Tony D Posted October 2, 2007 Share Posted October 2, 2007 Yes, the 10mm line is enough to give your pump some place to pump... If the pump deadheads, it gets into a cyclic situation similar to turbocharger surge. If you ever put a water pressure gauge on the block you can see some interesting things develop when you rev the engine cold... for one, you realize when the thermostat will lift! LOL Anyway, a centrifugal pump likes to make flow at all times. The 'internal bypass' is there in case the external lines get corroded, therefore insuring the pump always has a bypass route. As long as you are reasonably responsible with your cooling system maintenance you won't have corrosion plugging issues. I get told I'm crazy when I tell people there is an 'internal bypass' in the block that will do the same thing as the external line! (Someone on this forum said that as well....hmmmmm I ain't sayin!) The damage comes when there is no place for the pump to push the water. Idle may allow that pump to bypass around the tips of the pump vanes. But you start upping the speed, and you basically have the same situation as a turbo at full tip speed and at peak efficiency coming up against a closed throttle valve. It bangs internally, and the reversal of flow causes a radical drop in pressure. The drop in pressure causes steam bubbles to immediately and explosively form...in some cases it can cause bits of metal to blow out of the impeller blades or the volute in the front cover. Cavitation damage. In large industrial engines I have seen this eat through CAST IRON housings!!! Steam formation in the cooling system---even the pump can cause errosion, pockets that look like 'corrosion' but in reality are cavitation signs, and impellers on the pump that wear away to uselessness. The cavitation can start at temperatures as low as 160 degrees if the thing is surging the correct amount and the antifreeze weak. If the pressure goes high enough, the thermostat spring will be forced to lift...but that's an extreme case. Usually if there is proper coolant mix to prevent boiling, the cavitation will not be much of an issue in the pump, but the cavitation and 'surging' can do some stuff to your seal as well. I would think with the higher volume of the Diesel Pump the bypass would be more important to prevent cavitation inside the pump. There were some TSB's in the old days about 'cavitation' in the L-Series engines, and this is aside from the joke one referring to timing of the alternator to the water pump vanes! Link to comment Share on other sites More sharing options...
340ZXTTAZ Posted January 4, 2008 Share Posted January 4, 2008 Bump!!! Any headway guys? Link to comment Share on other sites More sharing options...
clint78z Posted January 4, 2008 Share Posted January 4, 2008 Some great discussion here, just about all info accurate. Thought I would further explain a bit of fluid dynamics. I am going to over simplify some things to make the explaination clearer. Take a 2" pipe a certain length, pump water through it to cool the pipe. The water will flow at a certain velocity say 7 ft/sec, it will cool the pipe down to a certain temperature. The water flows 7ft/sec on the inside, but on the inner layer called the boundry layer the speed might be 0.5ft/sec if the pipe is smooth. A rough pipe will add turbulence to mix the boundry layer with the rest of the water, this will cool the pipe more. Now if you add too much turbulence the pump won't be able to maintain the same velocity. There are many tradeoffs made here, but that doesn't mean good old fashioned testing and documentation can't fix it. Link to comment Share on other sites More sharing options...
TimZ Posted January 5, 2008 Author Share Posted January 5, 2008 I decided to go with the Evans NPG-R and the diesel water pump and see how that works out. I won't know how well it works until spring. My internal bypass is not plugged and I'm using the Stewart thermostat that has some bypass holes drilled it it as well. After re-reading Tony's post above, another thing that occurs to me is that if you have deadheaded the flow with the Thermostat shut, the only way for it to see the water temp "signal" is for it to wait for the heat in the head to creep out to the t-stat housing via convection. Seems like the temperature of the water in the head could get pretty high before the water in the t-stat housing gets hot enough to open the thermostat. Link to comment Share on other sites More sharing options...
Tony D Posted January 6, 2008 Share Posted January 6, 2008 After re-reading Tony's post above, another thing that occurs to me is that if you have deadheaded the flow with the Thermostat shut, the only way for it to see the water temp "signal" is for it to wait for the heat in the head to creep out to the t-stat housing via convection. Seems like the temperature of the water in the head could get pretty high before the water in the t-stat housing gets hot enough to open the thermostat. And this is why I ALWAYS advocate using the external bypass line from the lower thermostat housing back to the lower radiator hose inlet fitting, and not relying on only the internal bypass in the head/block to recirculate the coolant---the thermostat housing is a deadspot if it's not vented. There are people who argue that 'they have done it for years with no problems' but when you realize why it's there, you start having serious reservations about removing it for any reason. Tim hit it straight on the head! Link to comment Share on other sites More sharing options...
TimZ Posted January 6, 2008 Author Share Posted January 6, 2008 Thanks Tony. I've always had the same reservations when you hear people talk about cycling their electric water pumps on and off. If your reference for the temperature switch is in the cylinder head water passage then you might be able to get away with it, but that always seemed like a bad idea, especially if the temp sensor is in the thermostat housing. How much power can that possibly be liberating, anyway? Link to comment Share on other sites More sharing options...
Makenski Posted January 13, 2008 Share Posted January 13, 2008 a neat video of Cavitation... everyone should watch! It's a real media player file format http://modular.mit.edu:8080/ramgen/ifluids/Cavitation.rm Link to comment Share on other sites More sharing options...
Tony D Posted January 14, 2008 Share Posted January 14, 2008 That's a good film. Anybody remember pencils? LOL Seriously, though, I hope those who told me I was wrong about water pump damage from cavitation see this film and pay particular attention to the discussion about 7 and 17 minutes into the playing. That is exactly what happens in high temperatures within the water pump, especially if the pressure cap is somewhat defficient. And that results in not only pumping loss, but errosion of the impeller and casing. Very good film! Thanks for finding that! Cool! Link to comment Share on other sites More sharing options...
Careless Posted January 14, 2008 Share Posted January 14, 2008 a neat video of Cavitation... everyone should watch! It's a real media player file format http://modular.mit.edu:8080/ramgen/ifluids/Cavitation.rm is that available in another format, because i'd love to watch it, but real player is piss. Link to comment Share on other sites More sharing options...
Tony D Posted January 14, 2008 Share Posted January 14, 2008 I downloaded it pretty quickly, the film is 32 minutes long. Think back (if you are old enough) to school when guys in Horn Rimmed Glasses with white short-sleeved shirts sporting the latest in pocket protection and a sliderule lectured you on the way the natural world was! LOL Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted January 14, 2008 Share Posted January 14, 2008 is that available in another format, because i'd love to watch it, but real player is piss. Google Real Media Alternative for a codec. This thread is really cool and informative, but could we possible get some cliff notes for us dummies (like me?). Thanks, Mario Link to comment Share on other sites More sharing options...
zxtman Posted January 15, 2008 Share Posted January 15, 2008 Posted by: MONZTER The first two pictures show the inlet points in the gasket surface. You will notice that there are holes in the head that are blocked off by the HKS steel gasket. These could flow water if the gasket was opened up. In the second picture you will see holes in the head gasket that do not have holes going into the head. This makes me wonder if this was for a reason, or just a manufacturing convenience, so that 1 head gasket design would fit many application of the different years. I wonder if an improvement could be had by opening the gasket up to the holes in the head, and the head up to the gasket. Hmmm. Now here is my question: I am about to install a new steel head gasket (replacing an old steel head gasket) and I realized, as shown in the first picture above, that (2) coolant passages are blocked by the gasket. Did you found out what the reason is, if any? Does the stock Nissan gasket block the same passages? Anyone? Thanks, zxtman Link to comment Share on other sites More sharing options...
ktm Posted May 19, 2008 Share Posted May 19, 2008 Why is this not a sticky?! Link to comment Share on other sites More sharing options...
cygnusx1 Posted May 19, 2008 Share Posted May 19, 2008 It should very well be a sticky but I think someone should go through and summarize it before it's a sticky. I would suggest creating a new thread that summarizes the findings with the theories and pictures and a link back to this original thread. Not that I'm raising my hand or anything. Link to comment Share on other sites More sharing options...
Tony D Posted May 19, 2008 Share Posted May 19, 2008 Why is this not a sticky?! The sticky is in my head...."there were two posts about rear cylinder cooling" LOL Link to comment Share on other sites More sharing options...
bjhines Posted May 19, 2008 Share Posted May 19, 2008 A Question about SBC v-8s.... I have always wondered at the incredibly small size of the bypass hole on the right side of the V-8 SBC waterpump. It is only 1/4" or so. I this enough to allow non-cavitating operation of the Waterpump? Link to comment Share on other sites More sharing options...
blue72 Posted May 19, 2008 Share Posted May 19, 2008 I'm waiting with bated breath on the head gasket question because I am just about to swap heads, and noticed a few holes which are blocked by the gasket on my Fel-Pro as well. I'll have to take some pictures of my own. Link to comment Share on other sites More sharing options...
cygnusx1 Posted May 19, 2008 Share Posted May 19, 2008 Holy moly, I think I solved a mystery by reading this thread. My car tends to run either perfectly normal temp or way too cold. After reading this thread I think I discovered why. When the thermostat is open (hot engine under load), the cooling system is working at keeping the car at a steady temp. When I drive the car with low loads but medium RPMS, the car runs cold. (thermostat checks out fine in a pot of water). Probably because I blocked the old throttle body cooling line which used to double as a bypass. So my waterpump is pushing the thermostat open and overcooling IF my heater valve is also shut. Did I get this correct? Could I have a symptom of improper coolant bypass? Link to comment Share on other sites More sharing options...
X64v Posted May 20, 2008 Share Posted May 20, 2008 So my waterpump is pushing the thermostat open and overcooling IF my heater valve is also shut. I don't quite think so. There is also an internal bypass in the engine block. It's not impossible, but I don't think it's likely. Link to comment Share on other sites More sharing options...
woldson Posted May 20, 2008 Share Posted May 20, 2008 Ok I believe I understand what has been written here enough to ask a question w/a comment. So you guys are trying to inprove effenciancy at removeing heat from the combution chamber esp. in regard to the "hot spots" that create small vapor "pools" in the coolent system. Is this abit (just abit) defeting in the over all function of a turbo engine. Why not get rid of the heat through the exught and help the turbo out as well. (this is with the assumption that this is a good thing) This may or may not be "on topic" but ceramic coatings. Yes, Yes I know this has been covered alot and outside of a few that have had the coating come off, (not settled argument) this allow you to put the heat to good use, increasing effecincey w/o tasking other system in the car. On a side note, I so believe in the coatings that my zx will been coated and meth injection with no intercooler. I do realize that my expertize is not nearly as vast as most of all of you posting, so I hope this might help not hinder. Link to comment Share on other sites More sharing options...
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