Finially--new motor started, water pump problem??

[70herald]

Re: Finially--new motor started, water pump proble

Would high revving the engine, while stopped at a long light
or in bumper to bumper traffic, maintain a cooler operating
temperature?-regardless of having a thermostat installed or
not? ie pushing more water while generating more heat from
faster ignition?

thanks as always,

d

Dale, If I recall correctly you still have the standard fan? Is so, then most likely the biggest effect is the increased air flow caused by the high engine speed. That certainly will keep the engine cooler.
The amount of extra heat you generate by revving the engine (with no load) is fairly small, but in return you get a huge amount of cooling.
Yisrael

 

[eschneider]

Re: Finially--new motor started, water pump proble

Heat transfer, Q, is given by:

Q = U * A * LMTD

where U is the overall heat transfer coefficient, A is the heat exchanger (radiator) area, LMTD is the log mean temperature difference between the hot side and the cold side of the heat exchanger. Increasing the water flow rate (or air flow rate) will increase U. There are a number of correlations for U vs flow rate but they generally are a function of the Reynolds number (and the Prandtl number) - which makes them a function of fluid velocity. Higher velocity gives a higher heat transfer coefficient, more heat transfer and a cooler running engine.

The only danger is turning the pump so fast that it cavitates. In that case, the flow of coolant slows and you overheat.

If think about slowing the water almost to a stop you can see that you'll get really cold water coming out of the radiator, but there will be so little heat removed that you'll still overheat (think of the extreme of no flow).

Sorry for the treatise on heat transfer but I think the "slow flow is better" idea is a myth that should be killed.

Bryan

ah, yes - but with the transfer coefficient measured relative relative to blacksmithing iron, temperature measured in british thermal units, and the area of the radiator measured in cubits, the calculation then involves the second law of thermodynamics (as per Smiths, et al) which states: the consumption of warm ale can never be stopped, only slowed down.

It's been a long time since I sat in thermo class. My gut instinct, though, is telling me that overall heat transfer is time-dependent. Dunno about you, but the longer I wait, the colder my soup gets.

Said another way - yes, the rate of heat transfer is certainly dependent on tranfer coefficient and the temperature differential, but the overall heat transfer is also a funtion of time. Flow rate matters, and not because my soup is in a laminar vs. turbulent state.

To regain focus, though - I, too, doubt the water pump flow rate matters in this instance. I humbly submit the possibility that the radiator may have been collecting goobers over the 7 years, and may need to be cleaned?

My sincerest respect and admiration goes to you for your studies and aspirations. I hope my attempts at humour do not offend.

 

[BryanC]

Re: Finially--new motor started, water pump proble

Well, actually I'm a Chemical Engineer but I hope you won't hold that against me. There is no 'time' element in determining the heat transfer coefficient. The viscosity is a factor but if you have a Newtonian fluid (like water or water / glycol mixes) the viscosity does not depend on the velocity. So changing flow only changes the velocity and U always goes up. If you have a non-Newtonian fluid that is shear-thinning (say, mayonnaise) then all bets are off. Although I don't think that's the only reason not to use mayo in your engine.

You can think about Q=U A LMTD this way. Q is fixed. You always have to take out a certain amount of heat. The area of your radiator is fixed. If U goes down then LMTD has to go up. Since LMTD is the difference between the air temp. and the water temp., the water temp has to go up (too bad slowing the flow won't make the air cooler!). So, when you slow the flow, U goes down and the water temp goes up so that you can take out the heat the engine is making. Slow the flow, the engine runs hotter.

Bryan

 

[hondo402000]

Re: Finially--new motor started, water pump proble

I would be more concerned about your run in procedure, I have read some interesting sites that say if you run the engine too long at the initial start up with out loading and unloading the rings they will not seat and you will not get the most power out of the engine, and once you wear the hone off the cylinder walls the rings will never seat properly, do a search on running in a new engine

 

[kcbugeye1275]

Re: Finially--new motor started, water pump proble

1) I have just read 3 pages of tech stuff and have found all this interesting. I've looked at the same prob. with my sons TR 6, it showed on the gauge to be running hot. A cleaned rad. is a good thing, but when we did it, it didn't change anything. Bottom line on Erics car, the temp. units don't all work the same and shooting it with a thermo gauge at the thermo housing proves that. 2)A water pump cavitating the coolant is a problem racers have running extreme revs., I don't see that happening in a street environment. 3)I've installed a newly rebuilt motor and have revisited this old issue once again and have asked the same round of questions at a different angle and have come up with something more to think about. The question of is a 160 degree thermo really a good thing. I've run one for years. The general feeling I've gotten is throw it away and use a 180. The engine is just happier at 180 and above. Now, how hot is to hot? My dad, a retired GM mechanic(from the cast iron block era), says if the rad. doesn't boil over, it probably is OK. What is everyones thoughts on this point.

 

[70herald]

Re: Finially--new motor started, water pump proble

It's been a long time since I sat in thermo class. My gut instinct, though, is telling me that overall heat transfer is time-dependent. Dunno about you, but the longer I wait, the colder my soup gets.

Been a while since I had to put up with that particular form of torture either /bcforum/images/%%GRAEMLIN_URL%%/devilgrin.gif In the mean time I moved on to Semiconductor physics (for an MS), and I am starting to wonder why???

In any case, in the case of a radiator, it is steady state and constant flow (basically) so it is NOT time dependent. Your soup is time dependent and cools down in a basically logarithmic fashion but that is because at some point you stopped putting soup into the bowl (I hope)
With the radiator, there is a continuous flow of hot water in and out , at basically a constant volume and temp so the time component totally drops out of the equation once we reach equilibrium.
Within reason, we want a nice good flow volume. My guess is that old wives tale about slowing down the water flow came about because someone measured the input and output temperatures on the radiator, and discovered that the temp drop is greater if you slow down the flow rate.
However the HEAT transfer rate is (temp drop * volume)so, with a lower temp drop and higher volume it is possible to get a higher thermal transfer rate.

 

[TR3driver]

Re: Finially--new motor started, water pump proble

Flow rate matters, and not because my soup is in a laminar vs. turbulent state.

Flow rate does matter, but only because if the water inside the radiator gets cooler, less heat is transferred. IOW, faster is better (although how much better falls off rapidly).

Another explanation for why cars without thermostats boil over is that the pressure cap is on the pressure side of the radiator. As the flow rate goes up, the pressure drop across the radiator goes up. If it goes up high enough, then either the lower hose collapses (blocking all flow), or the water pump sucks air in past the impellor face seal. Or the pressure cap starts spewing coolant. Any of these will eventually lead to overheating.

This is why most modern cars have the pressure cap on the low side of the radiator.
https://www.stewartcomponents.com/tech_tips/Tech_Tips_3.htm

Welcome to the Forum, Bryan ! Glad to have someone else who doesn't believe our cars violate the laws of physics !

 

[Dave Russell]

Re: Finially--new motor started, water pump proble

I would be more concerned about your run in procedure, I have read some interesting sites that say if you run the engine too long at the initial start up with out loading and unloading the rings they will not seat and you will not get the most power out of the engine, and once you wear the hone off the cylinder walls the rings will never seat properly, do a search on running in a new engine

There are two main objectives of run in.
The first & most important if you have a new cam & lifters, if they are flat tappet, is to get the two properly mated together. The generally accepted procedure is to start the engine immediately, everything ready to go, no stops to fix leaks, retiming, etc. Run the engine at 2,000 to 2,500 rpm for 20 to 30 minutes. The extra splash lube from fast idle is vital to the cam & lifters. If they are scuffed during this first run, they will never recover, & continue to wear. The type of oil used during run in is critical, but is a different subject.

After this initial run, drive the car at varying speeds & loads to get the rings seated if needed. Different ring materials require different cylinder hone patterns & roughness. If everything is correct, the major ring seating will happen in a very short time. A good engine machine shop will know what hone pattern to use with which ring materials.

On a new engine that I recently built, I did a 40 minute fast idle to mate the cam & lifters. The first 20 minutes of this run required supplemental cooling to keep temps down. A garden hose in the radiator filler & a block drain open. After the first 20 minutes the water temp started dropping rather quickly. A sure sign that the rings had seated & no longer blowing combustion heat past the rings & into the cylinder walls. The supplemental cooling was stopped & the engine run for an additional 20 minutes to make sure that the cam & lifters were mated.

A quick hot compression check was done, all cylinders at 190 psi.

The engine was left to cool to room temperature & head bolt, engine bolt torques were verified.

Additional running has been at varying speeds & loads to complete any additional ring seating that might be needed. Additional compression checks, both hot & cold, over the next 700 miles have shown no change. Additional verification that the rings had seated in the first 20 minutes of run in.

If you think about it, race engines hit the track pretty much ready to go. No such thing as prolonged break in. If the rings don't seat quickly, it's not likely that they will seat more later. It's all in the cylinder hone pattern/roughness/ring material equation. With iron rings, no oil is used on the rings during assembly. Only a light smear on the cylinder walls which is mostly wiped down as the piston/ring assemblies are inserted into the cylinders.

There are other ways to do this, I'm only describing the way I've always done it. Obviously, different ring materials require different cylinder prep & possibly different break in. All new flat tappet cams & lifters require the same break in procedures.
D