dtamustang

i'm looking for information on radiator temperature drop from top hose to bottom hose, in other words temp of water going in vs water going out. just guessing i assume it should be 20 to 25 degrees. what i have now is 11 at idle and 6 at cruise speed i just can't believe that is correct. all is well until i have to sit at a traffic light for 3 or 4 minutes, electric fan comes on,temp continues to slowly creep up, once moving again fan stays on for a long long time before temps start to slowly come back down. its not a critical thing now but as south fla temps go up it soon will be.temp now stays around 185 until stuck in traffic
thanks,don


any hard info would be much appreciated

72 convertable
502
4 spd
A/C

7T1vette

Is your thermostat opening properly? Also, what temp stat is it? In warm areas, you'd do better to install a 180 degree stat (if not one already). Take it out and put it in a pan of boiling water...see if it opens completely. Other possibilities are flow blockage in the radiator and/or water pump problems.

SIXFOOTER

Before going all thru that stuff, the t-stat is working (opening) or you wouldn't get any hot water at all in the radiator. Make sure you are pulling plenty of air thru the radiator with the fans on. Are you running a shroud? How well do the fans fit? Is the radiator clear (leaves and crap on the front)
What radiator are you running? Fans?
If stock type rad, is it clean inside? Did you flush it when you installed the fans?
I don't know what the temp drop across the rad should be, I would guess your asumption is about right, so the issue has to be thermal transfer, either water flow or air flow.

7T1vette

Kinda what I already said.... poor water flow or restriction in the system--which still could be a partially opening T-stat. {I don't recall saying that I thought it was totally closed.}

dtamustang

t stat is opening @ 160, flex a lite puller, fits pretty good 1/2" short on the sides top and bottom dead on.shroud is the soft foam that comes with the fan. had the same problem wit the stock fan, i assumed it was the missig seals ect on the shroud that was the cause. A/C condensor installed the same time as new fan , virtually nothing changed. also has new aluminum rd ( not sure of the brand) . the fan is definetly pulling a lot of air ( hot air).
i'm kinda stumped , would a wrong rotation water pump do something like this ? i'm running out of things to try.
thanks for the replys
don

dtamustang

i'll add a little bit of info, the reason i have this car at all is, a friend of mine put a crate 502 in and could never get it to run right, performance was a major problem along with this cooling thing. new water pump, rad,msd distrib, you name it he changed it. he just threw in the towel on it after 2 1/2 years of beating his head aganst the wall. i have the performance up to snuff , thanks to LARS info on timing and quadrajets. ( this thing is a beast)

gingerbreadman1977

i agree with what you said 7t1vet. what you said was great first up checks and kind of just got repeated . i wouldnt have said quote" going through all that stuff " after going through all the stuff that sixfooter and 7t1 said and it fails put your hand in front of you ac condensor ..your fans should be powerfull enough that you feel the air being sucked in through the front. also you running a 502. that requires a radiator that is sufficient for that motor. you say its an alloy but dont even know what type it is. could be a skinny barely good enough 2 core for something else..i would be looking into that.

ghoastrider1

I agree,its either to small a radiator, poor air flow,or both.Cheapest quick check tho is that thermo.I have seen sludge around a thermo( fairly new) restrict the flow and act like described above. Tough problem you have on your hands.

7T1vette

Another possibility {strangely enough} is that you have a too much water pump on the car. The pump, radiator, etc. all have to be well matched to get the most efficiency out of any cooling system. If a high-flow water pump is matched with a "standard" performance radiator, you'll pump a lot of water through it....so fast it doesn't have time to cool! It would be a little odd for that to happen--but you know what components you have. Check with the pump manufacturer to see if the other components are well matched for it.

SIXFOOTER

7t1, NOT BAGGING ON YOU AT ALL
Look at it this way tho, If the T-Stat was only partially opening or hanging up or whatever, and that was all that was wrong, you would have a very high temp differential across the radiator dur to the slow flow rate in an otherwise healthy syetem.
With the further info by the OP I am leaning with Ghost and Gingerbread, the radiator may not be all it should be.
Do a little research on the rad, see what it is. Dewits and some of the others have 2 rows of 1" tubing, if it has less than that with that motor its to small.

and your right, if there is a high flow pump on there IT could cause the problem

dtamustang

thanks for the input guys,i have thermocouples in both ends of the top hose and at the rad end of bottom hose,tstat is opening @ 160.my guess is also that if it wasn't opening all the way my temp drop across the rad would be much higher due to slow flow through the rad. i'll look a little deeper into what exactly the radiator is. my gut feeling is that its NOT an airflow problem,with identical symptoms with both mechanical fan and electric fan,also at 35-40 mph the fan is pretty much out of the picture,and it still takes a long long while to finally see the temp start back down, to me at least that kind of rules out airflow.there is an edelbrock hi flo pump on it, and at least by looking this rad is huge and thick,i'll get some measurements after work today. i'm leaning the direction 71vette mentioned TOO MUCH water flow, that would explain less of a temp drop as rpms go up,it would also explain why it takes so long to cool off at cruise.
again thanks for the input,its all very much appreciated,
don

gingerbreadman1977

excellent. u might find that bubba even discarded the thermostat in there some time ago.

427Hotrod

If it was a complete ZZ502..they usually came with reverse flow pumps for a serpentine system. Might check some part numbers.

My 540 uses a stock 4 row radiator with a fixed flex fan, stock pulleys and that keeps it cool even in TX temps. On long 100+mph runs it would creep higher..but not overheat. I run without a T-stat most of the time these days. Eliminated that issue and the engine temp gets up Ok as long as it isn't too cool outside. Otherwise it stays too low...but if it's that cold I likely ain't out riding around in it with the top down!


Check the pump to be sure.


JIM

SLVRSHRK

Obviously not relevant at idle, but just to make sure we've covered all of the air flow issues.... Does the car have the correct front air dam installed for a big block, or one at all? That will make a difference at highway speeds, ensuring maximum air shoved up in front of the radiator.

69427

Just a couple of thoughts here, and I invite Tom DeWitt to correct me if I am offering any incorrect information here.
There seems to be a lot of concern about water pumping speed and temperature drop across the radiator. My opinion is that the main function of the radiator is to remove the exact same amount of (excess) BTUs that the engine is supplying once the coolant has reached thermostat opening temp (say 180*). The radiator/engine should not care, (within reason) whether there is slightly faster or slightly slower flow through the radiator. At slow flows, there will be a long time for the radiator to cool a small volume of water, resulting in a large temperature delta (drop) across the radiator. At higher flows there will be a shorter time to cool a large volume of water, resulting in a smaller temperature drop. As long as the product of the two functions (water volume and temperature drop) is equal, it shouldn't matter a bunch what the water speed is. The same amount of heat (BTUs) is being transferred out of the coolant to the airstream.
There are secondary issues to think about, obviously. A higher water flow speed will help scrub steam pockets out of the heads, but will also consume more power out of the engine to deliver this extra flow rate, as there is no free lunch here. I also don't know what speed it takes to cause cavitation inefficiency issues, either. A very slow pump speed will yield some reduction in horsepower loss to turn the pump, but while a high temperature drop across the radiator will be seen, there is also the possibility of having a similar (but opposite) temperature delta in the engine, where "very cool" water enters one part of the engine and very hot water leaves it. That situation doesn't seem wise either.
These are just my thoughts. I invite Tom to add his thoughts, or to correct any misstatements I may have made.

greg454

excellent post. I also have installed thermocouples in my upper/lower radiator hoses and found that on average I only see about a 8* drop accross the rad. But that also means there is only a 8* temp rise through the engine.

7T1vette

Not true. Part of the equation determining heat rejection is the time available for the heat to transfer. If the radiator is larger than standard....and it is NOT limed up inside, you shouldn't have a problem. BUT...you can't ignore the possibility that there might be a distinct mismatch with the pump and radiator.

7T1vette

Think of it this way... The radiator has the ability to reject X-amount of heat [given certain operating conditions]; if the amount of heat presented to it is MORE than it can reject under those circumstances, the temp in the radiator (and engine) will rise. It is also true that a hi-flow pump will generate more heat just because of the additional [and unnecessary] amount of work it is doing to pump that water faster.

LiveandLetDrive

Sorry 7T1vette, that is not correct. Faster water flow will always cool better unless you are creating poor flow in the block (eddies) which could create hot pockets. If you are flowing faster the radiator has less time to cool but the block has less time to heat it also. Flowing faster cools better because you have less temperature drop across the radiator and so the temperature difference between the air and the water is higher across the whole radiator. Think of it this way: if you flow extremely slowly the water temp approaches the air temp by the time it gets out of the radiator which is inefficient for cooling. I've been involved in radiator testing in a controlled environment showing exactly this.

It's amazingly difficult to find a straight answer on this question. With so many factors involved it's easy to end up with the wrong conclusion and start putting restrictors in your water flow to slow the water through the radiator. I used to do it too! Wish I could share some of the actual data with you guys but that wouldn't bode well for my career!


A low temp drop across the rad says airside deficiency to me.

SIXFOOTER

Hmmm, interesting.
OP, any idea what the fan ratings are that you have?