in gear and whammmm stright from 210 down to 180

The alll over again

...bit not the case around town
Its lilke at a 75 there a dead air poket or the wated pump is pumping to fast

The radaitor was just cleaned at a rad sho
Helped but not fixed

I was wondering if chaning the rad cap from 16lbs (what i have now) to somethong different would help

 

Sorry for alll the typos
Dang smartphone keyboards

 

FUNNY..... I was able to comprehend everything you said

Eletric fan 1 12 in i hink. it works grate and pulls grate air flo .. 180 deg miled build sbc nothing crazy

It sounds like you have a puller fan instead of a pusher, got it. Do you know the MFG of said fan and how old is it?

The 1st thing off the top of my head is that at idle, everything is nice as it should be, but I'm thinking that at highway speeds, something is obstructing the flow of air into the opening of the radiator. Now, I could see that if you had a pusher fan it would do that at highway speeds but, I would need to see a picture(s) of what your set-up is right now.

Do you have a mechanical fan and shroud available? I'm thinking that that electrical fan isn't helping as much as you think. This is IMHO but need others to chime in on this..

You mentoned that you took the car to the shop. How old is the radiator and what kind is it, brass or aluminum?

What is your antifreeze ratio?


Dan

 

It might also help to get the size of the water pump and crank pulleys.

edit
******************
at 3200 rpm you are spining that motor and if the water pump is overdriven - it is possible to push the coolant around too fast and not let it cool down before returning to the motor.. you may have a couple of issues that will all work against you.

Also - what are you running in the radiator, water / coolant / water wetter....

 

Where is the fan mounted? inside or outside the engine bay?
Also, a single 12" fan isn't going to cool much sitting still in most cases.

I run twin 11" fans and had to build a shroud to get it to maintain proper temps.

 

Your lower rad hose may be collapsing at the higher speeds?

 

The fan os a pull fan and it pully really well i can stick my hand out the drivers window and feel the hot air from it

the problem that I am having is that it only overheats on the freeway

it will not overheat at night when the temperature has come down a little bit on the freeway
and it is a 15 inch fan
Really cool junk yeard find for 15 bucks
Looked the same fan up at autozone 395.99

 

And will not get over 180 on the hottets days driving hard in traffic around town
Or in the drive way

It have to be that the water pump pully is spinning to fast
That would over heat it on the freeway and make it run nice and cool around town
And the rad was cleaned out buy a local shop i took it to it is a copper rad

 

I would like to know the chemistry behind a radiator cap to high of presser to low of a presser
If anyone knows

 

The cap pressure allows the coolant/water to stay liquid at higher temps then if it was an open system - once the pressure gets too high and exceeds the cap rating - it will open and flow into the overflow tank...

Looking at your pics - It appears that your fan it right up against the radiator - I think I see some spacers (maybe cardboard) between the fan and the edge of the shroud... if that is the case - your not moving air through the entire radiator - only the section that open to the fan - I would suggest removing the filler between the fan and the shroud and let the air move - at Fwy speed you are moving more air through the radiator than the fan will pull - so what you appear to have is the fan/spacers is preventing full air flow....

let me know if this does not make sense - I work in Chino and can talk on the phone - I'm not an expert - but I can offer an opion... Greg

 

Sweet thinkks

I put the card board there thinking it would act like a more officiant fan shroud
Stopping the air from being pulled around in the engine compartment
so I put it in and it did not make a difference I just haven't taken it out yet the fan is mounted 1/2 in or so from the rad

 

Thats what i thoight about the cap
If thats the case then why different caps .. I for some reason I'm still leaning towards a water pump pulley spending too fast not alloweing the coolent to cool down before it goes back in and im rinning 50 50 with water wetter

 

Just saw this - what are the diameters of the crank and water pump pulleys?

 

Like I said - I'm not an expert - but It appears that you have a mechanical shroud and an electric fan - the fan should be set back enough so that - in conjunction with the shroud - it is able to pull air through the whole surface of the radiator.

Curious - were you having issues with the mechanical fan? - Also - what are you running for coolant?

 

running water with the GM Dex Cool red coolant
rebuilt motor and when everything without came across a cheap fan and I put it in I still have the mechanical crank pulley measures 7 in 3 quarters water pump pulley measures 6 inches I put the mechanical fan shroud back on to hide electric to give it a cleaner look

 

crank pulley measures 7 in 3 quarters water pump pulley measures 6 inches

So your water pump right now is "under driven".

Divide - pump pulley / crank - a 7 1/4 pump with a 6 3/4 crank = 1.07 or over driven.....

Don't forget - if you change the pulley sizes more than likely you will also need different belts..

6 / 7.75 = .774


So its overdriven instead of under driven. I would try a smaller water pump pulley. Its spinning about 25% faster than your crank. SO it might be caveatting. Ive had first hand experience with this on hi rpm Honda 4cyl motors, that road race and are hanging there rpms up around 6-9k for 30+min. going from a 28 tooth water pump pulley to a 26 tooth pulley make a good bit of difference.

 

So your water pump right now is "under driven" - so I would not think it is the water moving too fast.. I'd drop the mechanical in - but make sure it is "in" the shroud - but not up against the radiator.. see what that does for you..

BTW - did you make sure all the air was out of the system when it was put back together? if not - raise the front end (i parked my rear tires in the gutter and the front on the driveway ( I have a slight incline) - with the cap off - run the motor till the thermostat opens.. jut be careful.

 

yeah I've been doing all that it's not a huge issue but it would be nice to keep the temperature under 200 while on the freeway maybe I need to speed up the ratio how did you figure the ratio of the pully

 

Divide - pump pulley / crank - a 7 1/4 pump with a 6 3/4 crank = 1.07 or over driven.....

Don't forget - if you change the pulley sizes more than likely you will also need different belts..

 

I was debating on putting metal mechanical San back in and trying for a while I just don't like it there way too loud and I don't have a fan clutch either for the mechanical fan

 

My 2 cents is make sure no air in system. Going down the freeway you dont need the fan. Is it a high flow water pump. I have always thought if overheats on freeway is the radiator. Change to a 2 row aluminum.

Don

 

yeah I was hopin avoiding buying a new radiator but that looks like what I might have to do

 

ONe other thing to check - is your thermostat.. could you have a 195 in there?

Also - where is the sender for your temp gauge? - Different places will give you different readings.

 

The temp sender is next to the thermostat

 

That what i think it is
it's smaller pulley will slow it down or speed it up
I think a large pully would slow it down

a small polley will speed it up

 

All this because the car is running at 200 on the freeway? I guess I'm not up to date but is 200 really over heating for a small block? I would have been more concerned with the motor running at 160. At 160 I think you may have problems burning today's gasoline efficiently..

JMO

 

IMHO - nope - I run mine around 190/195 with a 180 thermostat.. but the OP said his will run up to 210 and maybe higher if he let's it.. so we are offering some help....

 

You right A Smaller one

 

Sorry I ment to say smaller crank pulley, or larger water pump pulley. My specification was a little off. Sorry. But either way I think your over spinning the water pump.

 

Yes it will because at 3500 rpm i think the pump is spinning to fast there for water in then out too fast


So i need a larger water pump pully

Or smaller rank