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Overheats on Highway, cool at low speeds

34369 Views 66 Replies 20 Participants Last post by  knickick, 
4beers4me
Mild 350 with edelbrock 600 cfm overheats at 50 mph and higher. I can come to a stop and watch the temp guage go down. City driving is fine. Do I need to change jets and metering rods to run richer? Changing the timing hasn't helped any.

I thought my new AC was too much for the system but I have replaced thermostat, radiator, and water pump. Running a huge electric fan with shroud. Hoses look good.

Vacuum is running 21" at idle so it doesn't look like I have a vacuum leak. Not sure what else to do here besides carb.
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56owner
PULLER FAN ??

YOUR FAN IS PULLER MOUNTED ON REAR OF RADIATOR RIGHT?? PUSHER fANS DON'T WORK TO WELL.:

p.s. WITH ENGINE RUNNING WARM AT CRUISE MAKES ME WONDER IF LOWER RADIATOR HOSE IS SUCKING SHUT AT HIGHWAY SPEEDS. DOES YOUR LOWER HOSE HAVE A WIRE SPRING INSIDE IT??

anim_25:
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4beers4me
It is puller. Have to check on the spring. I thought of the spring before and let it slip my mind. I'll check that before changing the carburetor. Thanks.
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Jim '57
Electric fans can be wired to turn either direction. Have you checked to make sure it is pulling? I put a sheet of paper in front of my radiator and my fans blew it away instead of sucking against the radiator so I reversed polarity and they work great.
Jim
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auggie56
Fans aren't needed above thirty five MPH. How old is your radiator ? If it's old it maybe plugged.:confused0006:
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R
Either the radiator is restricted/plugged, or the thermostat isn't opening all the way.

I had a thermostat do that, it would open at normal temperature but wasn't opening all the way. The water temperature was fine up to 50-55 mph, but above that the faster you went, the higher the temperature went. Putting the old one and a new one in a pot of water on the stove verified the situation.
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4beers4me
There was no wire in the lower radiator hose. I made one out of a coat hanger and wrapping around some PVC pipe. This seems to have helped dremendously. I will try to get it out on the highway again this weekend to check it out.

I do have a new thermostat. If I drain the coolant again, I will still test the new one just to make sure.
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jwmbishop
:eek: A coat hanger is soft steel and will disolve in no time - the wire in the hose you buy has a very differnt metallurgy content! (but cool ingenuity)

I had the same issue with electric fan and 3 row alum radiator. Solved with a flat shroud (basically a two inch deep cookie sheet that fits the core and has a 15" hole for the 16" fan). This brings all the air thru the fan and keeps it spinning at highway speed even when not called by temp sw. (before shroud the fan was restricting when not spinning - enough heat would build in the radiator that by the time fan came on it was too late and not enough to cool both the heat stored in the radiator and the heat generated by the engine)

I doubt its the carb - bring er up to highway speed hit nuetral and shut down at tha same time (when safe to coast to stop) - pull a spark plug - if its bone white with specks of silver you are lean and it could be the carb - but I seriously doubt it. If you were lean enough to overcome the cooling system cruising you would have other lean symptoms - backfire, stumbles, blown head gasket, pre-ignition etc. - and it would be worse under throttle.

Unless of course you gots a blower on there.

Check your belts and pulleys - slipping could cause overheat and the higher the RPM the more percentage of slippage you can get! If the belt is all the way down in the v of the pulley it will slip no matter how tight you make em.
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55chevynut
Sounds like a thermostat Issue. Take It out and see If the temp goes down. Sometimes even a new stat will stick, you don't need one unless you drive It In the winter!!

Cliff
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Ari
It sounds like the thermostat is upside down.
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jwmbishop
55chevynut said:
you don't need one unless you drive It In the winter!!

Cliff
Click to expand...
Not true. Simply not true.

In a typical automotive cooling system, the enemy is something called "nucleate boiling" which occurs when a localized hot spot develops and allows boiling to occur at that point even if the overall system temp is lower than boiling temperature. Once nucleate boiling begins, there are trapped steam bubbles in the system that quickly work their way through the system, lowering cooling efficiency.

The other problem common to automotive cooling system is boiling that occurs at the water pump. As the impeller of the water pump moves, it creates a low pressure region behind each blade. Water boils at a temperature proportional to the pressure so if the water is close to the boiling point, the lower pressure behind the water pump impellor can be enough to initiate boiling. This is commonly referred to as cavitation but is really boiling at a lower than system overall temperature. The end result is the same, a sudden reduction in coolant flow (since steam is compressible), with a resultant increase in engine temp. the primary purpose of a thermostat is to speed up the heating in cool starts - until about 145 your pistons aren't truly round - they are wider across the wrist pins to to make up for the different expansion rate of the wrist pin (steel) and the skirt (aluminum - and other parts as well haven't taken their at temp shape or clearances - check into "hot Boring" - there is a reason most high end shops now heat the block before the bore - thesize can change as much as .001 from 80 - 180 degrees!) and oil flow is sluggish - running cold is as or more damaging than running hot - no thermostat means you are subjecting your engine to cold wear for a longer period of time!

The secondary purpose of a thermostat and/or a fixed restrictor, is to allow the water pump to build pressure in the block. With increasing pressure, the boiling point of the water in the block increases. This is the real effect of the restrictor, it has nothing at all to do with "slowing the water down" or "keeping the water in the radiator longer". The equations covering heat transfer to air (from the radiator) are independent of the fluid flow but very dependent on air flow. And finally it's important to understand that without a thermostat or restrictor you can be at 170 in one spot of the head and 230 at another! this is NOT conducive to long life of the core as warpage and cracking is much more likely. Compound thermostats not only close down when cold - they open at temp and close slightly at over temp - to reduce nucleate boiling!
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H
jwmbishop said:
Not true. Simply not true.

In a typical automotive cooling system, the enemy is something called "nucleate boiling" which occurs when a localized hot spot develops and allows boiling to occur at that point even if the overall system temp is lower than boiling temperature. Once nucleate boiling begins, there are trapped steam bubbles in the system that quickly work their way through the system, lowering cooling efficiency.

The other problem common to automotive cooling system is boiling that occurs at the water pump. As the impeller of the water pump moves, it creates a low pressure region behind each blade. Water boils at a temperature proportional to the pressure so if the water is close to the boiling point, the lower pressure behind the water pump impellor can be enough to initiate boiling. This is commonly referred to as cavitation but is really boiling at a lower than system overall temperature. The end result is the same, a sudden reduction in coolant flow (since steam is compressible), with a resultant increase in engine temp. the primary purpose of a thermostat is to speed up the heating in cool starts - until about 145 your pistons aren't truly round - they are wider across the wrist pins to to make up for the different expansion rate of the wrist pin (steel) and the skirt (aluminum - and other parts as well haven't taken their at temp shape or clearances - check into "hot Boring" - there is a reason most high end shops now heat the block before the bore - thesize can change as much as .001 from 80 - 180 degrees!) and oil flow is sluggish - running cold is as or more damaging than running hot - no thermostat means you are subjecting your engine to cold wear for a longer period of time!

The secondary purpose of a thermostat and/or a fixed restrictor, is to allow the water pump to build pressure in the block. With increasing pressure, the boiling point of the water in the block increases. This is the real effect of the restrictor, it has nothing at all to do with "slowing the water down" or "keeping the water in the radiator longer". The equations covering heat transfer to air (from the radiator) are independent of the fluid flow but very dependent on air flow. And finally it's important to understand that without a thermostat or restrictor you can be at 170 in one spot of the head and 230 at another! this is NOT conducive to long life of the core as warpage and cracking is much more likely. Compound thermostats not only close down when cold - they open at temp and close slightly at over temp - to reduce nucleate boiling!
Click to expand...
If you have a uprite radiator i might say well sounds good but reality is any real race car has a block has a water pump heads all of that are engine is 650 hp none of us use a thermostat or restrictor we don't get rid of our engines after every race we rebuild them after 1000 laps none of that which you claim happens to any of our motors its all about water velocity http://www.stewartcomponents.com/tech_tips/Tech_Tips_3.htm
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shoeboxlen
check you timing maybe its too far advanced. i had the same issue and mine turned otu to be timing.
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jwmbishop
High Roller,
I'm confused.
the link actually COMPLEMENTS - not refutes, what I posted? yet you say "sounds good BUT reality" ....

I started my post with "typical automotive" not "racing aplication"...

And are you sure that no racers run either? How sure of that?

Last I checked failure to use a therm voids warranties on ECR, TRD, Honda, GM Goodwrench and most other racing engines. Mine included (although I did retire from engine building 15 years ago).

John Wm Bishop
Bachelor of Sciences , Deans List
Automotive Design Engineering
San Jose State University

http://caltechbook.library.caltech.edu/1/ is where you can locate the book from which I used the principals quoted. Sorry for the edits - bad spelling day from too much beer last night.
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jwmbishop
shoeboxlen said:
check you timing maybe its too far advanced. i had the same issue and mine turned otu to be timing.
Click to expand...
Good point - especially if vacc adv is connected!
And last night it occured to me - age of water pump - two years can erode the impellors IF you grounding triangle (batt to block, block to frame and frame to batt) is not suffiecient - five years even if it is. erroded impellors would do the same thing - good volume at low RPM - but at high RPM it would just beat the water up instead of giving needed volume - at least on a chevy its easy to ceck, pull pump, pull plate and look! the impellors are quite visable compared to other makes.
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H
jwmbishop said:
High Roller,
I'm confused.
the link actually COMPLEMENTS - not refutes, what I posted? yet you say "sounds good BUT reality" ....

I started my post with "typical automotive" not "racing aplication"...

And are you sure that no racers run either? How sure of that?

Last I checked failure to use a therm voids warranties on ECR, TRD, Honda, GM Goodwrench and most other racing engines. Mine included (although I did retire from engine building 15 years ago).

John Wm Bishop
Bachelor of Sciences , Deans List
Automotive Design Engineering
San Jose State University

http://caltechbook.library.caltech.edu/1/ is where you can locate the book from which I used the principals quoted. Sorry for the edits - bad spelling day from too much beer last night.
Click to expand...
A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.
This is whats in the link you can read it anyway you want, ok i miss read your "typical automotive" part. Water velocity is now the norm for serious race car cooling No restrictor, computor controlled street cars need a t/sat other then that your going to get more heat rejection with water velocity and a crossflow radiator You don't think Jimmy Johnson at Dover today or anyone else out there was running a t/sat? to avoid N boiling? i personnely no they didn't have one.
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joeelutz
Low (retarded) timing and/or lean can cause that.
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4beers4me
New wire in the radiator hose = no high heat on highway then instant cool down when pulling over. I actually bought a new hose, then realized the radiator side was just slightly too small. So I used the wire out of it in the old hose.

I am getting a lot of coolant pushed out of the radiator even though the temperature never reads hot. Drilled a 1/16" hole in my thermostat (also put it in a pot of boiling water to make sure it was opening). I am using a prestone antifreeze bottle as an overflow :). I plan on replacing that soon, but still concerned with it pushing at least 1/4 to 1/2 gallon out with about 70 highway miles of driving into the bottle.

Answers to questions: new radiator, new water pump, new thermostat installed per manufacturer's instructions, several adjustments on timing.

I now agree, the issue is probably not due to lean conditions.
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acardon
4beers4me said:
high heat on highway then instant cool down when pulling over.
Click to expand...
Tim, are the core support filler panels in place and the hood baffle installed? It sounds like the fans and cooling system is good but not enough air flow at high speed. Does it cool down if you let off the gas and coast at speed or does the car have to slow before it cools down? It could be turbalance restricting the air flow through the radiator from under the hood.
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4beers4me
acardon said:
Tim, are the core support filler panels in place and the hood baffle installed? It sounds like the fans and cooling system is good but not enough air flow at high speed. Does it cool down if you let off the gas and coast at speed or does the car have to slow before it cools down? It could be turbalance restricting the air flow through the radiator from under the hood.
Click to expand...
Yes, they are all in place. The high heat at highway speeds is not an issue any longer. Now I just have to keep radiator fluid in. Which I think may be from the radiator cap. I think radiator fluid goes out, then doesn't get pulled back in. Right now, I think air is being pulled back in and if the radiator heats up, pushes out fluid, cools and pulls in air, then heats and pushes out fluid---after a few cycles the radiator is low on fluid. I am working a 5 liter overflow tank, but first I have to drink all of the beer out of it.:party0031:
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