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602 Overheating


CC57

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We had a car with an overheating problem that was cured with a restrictor. We actually made four different size restrictors for testing. When the car slowed down and the water flow rate slowed down it cooled off immediately. The way it was explained to me was the water was flowing through the radiator too fast and therefore not cooling enough before returning to the engine. When restricted too much the water was held in the engine too long and the radiator could not cool the water enough before returning to the engine. Once we had the proper size restrictor we never had another overheating problem.

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I may end up being proven wrong, but I don't believe my issue will be resoved with the addition of a restrictor.

 

For one, it was runing hot when it had a restrictor in it. It's now running hot without one.

 

Next, directly from the Stewart site:

 

"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."

 

 

Next, I purchased a CO tester, ran the test, and the testor did not indicate that I have a leak.

 

So that's both a good thing, and a bad thing.

 

Will keep looking. Maybe check the "timing chain off a tooth", "battery test", ......

 

Heck, may just pull the engine and send it in for freshening. The way I was gettting pushed down the straights when the green dropped (thanks guys, it was fun. Seriously, I was laughing all the way down the front stretch) the engine must be getting tired. ~26 races.

 

And please keep offering advice.

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Another duh moment. Never asked where you are sampling temp at. You can be at 200 in the cylinder head between the intakes - and that's perfect.

 

At the intake manifold next to the water neck.

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I had a similar problem with my modified a few years back.New engine,new Afco raidiator,hi performance waterpump etc.Could not find the problem.Finally frustrated I cut off the tank on the inlet side of the raidiator and WALLA scale had plugged 3/4 of the tubes.The engine block and heads were hot tanked but scale was still there.I finally added a Gano inline water filter in the top hose and was surprised how much scale filled the filter.It took about 8 races before it finally cleared up.Now I install a filter every time I rebuild an engine or one gets hot.My truck blew a raidiator ( common for Fords ) so I installed a filter with the new raidiator.It plugged up the first trip to the track.That engine has over 300k on a 7.3 and has had antifreeze all the time I owned it.Still,boiling the coolant broke loose some kind of scale,plugged the Gano filter and ran hot.After it cleared up,the truck runs cool even th the heat of the day pulling my trailer with the a/c at 70 mph.

 

So a partially plugged raidiator can cause your problem.Looking at the flow while runnung cant show anything eather.My race car flowed like crazy.But only the top few rows.

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with the years I helped robert I learned tht if ur timming is too high the motor will run hit. I've even seen ppl change the jets too help with the temp. an the last thing you my check is the radiator fill above the thermostat housing if not it can cause air pockets causing overheating an check ur lower radiator hose an make sure it still has the metal wire in it if not it will suck in causing over heating. forgot one thing u may need too omput ur elect fan between the nose pice an radiator where it pushes the air an not pulling it.

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First off 1-crew - the restriction raises the pressure all the way to the low pressure point at the impellor. As this point can be well below the system pressure (especially if sucking the lower flat or the radiator is plugged) it's boiling point there is the lowest point in the entire system. Once it makes bubbles at the impellor (this is what starts cavitation) - those bubbles then nuclaete at the block walls, cyl head etc where heat is being added. By increasing pump head pressure mechanically you are increasing the low side as well - thus raising that boiling point. This is what the ford flathead v8 taught the engineers. It would take an hour going thru the desert to hit 180, the next 20 minutes it would shoot up. Raising the radiator pressure still left the pump low side below atmosheric and starting to boil there. Remember if you heat water to 218 at 3000 ft it won't boil - lower it to sea level it will - even without applying any more heat because it is already above the boiling point!

 

Now overall regarding water speed etc. Changing fan cfm, water speed etc are bandaids to engineering the system. Slowing the pump also reduces the cavitation by lowering the turbulence effect.

 

Think of the engine and cooling system as a "system" in a black box. The more heat you remove from that "black box" the lower the temperature of the entire system is going to be.

 

Let's ignore the thermostat for now since it only controls the lowest engine operating temperature. Let's say you have an engine that is running at equilibrium (steady state) at 200 degrees at the outlet where you're measuring the water entering the radiator at 200F. Let's say your fan, radiator, etc. is able to remove enough heat to drop the exit temperature to 160F. So the average temperature across the radiator is 180F. The engine is running hotter than you want it to.

 

Look at the convective heat transfer equation:

 

Q = hA(t2-t1)

 

where Q is the amount of energy (heat) removed, H is the convective heat transfer coefficient (related to airflow, turbulence, etc.), A is the surface area of heat transfer (radiator size), t2 is the AVERAGE radiator surface temperature, and t1 is the air temperature.

 

To lower the system temperature, you need to remove more heat from the system.

 

Now let's say you have a water pump that you can increase the coolant flowrate with. As you increase the flowrate, the temperature of the radiator outlet goes up because it has less time to cool. HOWEVER, YOU ARE REJECTING MORE HEAT from the overall system because the temperature difference is larger between the air and radiator.

 

This will continue to decrease the temperature of the entire SYSTEM, until equilibrium is again reached. That equilibrium will be at a lower temperature than with the lower flowrate, because you're removing more heat from the system at the higher flow rate. If you remove more heat, you reduce the temperature of the system.

 

It's a little hard to explain in a transient situation, but I hope that helps.

 

Another useful equation to help understand heat transfer relates to mass flowrate and specific heat of the fluid:

 

Q = mCp(t2-t1)

 

where Q is heat removed, m is the mass flowrate, Cp is specific heat of the fluid, and the temperatures are the fluid and surface temperature.

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I would say with all you checked and after you do a leak down, pull the timing cover and see if its not off one tooth...We had a super stock a couple of years back...After we freshened it up,it would do just as you said yours has done..We lined those gears up, and presto, it was fixed.....Frank t

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I would say with all you checked and after you do a leak down, pull the timing cover and see if its not off one tooth...We had a super stock a couple of years back...After we freshened it up,it would do just as you said yours has done..We lined those gears up, and presto, it was fixed.....Frank t

i mentioned that in post 17 ..so i second your ideal ..lol .. thats one over looked problem that rarely happens ....

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Humor me on this.

 

Water speed has little to do with it - heat transfer is a constant speed based on differential of temps between the surfaces. It's the volume of water containing the ability to take heat and the volume of water with heat stored for transfer out. If it's spending more time in the radiator getting cooler - it's also spending more time in the engine getting hotter. It's the same thing that goes thru our mind when we think we can grab something hot but if we do it fast enough we won't get burned.

 

next time you are at temp hit the radiator outlet with the laser thermometer (be sure your dot is at the aluminum just ahead of the hose). If at the water neck you are 240 and at the rad out you are at 140 - your op temp in the middle (equilibrium) is 190. This is perfect. Speeding the water up would raise radiator inlet temp (more volume per minute drawing heat) and lower radiator out temp (more volume of coolant with heat removed) So lets say the out becomes 250 and in becomes 130. Still at equilibrium temp of 190! Still perfect BUT likely to boil off and loose water. So changing restriction does not necessarily make the engine cooler (it has little to no effect on equilibrium temp) - it merely narrows the spread between high and low temps and makes your GUAGE cooler - the closer the guage is to the hottest point the more effect it will see from the change.

 

The best way to measure is either with two temp guages (hottest and coolest points), or locate the sampling where the engine tends to already be at equilibrium. That what the engineers at GM did by putting the sender hole in the head between two intake valves at a point where the cyl heads heat has not been fully introduced to the coolant.. that location typically runs 10% above eq temp.

 

The best cooling would occur when your temp into the radiator is at it's highest point (the larger the difference between ambient air temp and radiator surface temp the more heat to be transferred AND the faster the heat transfer) - as long as it not boiling. It's as easy as the more heat you have available for removal the more heat can be removed! The more heat you make the more power you are making - the more heat you RETAIN the more power you can make!

 

In racing the idea is always to get as close to the edge as possible. 205-215 in the head is NOT bad (as long as you are not detonating or vapor leaning - the higher the comp ratio the lower the temp margin) - yet can see 230-240 into the radiator! You lower that high point temp, your actual equilibrium temp does not change, but your head temp drops to 200 - you just lost power. Once you determine your eq temp - the gauge is merely a reference - it is NOT the standard. If in fact your eq temp is too high - look at the equation - approach the other factors - heat created would be timing and mixture, heat removed would be air flow, surface area and fin count of radiator.

 

One thing about electric fans - they draw air straight thru the radiator - with an engine fan you can change the angle of the radiator so its not parallel to the fan - this forces the air to deflect more and turbulate in the fins, "scrubs" a little more heat that way!

 

I would hate to see you chasing a "cooling problem" if one does not truly exist.

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Humor me on this.

 

Water speed has little to do with it

 

I wish I would have had all your great knowledge and theories years ago. I would not have wasted my time making four different size restrictors and running about 80 laps on pracitice night to solve our overheating problem. I will pass the word on to our engine builder as well. ;) Oh, but wait, the restictor did solve our problem so we did not need all your vast knowledge. I guess the "Water speed has little to do with it" was the little we needed. :lol: Are you humored now? :lol::lol::lol:

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We had a car with an overheating problem that was cured with a restrictor. We actually made four different size restrictors for testing. When the car slowed down and the water flow rate slowed down it cooled off immediately. The way it was explained to me was the water was flowing through the radiator too fast and therefore not cooling enough before returning to the engine. When restricted too much the water was held in the engine too long and the radiator could not cool the water enough before returning to the engine. Once we had the proper size restrictor we never had another overheating problem.

 

Yes we have done this many times and it has worked great

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If the radiator is too small thereby not providing enough surface area for adequate heat transfer wouldn't this cause a steady heat-up even after the system has reached it equilibrium point? I have always simplified the radiator and thought of it as a large Al. heat sink and by that though if the water isn't it in contact with the radiator long enough to transfer all of the heat out of it wouldn't this cause over heating issues? It would seem the equilibrium idea relies on the same surface area putting heat into the water and taking it out and I would imagine that’s not true? If the surface areas are different there must be an optimum amount of time the water would spend in both systems to promote optimum heat transfer?

 

I dropped out to run my business just before my first symester of thermo-dynamics so I could indeed be wrong?

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I just love discussion in the Grease Monkey Hangout section.

 

I know it's easy to get offended, but the exchange of ideas is very, very helpful to many teams who are going through learning curves.

 

Nick

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Hi Tech, just saw your post...After it happened on our car, others told me that they had seen this before...I would also put much faith in Greg Spreens comment on the restrictor, That man is SMART....Frank t

so it happens more than i thought .untill this thread i have not thought aboult this problem for over 20 years .. with the four bangers and just alittle cam timeing they never get hot becuz of it ..the motors we run anyway .. .....i can see it happen more with v8s cuz of cam adjustment they are able to do .......

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The restrictor changes flow rate (volume over time) which can effect (equally) both sides of the thermal transfer equations. Speed (distance over time - aka velocity) is not a part of either equation.

 

The restrictor does change the temp at the highest point. I've used restrictors hundreds of time - at first any time a guage showed over 225 - but then as learned only IF the water is actually boiling away or I have seen evidence that the eq temp is too high (uncontrolable detonation etc.). Yes the restrictor will lower the temp at the guage - if the guage is reading any point in the system that is above the eq temp. If the guage is reading at a point BELOW eq temp the same amount of change would be seen in the other direction.

 

No restrictor - 245 guaged engine out 145 in = 195 Eq temp

restrictor 225 out 150 in = 195 eq temp

 

Yes the guage went down 20 degrees. But are you running any cooler? And do you REALLY want to lower eq temp if you are below 200?

 

Stop looking at how much heat is PRESENT - engine outlet temp, and focus on how much is is REMOVED - difference between engine out and radiator out.

 

fsae - yes but thats a RATE (volume over time) function NOT a speed (distance over time) function - and as you can see in both equations below lowering that volume is a band aid - the time is not a stated value of the equation - it is merely a component of the function of h (first equation) and has less effect on Q than A does.

 

If eq temp is in a constant upward state - to increase Q you must have an equal adjustment on the other side - Increase A, make better use of h or avoid high t1.

 

Q = hA(t2-t1)

 

where Q is the amount of energy (heat) removed, H is the convective heat transfer coefficient (related to airflow, turbulence, etc.), A is the surface area of heat transfer (radiator size), t2 is the AVERAGE radiator surface temperature, and t1 is the air temperature.

 

or

 

Reduce horsepower production - timing\afr (Value of Cp), increase m (here is where a restrictor lowered the hottest part but made the system less efficient) or avoid high t1

 

Q = mCp(t2-t1)

 

where Q is heat removed, m is the mass flowrate, Cp is specific heat of the fluid, and the temperatures are the fluid and surface temperature.

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We replaced our faulty temp gauge last week. The truck ran 190 the whole race last night. Guess we got lucky that it was just the gauge. I was pretty certain it was because of the crazy reading we would get on the old gauge that didn't jive with reading I would take with the pyrometer.

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Well, over the weekend:

 

1) Ran CO test on cold and hot engine. Engine passed both

2) Pressure tested and tested good.

3) Placed a temp gauge in a spare port on intake. Compared it against the in-dash gauge. In-dash gauge was slopw to respond, but indicated teps close to the "temp" gauge'. Ordered new gauge today.

4) Picking up a new 28 - 32# radiator cap

 

Will replace the gauge and cap prior to next race and "cross our fingers" ...

 

And then go from there if there's a problem.

 

Without grinding the dang "seal bolts" off of the timing cover, I'm going to hope it's not the "1 tooth off" scenario.

Guess I'll find out either after this season when I pull the motor to freshen.

 

Or when it blows up :(

 

 

Chase, 190? You gottta be kidding me... If you don't mind, I'll stop by y'all's pit next time at HMP.

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...Chase, 190? You gottta be kidding me... If you don't mind, I'll stop by y'all's pit next time at HMP.

No Robert, not kidding. 190 on the track - climbed to just over 200 as he sat in the pits waiting to go through tech.

 

Like Thumper mentioned - we swtiched to an electronic water temp gauge. The old one was mechanical and was clearly not accurate - not even close

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190 on the track - climbed to just over 200 as he sat in the pits waiting to go through tech.

What does it climb to after coming off track and shutting down (swelter)?

If it were my call I'd tape off some entrance air and push it to 205 track, 235 swelter for a test or two.

power is heat, heat is power.

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Like Thumper mentioned - we swtiched to an electronic water temp gauge. The old one was mechanical and was clearly not accurate - not even close

What did y'all install? Where did you purchase it?

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