radiator cap in upper radiator hose?

[5-90]

You guys are such nerds lol. 5-90 I'm still getting used to your new avitar. Just making sure, you want the car to run at it's maximum temperature, within it's limits correct? I see all the time people putting in these different thermostats and huge fans and hood vents on a daily driver with a fine system. I would think that much cooling would keep the motor TOO cool, and perhaps hinder performance?

Not so much that, as that the engine is designed to run at a certain temperature. For later vehicles, the control system knows this (particularly OBD-II,) and it will start yammering if it runs too cold or too hot for too long.

I just happen to not like the fact that AMC designed the thing to run 210-215*, and decided to do something about it. Since RENIX isn't picky, I've managed to pull it down twenty degrees - with no harmful effects on fuel mileage or emissions.

I know that an awful lot of manufacturers are pushing spec temps up, but I don't like it. So, I'll stick to older vehicles that I can play about with, and do what I feel is right and know works.

Whassamatter - you don't like Dust Puppy? www.userfriendly.org

 

[vjarman]

well as of right now my temp gets just above 210 then drops down under when the t-stat opens. thank you everyone for the help. goin to play at the river now to see how it does. thermostat made the difference and getting all the air out of the system.:yelclap:

 

[heavyequipment]

"I remember reading somewhere (probably on this site) that the thermostat acts as a metering device that only allows a certain amount of coolant thru the radiator so it has time to cool down. Without the thermostat, coolant flows thru the radiator too fast and doesn't have time to cool down."

>>Wrong. Doesn't matter how fast the coolant goes, as long as it gets to the radiator before it turns to steam.

 

[vjarman]

well it was either the thermostat that did it or getting ALL the air out of the sytem. before the t-stat was in it as soon as i tried to run it with the cap off the water just shot out of the cap so i couldnt get all the air out. now with the t-stat it wont gush out so all the bubbles come out.

 

[stewie]

The Thermo text also discusses proper flow rate selection. Too low a flow rate underutilizes the heat exchanger surfaces. Too a high flow rate causes cavitation in either the pump or the radiator. Pump cavitation damages the pump and if the coolant is near its boiling point it can cause localized hot spots or steam pockets. If you increase the flow rate to the point of causing turbulence or cavitation in the radiator itself, its efficiency starts dropping very quickly. I think that is more likely the cause of the problem. I also noted a number of engine builders saying they use restrictors to avoid cavitation at high engine speeds.

Of course, an engine is hardly an ideal heat exchanger and local coolant temps matter quite a bit. Especially when the coolant is operating fairly closely to it boiling point.

But thats just me being anal and academic about things. I don't doubt that too high of a flow rate causes problems, but I'm thinking its cavitation thats the underlying issue and not just the flow rate all by itself.

last month when i was in school for my apprenticeship, we learned that certain cavitation of turbulence in a heat exchanger actually helps aid in the heat transfer. there are a number of factors but these are the ones i remember off the top of my head...

the fluid flowing though the heat exchanger (read radiator, variable air valve, condenser, chiller etc) flows at different rates. the fluid on the edges of the line is in contact with the line itself- the tube, pipe, core, etc- and thus has some drag. the fluid more toward the center of the line flows slightly faster with less drag. that means that the fluid on the edges has more time to transfer heat than does the fluid in the center. many heat exchanging devices use an process similar to rifling in a gun barrel to slightly churn the fluid so that more of the fluid actually touches the edge of the line, slows down with drag, and transfers heat more efficiently and evenly.

does the radiators most common in the automotive world do this, no. but some of the higher end heat transfer systems do. i know it doesnt matter to most of us in our everyday lives but its just a little snippet of information

 

[lawsoncl]

Yes turbulence reduces the thickness of the boundary layer and improves the heat transfer. Excessive cavitation however can put a layer of steam between the fluid and the metal, and steam doesn't conduct nearly as well.

For a prop or pump, turbulence is a bad thing. Non-laminar flow or getting streams of cavitation near the blades significantly reduces its ability to pump or push the vehicle.

 

[stewie]

Yes turbulence reduces the thickness of the boundary layer and improves the heat transfer. Excessive cavitation however can put a layer of steam between the fluid and the metal, and steam doesn't conduct nearly as well.

For a prop or pump, turbulence is a bad thing. Non-laminar flow or getting streams of cavitation near the blades significantly reduces its ability to pump or push the vehicle.

true. and excessive cavitation or turbulence can also erode the pipe, line, or fitting. it is a required process to ream the ends of pipe on most systems particularly on copper. its said that if the burr is left on the end of the pipe it will cause a turbulent area that will eventually eat through the tube as well as hampering the flow of fluid though that line. and when a pump hits a "void" caused by turbulence the impeller blades cut though the void and then slam back into the fluid causing excessive stress.

 

[vjarman]

ok everyone change of plans...its still overheating...:tears: i got a new t-stat, new water pump, good hoses, good mechanical fan, good electric fan, all the air as far as i could tell was out of the system. and i am all out of ideas.:wierd:. i dunno if its just cause i dont have the expansion tank or do you guys think its something else? thanks everyone!!!

 

[RichP]

ok everyone change of plans...its still overheating...:tears: i got a new t-stat, new water pump, good hoses, good mechanical fan, good electric fan, all the air as far as i could tell was out of the system. and i am all out of ideas.:wierd:. i dunno if its just cause i dont have the expansion tank or do you guys think its something else? thanks everyone!!!

Well, if it heats up and pushes coolant out of the system onto the road it's going to suck air back in, the overflow tank stops that by putting coolant on top of the hose from the radiator or in your case probably the fitting with the cap he put on there but thats just a guess. What he did was a half way conversion from a closed to an open system with out expansion provisions or coolant recovery.
The correct conversion is a new open system rad with it's own cap and an expansion tank. The adapter would work too but you still need a way to recover the coolant as it expands.

 

[vjarman]

ok RichP, now if i just install an overflow tank from another car and hook a hose to it, do you think that will help keep it cool? or do i have to get a replacement radiator thats the 'open?' style system? thanks again.

 

[stewie]

ok RichP, now if i just install an overflow tank from another car and hook a hose to it, do you think that will help keep it cool? or do i have to get a replacement radiator thats the 'open?' style system? thanks again.

:gee::twak: naw, are you really that dense? of course it will help! your missing part of your cooling system and you cant figure out why your overheating?!?

how about you put down the xj and go back to hondas...

 

[sjkimmel99]

ok RichP, now if i just install an overflow tank from another car and hook a hose to it, do you think that will help keep it cool? or do i have to get a replacement radiator thats the 'open?' style system? thanks again.

If you have a radiator cap designed to work with an overflow bottle as soon as you get the engine hot enough for the cap to let coolant out you're going to loose coolant and suck air back in. What installing the overflow will do is keep your coolant in the engine. Assuming having coolant in the system improves engine cooling capability then yes, it will help.

Also, fwiw, I had one of the upper hose in-line radiator filler adapters. Thought it would be easier to fill from the highest part of the system. Unfortunately it never did make a good seal with the radiator cap and would not draw coolant back into the rad. I removed it and just filled from the regular radiator fill (being a 96 and an open system anyway.) Takes a few days for the level in the overflow to stabilize as air is purged from the system. The in-line unit I had was machined from a piece of aluminum and the two in-line pipe sections actually screwed into the central neck piece and which used o-rings to seal.

Not saying the one you have will behave that way, there are different brands on the market, just something to monitor.

 

[RichP]

ok RichP, now if i just install an overflow tank from another car and hook a hose to it, do you think that will help keep it cool? or do i have to get a replacement radiator thats the 'open?' style system? thanks again.

I'm going thru cooling issues now on my 98, not bad but running a few degrees hotter than it's ran in the last 12 years. I'm putting a new rad in this morning once I get my azz moving, I was going to do it yesterday but every time I got outside a thunder boomer would blow through. My 98 has close to 400,000 on the original rad so I think it may be time. We'll see, the fan clutch seems a might free when it's hot too so if the rad does not fix it the fan clutch comes next, a ZJ one this time, next comes the water pump.

 

[Ecomike]

I'm not sure I buy the theory of not enough time to dump heat. There is certainly enough anecdotal evidence of overheating with no thermostat that is corrected by installing a thermostat or restrictor plate though. I wonder what the real mechanism is.

I can certainly see too high of a flow rate causing cavitation or turbulence and hot spots. Plus raising the flow rate would cause the temp drop across the radiator to be smaller (ie the overall temp of the radiator would be higher and rejecting more heat overall). The return water being hotter could skew where the distribution of heat transfer within the engine.

I can also see the lack of a thermostat throwing off the pumping characteristics of the water pump and getting worse flow. But in general a higher flow normally should improve the overall heat transfer. At least on paper for an ideal heat exchanger.

Now for the original poster, if its the original radiator its probably plugged up by now.

I have never seen a cooling system with out a thermostat that overheated only because the thermostat was missing! I have run several vehicles over the years that were overheating, with out a thermostat to either keep them from overheating, or to buy me enough extra travel time to get around with out it overheating. In fact many vehicles today run rich if they are cooler, which is what happens when there is no thermostat. They stay open loop, rich, and don't run as lean as they would with a thermostat.

 

[Ecomike]

You got me curious, so I reviewed my thermo texts on closed loop dual heat exchangers. For an ideal system, raising the flow rate always increases the overall heat transfer. It's not a linear curve, more bell shaped. Changing the flow rate obviously alters the temps of the fluid in different places of the system which may have its own consequences, but the overall heat transfer does goes up. 1 gpm of fluid passing through an exchanger with an inlet-outet temp diff of 20 degrees, is transferring the same amount of heat as 2 gpm with a 10 degree temp drop.

Certainly too low of a flow rate causes problems. If the coolant is back down to ambient temp by the time its halfway through the radiator, then the second half of the radiator isn't doing anything. Increaseing the flow rate will allow better use of the radiator (ie you can increase the flow rate and still have the same temp drop). Coolant spending too much time in the engine may heat up above boiling.

The Thermo text also discusses proper flow rate selection. Too low a flow rate underutilizes the heat exchanger surfaces. Too a high flow rate causes cavitation in either the pump or the radiator. Pump cavitation damages the pump and if the coolant is near its boiling point it can cause localized hot spots or steam pockets. If you increase the flow rate to the point of causing turbulence or cavitation in the radiator itself, its efficiency starts dropping very quickly. I think that is more likely the cause of the problem. I also noted a number of engine builders saying they use restrictors to avoid cavitation at high engine speeds.

Of course, an engine is hardly an ideal heat exchanger and local coolant temps matter quite a bit. Especially when the coolant is operating fairly closely to it boiling point.

But thats just me being anal and academic about things. I don't doubt that too high of a flow rate causes problems, but I'm thinking its cavitation thats the underlying issue and not just the flow rate all by itself.

Great analysis except for one thing. The 1 gpm at 20 F delta T, and 2 gpm at 10 F delta T, ignores heat transfer rates. The higher the delta T, the higher the heat transfer rate, thus the higher the heat rejection (absorption) rate.

That may not be clearly stated, so let me explain further. If the water entering the engine is colder, say 150 F versus 200 F, the 150 F water at a fixed flow rate will absorb more heat, than the 200 F water. Reverse happens for the radiator. If I double the flow rate, the heat transfer increase is not linear. You need to look at the new equilibrium temperatures, and the heat transfer rate at those temperatures. IIRC there is log rate on heat transfer that is something like ln(T1-T2)? It predicts that the heat transfer rate depends on the ln of the temperature difference. The temperature difference is the driving force that moves heat, and the rate of that movement depends on the LN(T1-T2), IIRC?

On another interesting point, the radiator may at times be a sufficient restriction to flow, especially if it is clogging up, used, such that the system cools better with out the thermostat (clogging radiator takes its place?). Something I may have experienced in the past, with out understanding why at the time. In other words in an older system, the thermostat is restricting flow too much for an old radiator.

Today, I discovered that my system, which has several cooling improvements now has hotter coolant exiting the radiator, than before the changes I made, but the system, tested at the thermostat is running cooler than before. The only reasonable explanation I can find is that my 4 year old 2 row alumiunum radiator was restricting flow (I was getting 30-40 F delta across the radiator which had me thinking it was working properly, but it was 4 years old), and my new CSF, 3 row copper/brass radiator has only a 15 F delta T across the radiator at idle. :dunno:

All I can figure is I am getting a lot more flow through the entire system now as my peak thermostat temp is down a good 20 to 30 F, while the new radiator exit temp is up 10 to 20 F!:dunno:

I now have a 15 F delta T between the engine inlet (radiator exit) and engine outlet (radiator inlet), where as it was 30-40 F with the old radiator. Only other change I made was a new AC condenser.

Another important factor is that heat transfer from metal to water (coolant) is much faster than from metal to air. Huge difference in surface areas needed to move the same amount of heat.

 

[lawsoncl]

I was looking at heat carried away by the coolant, which is defined by the flow rate x change in temp. So 1 gpm x 20*F should be equal to 2 gpm x 10*F.

At the water-metal interface inside the engine, the temperature difference is what determines how fast the heat can transfer to the water. The rate of heat transfer is proportional to the temp difference, assuming the same flow rate as different flow rates affect the thickness of the flow boundary layers. Flow rate is a tricky thing as a higher flow rate at the same temperature can also improve the metal-water heat transfer by reducing the thickness of the boundary layer (assuming smooth flow). Too fast and you get turbulent flow which is much harder to predict.

Your numbers are pretty interesting. From your measurements I'd say you're getting a much higher flow rate. I'm not sure how you'd measure the flow rate though.

 

[Ecomike]

I agree. And there in lies the rub, we have no good, easy efficient way to measure our flows. And thus it is easy to make erronious assumptions about flow based on surrogate data like a delta T, which is what initially led me astray in diagnosing my problem and potential solutions.

Also, had I gone to a higher flow rate, higher pressure/capacity pump, it might not have made much difference in my case, but the new radiator made a huge difference. The delta T went in the opposite direction of what I was expecting. I am still shocked to see just a 15 F delta T do all this cooling!

 

[lawsoncl]

Yeah, it does seem counter-intuitive as a large drop across the radiator can mean its working really well or its plugged up and not flowing.

You need one of these. http://www.ftimeters.com/pdfs/application_notes/an69597_automotive_humvee_mag_meter.pdf Of course I'm not sure I'd want something intended for a Hummer on my Jeep. :}