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m21man

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Discussion starter · #1 ·
hey guys i have a 355sbc with m21 muncie and a 4.10 rear end.

it runs 180-190 all day long in the city and at idle it never gets above 190.

but after 5 minutes on the highway doing 70-80mph (3600-3800rpm) it creeps up to 230 and will go from 220-230 depending on my speed.

i have stock radiator with stock shroud with edelbrock high flow pump and NO thermostat; do you think it's time for an aluminum radiator? would that solve my highway issues?
 
#2 ·
I'm no expert but I have heard somtimes they run cooler with a thermostat because of pressure vs flow.....its a cheap try...Is it a 4 core radiator?....that gear is'nt helping though.
 
#3 ·
What kind of fan are you running? Most flex type fans will flatten out at higher rpm and block air flow. Your symptoms sound like this could be the case...

You really should run a t-stat, if your cooling system is up to snuff it will regulate the coolant temps and keep your engine at a more consistent temp. It will also insure your engine gets up to operating temp quicker...
 
#4 ·
You need to put the thermostat in, im almost willing to bet that will fix it.

What happens is with your higher engine speed the coolant is flowing at a faster rate thru the radiator and not having time to cool down any, but at idle the coolant is circulating slow enough to lower the temp as it passes thru the radiator.
TJ
 
#5 ·
If is not the fan or shroud..on the highway there is far more air than any fan can supply...hell it will run without them fine.
high flow pump and NO thermostat;
Click to expand...
The issue is not so much no thermstat but rather lacking the measured restriction of the thermostat hole... do not get any old 180 from the spares shop, get the std GM speced on or the GM high flow speced for your engine.
Rates of opening , how much opens, the diam of the hole all vary as to the application they are for.
You have classic symtoms of no thermostat.

The other issue could be the bottom hose re enforcing ring inside has corroded and collapsed, which causes the bottom hose to suck in and partly restrict the coolant...good possibilty considering your final ratios.. highway cruise rpms.

The other issue could be the radiator need cleaning...not flushing, but cores manually cleaned..

do you think it's time for an aluminum radiator?
Click to expand...
Nope just routine maintance and set up like the factory intended....
The factory cooling system back then was WAY WAY over built for the application...hence why they run for yrs cores blocked up with no issues...till they get really blocked up.
you can spend a lot of money getting a Al radiator install etc, or get yours serviced at a fraction of the cost...its your money.
 
#6 ·
Is your stock radiator 2 or 3 core? If it's 2 core and hasn't been cleaned out in a while, it could be your problem.

Not to argue with others here, but I ran without a thermostat for many years in my moderately built 355 (11:1 compression with 5.xx gearing) and never ever had a hint of an overheating problem, but it's the cheapest thing to try so I would go for it first. Next I would suggest you might be running lean on your jetting which would show up in the RPM range you are talking perhaps. Next I wouild go after the radiator if you still have problems. Flush it good first (cheap) and if that doesn't work and you end up buying a radiator get an Aluminum one.
 
#9 ·
z28kid said:
You need to put the thermostat in, im almost willing to bet that will fix it.

What happens is with your higher engine speed the coolant is flowing at a faster rate thru the radiator and not having time to cool down any, but at idle the coolant is circulating slow enough to lower the temp as it passes thru the radiator.
TJ
Click to expand...
The device that removes the heat from your engine is a radiator, not a water cooler. You want the radiator to be as hot as you can get it to remove as much heat as possible, which means pumping as much mass through the radiator as possible. Any lowering of the outlet temperature will be accompanied by a raising of the inlet temperature in order to maintain the average radiator temperature required for heat balance.
The same physics applies to the air side, you want to pump as much cool air as possible through the radiator in order to maintain the highest temperature difference between the hot radiator and the cooling air.
 
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#11 ·
onovakind67 said:
The device that removes the heat from your engine is a radiator, not a water cooler. You want the radiator to be as hot as you can get it to remove as much heat as possible, which means pumping as much mass through the radiator as possible. Any lowering of the outlet temperature will be accompanied by a raising of the inlet temperature in order to maintain the average radiator temperature required for heat balance.
The same physics applies to the air side, you want to pump as much cool air as possible through the radiator in order to maintain the highest temperature difference between the hot radiator and the cooling air.
Click to expand...
Without a restriction slowing his coolant the cooling system is just a heat pump, if what your saying were true we wouldnt have any use for big multi core alum. radiators or the nice edelbrock water pumps.
Its plain and simple that without his coolant taking the time to transfer some of the heat when passing thru the radiator the system will not work properly.
TJ
 
#12 ·
OH crap here we go again....never mind lol A thermosta is only a couple bucks he may as give it a go right?

Don't they even make washers that will restrict flow for radiators for this issue also?
Click to expand...
I dont know, but Smokey Yunick did a lot of work on his dynos and on the track didnt run a thermostat, but did run a resticter than was not much different than the flow of a thermostat
And I had issue yrs ago well before internet....and it was not till reading yunick, I tried it...gess what?......I have never had an issue of heating in that time other than 1 water pump died and a few fan belts and hoses.
When the water goe thru too fast it comes out the other side warmer, therefore to pull the same amount of energy out of the motor it has still got to increase the same amount of degrees.

But hey a thermostat is cheap, 10 mins to install..what the hell.?
 
#13 ·
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#14 ·
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The Moroso water outlet restrictor kit allows you to control the coolant flow leaving the engine. This lets you control the amount of heat that is absorbed by the coolant. The kit consists of three plates with 5/8'', 3/4'', and 1'' holes for optimum flow. All have a 2-1/8'' outside diameter and come in red, blue, and gold anodizedaluminu
 
#15 ·
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Mounts under water neck on the intake manifold to restrict water flow for improved heat dissipation and cooling. Includes three plates (5/8'', 3/4'', 1''). Fits GM V8, V6 & SB-Fords.
 
#16 ·
Steptoe said:
When the water goe thru too fast it comes out the other side warmer, therefore to pull the same amount of energy out of the motor it has still got to increase the same amount of degrees.
Click to expand...
Yes, but the number of passes the water makes through the radiator in a given time is higher which more than offsets the increased temperature at the exit in a single pass. Same principles apply to the air side of the radiator, that's why you want air moving through the radiator at the highest speed possible. Higher velocity means higher RE number, boundary layer is smaller and heat transfers better.
 
#17 ·
srode said:
Yes, but the number of passes the water makes through the radiator in a given time is higher which more than offsets the increased temperature at the exit in a single pass. Same principles apply to the air side of the radiator, that's why you want air moving through the radiator at the highest speed possible. Higher velocity means higher RE number, boundary layer is smaller and heat transfers better.
Click to expand...
The air is what is doing the cooling, so you do want it going thru at the highest rate possible. But, the coolant needs to be going thru slower so it can transfer its heat before being pumped back into the engine.
You run the risk of cavitation, detonation, and oil failure without a thermostat.
TJ
 
#18 ·
z28kid said:
The air is what is doing the cooling, so you do want it going thru at the highest rate possible. But, the coolant needs to be going thru slower so it can transfer its heat before being pumped back into the engine.
You run the risk of cavitation, detonation, and oil failure without a thermostat.
TJ
Click to expand...
What really "does" the cooling is the difference in temperature between the radiator and the air you put through it. The closer the radiator comes to the air temperature, the less heat is exchanged. This is why you want the radiator to be as hot as you can get it if you are experiencing cooling problems, the same as you would want the air as cold as you can get it.
If you were to divide the radiator core into three equal sections, the inlet, the middle and the outlet, would you want the highest heat exchange efficiency from each section? You won't get this by slowing the mass flow through the radiator, you will get this by maximizing the mass flow through the radiator, on both the water and air sides.

Have you ever wondered why a thermostat opens at high temperature and closes at low temperature? It opens at high temperatures to increase the flow of water through the radiator, which heats up the radiator and promotes a higher rate of heat exchange.

If the engine cools down, the thermostat will move towards the closed position, restricting the flow through the radiator, reducing the rate of heat exchange and maintaining the heat balance in the system.
 
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#19 ·
So what are some of your suggestions for solving his overheating problem onovakind67?

m21man, you should just humor me by getting a thermostat and putting in and see what happens... it will only cost a couple bucks and its certainly easier than installing a alum. radiator.
TJ
 
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m21man
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