brown280z Posted March 6, 2006 Share Posted March 6, 2006 Hello everyone, I am in the process of cleaning up my intake manifold and I was wondering what you guys are doing with the coolant circulation bypass line. I removed the thermal vacuum valve and ideally I want to remove the coolant line that bypasses my thermostat but I am worried about getting hot spots in my engine during warm up. I have searched through previous posts and have seen a few of you guys who just capped off the line and a few of you who warn against it. Has anyone actually cracked a block or caused any damage by removing this line? Thanks for the help! -Mike Car: '77 280z federal Quote Link to comment Share on other sites More sharing options...
briann510 Posted March 6, 2006 Share Posted March 6, 2006 I dont run it at all, never have and never will. I know guys that have had it bypassed for 10 or more years and their engines are fine. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 6, 2006 Share Posted March 6, 2006 How can you argue with anecdotal evidence like that? I'm sure they have cut and sectioned their heads to prove nothing is cavitating. It's there for a reason, if Nissan could have left it off and saved the money for the tubing, clamps, and hose, don't you think they would have? When you look at high-dollar racers that really are making power, they tapped holes in the head and made a manifold log out the intake side of the head so the coolant could cross and exit the head without having to move rear to front and go out only through the thermostat. But guess what? That engine, with all it's mods, still had a -6 Bypass line. I defer to experts, and not anecdotes. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 6, 2006 Share Posted March 6, 2006 I defer to experts, and not anecdotes. Well Rebello built his engine, they should be expert enough to decide if it was necessary... Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 6, 2006 Share Posted March 6, 2006 Did Rebello plug the internal passage on the oil filter side of the block as well? If not, why not? But it's internal, and nobody knows the answer---my bet is the did not plug that internal bypass. The external bypass is a balancing act, because the internal bypass hole is a "dead area" in the head when the thermostat is opened, and it will boil!!! If the thermostat is closed, thethermostat side of the head is a dead spot, and it can boil! Steam is not a good coolant. Incidentally, steam makes a great heat transfer barrier... N/A really isn't that stressful when dealing with cooling systems anyway. Make twice the HP Briann is, and see if the cooling system is still up to par. Like I said earlier, Nissan put how many hundred-thousands of these bypass lines on, all unrequired on a street car---they just wasted their money because they like to use odd-bits of tubing and hose... C'mon, I'm not buying it! If they could've left it off and saved a $$$, they would have, the US Spec 240's didn't have Splash Guards or Fan Shrouds for gawd's sake. You think something that could be deleted worldwide across the entire L-Engine line would have been deleted if it was so unrequired! Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 6, 2006 Share Posted March 6, 2006 You could drill a small hole in the thermostat. As far as Nissan getting everything exactly correct, well I'll have to take issue on that. Remember what site you're on Tony??? Quote Link to comment Share on other sites More sharing options...
briann510 Posted March 6, 2006 Share Posted March 6, 2006 FYI: Rebello told me not to run the bypass just like he tells all of his customers who have his engines its not needed. Its his motor and warranty so I listen to him since hes been building these engines for 30+ years and probably knows what hes talking about. I even asked 4 of his workers that drive and race Datsuns what they did, and they all said they dont run it either. Its not in the norm not to run a bypass thats for sure, but different strokes as they say... "Make twice the HP Briann is, and see if the cooling system is still up to par" well im not making twice the hp I am so what your implying is the bypass isnt needed for low hp engines?? And I dont think the original poster of this thread is making 600+ hp either so does he really need it refering back to your quote? LOL I wonder how many people that dont use the bypass have actually had problems? I bet no one posting on here will say they have. If someone is uncomfortable with not running a bypass dril la hole in the thermostat as suggested. The thermostat I bought at autozone already had a hole in it anyway exactly for this purpose. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 6, 2006 Share Posted March 6, 2006 I never said they got it all right. Chevy has coolant internal recirculation, Ford does, Chrysler, everybody does! And the "small hole" is not the same thing as the internal bypass. The internal bypass casues a quick warmup and gradual heating of the coolant mass, rather than a prolonged warmup that would occur with a 3/8" hole in the theromstat. Every manufacturer used coolant bypass for warmup, and for other reasons. Not one doesn't use it. Yet, here we are again, with someone talking anecdotally about it never causing any problems (that they can see---have they even looked?) I mean, I got to ask why every single manufacturer in the world used that kind of bypass system--at added cost for external plumbing in almost all the cases, when they simply could have deleted it and saved millions of dollars? You have to admit the car companies aren't in the business of leaving beneficial things in cars (oh, like power) unless there is a price increase. What makes anyone think this is any different? Why would they put it there if they could stuff that hose money in their pockets? Nobody has answered that question about the charity of the Big Three and everyone else giving us these little coolant bypass lines all over the place. I have seen firsthand what coolant cavitation does to cylinder liners, and it's not pretty. You can eat through a casting, literally! Steam impingement is a bad foe... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 7, 2006 Share Posted March 7, 2006 FWIW if you do drill a hole, make it more like 1/8". If you go 3/8" the thing will never warm up. I did 1/4" in my pickup and even that takes forever. Quote Link to comment Share on other sites More sharing options...
brown280z Posted March 7, 2006 Author Share Posted March 7, 2006 Thanks for the input on this topic. I do agree that leaving the bypass line is probably the right thing to do for overall engine warming predictability, but this is a project car that will never exceed 200hp (well, probably not)and will never be subjected to extreme environmental conditions. I guess I was just wondering if anyone has heard of or personally experienced a damaging effect by removing the bypass and just capping the ends. Mike Quote Link to comment Share on other sites More sharing options...
zane9000 Posted March 7, 2006 Share Posted March 7, 2006 Just to stirr the pot a bit. On my old enigine I didnt have a bypass line. I had LOTS of issues with over heating, then my engine blew up in a few different ways. Then again I also have an "anti-lion rock" sitting outside my house and I have not once had a lion attack my residence! -Warren Quote Link to comment Share on other sites More sharing options...
zguy36 Posted March 7, 2006 Share Posted March 7, 2006 This post is of interest to me because my car does not have one and I didn't think the engine had been modified before I got to messing with it.... '83 turbo... So where exactly is this line that bypasses the thermostat and where does it draw it's fluid from. From how tonyd is talking, it seems like it is drawing fluid from a hot spot in the cylinder head to help make it cooler? Seems like the hottest spot on the cylinder head should be in the middle where the two exhaust ports are together. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted March 7, 2006 Administrators Share Posted March 7, 2006 ........Like I said earlier, Nissan put how many hundred-thousands of these bypass lines on, all unrequired on a street car---they just wasted their money because they like to use odd-bits of tubing and hose... C'mon, I'm not buying it! If they COULD'VE left it off and saved a $$$, they would have, the US Spec 240's didn't have Splash Guards or Fan Shrouds for gawd's sake. You think something that could be deleted WORLDWIDE across the ENTIRE L-Engine line would have been deleted if it was SO unrequired! Tony, I’m not trying to be rude here, but you did jump into this thread sort of “screaming” and posting with a demeaning attitude. Lighten up a little and just post your “theories” as you understand them in an effort to convey your idea in such a way that we would want to listen to you, not cram them down our throats with attitude. You will be more successful at getting your point across to others, (whether we agree with you or not), by communicating and explaining your theory, not ranting, raving and acting like a little kid who doesn’t get his way. Rest assured, we are listening and we honestly would like to fully understand your point, but please, quit trying to cram it down our throats, just explain it. As for the topic at hand and your theory that, “if Nissan designed and used a particular component or system, they did it for reason and it should be retained”, I offer this for thought…. On modern throttle valves, early ‘80’s and up, Nissan also added a coolant port to the throttle valves thus pumping 185+ degree coolant through and around the throttle valve. In fact, most, if not all auto makers are also doing this. (We tuners prefer to NOT preheat the incoming air charge). Nissan and all other automakers also installed Smog pumps on Z cars and spent LOTS of money in research and development, parts, manufacturing, etc on the smog pump. (We tuners prefer not to spend our engines Horsepower turning a pump that doesn’t increase our power output). Nissan as well as all other auto manufactures designed and used the EGR valve extensively… (We tuners prefer to keep the intake charge as pure as possible for maximum power, i.e. not diluted with inert gasses, there is already enough inert gas, Nitrogen, in the air that the engine must ingest as it is…). What do these components/systems have in common? They were all OEM designed and installed, with HUGES sums of money invested in R&D, manufacturing, parts, etc, but yet hot rodders from your weekend garage wrencher to your most successful tuner shops prefer not to use them. I think you get the idea I’m trying to convey here. Not ALL OEM ideas and designs are necessary or desirable for a performance engine, and even for some bone stock grocery getters, but if the car is a stocker, no sense in removing it right? FWIW, Rusch Motorsports eliminates the OE external coolant bypass on our engines that we build and/or install for most of our customers while utilizing a bypass such as the drilled thermostat, unless the customer wishes to retain the external bypass, then we leave it. . Quote Link to comment Share on other sites More sharing options...
briann510 Posted March 7, 2006 Share Posted March 7, 2006 We have stock radiator with 1 14" electric cooling fan and use water wetter and water only and we have yet to run any hotter that 200 degrees even on 95 degree days in traffic. Most of the time the fan isnt even turned on. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted March 7, 2006 Share Posted March 7, 2006 Just to stirr the pot a bit. On my old enigine I didnt have a bypass line. I had LOTS of issues with over heating' date=' then my engine blew up in a few different ways. Then again I also have an "anti-lion rock" sitting outside my house and I have not once had a lion attack my residence!-Warren[/quote'] I don't think you can really use this information. I run and F54 block with 280z internals with the coolant bypass valve and a ron davis AL radiator with twin cooling fans and my car still gets hot. I also run Redline water wetter to try to cool it. -Ed Quote Link to comment Share on other sites More sharing options...
bjhines Posted March 7, 2006 Share Posted March 7, 2006 I run an L24 in one of my track cars... I removed the coolant feed from the thermostat housing to the intake manifold when I installed earlier 4 screw carbys that did not have the coolant passages.. I have since installed triple DCOE45s and still have this port blocked off... It made absolutely no difference in temps on track in summer 95* days.. adding an oil cooler did not make much of a difference in coolant temps either... it sure keeps the oil pressure up though... I have installed a new heater core on this same vehicle and reconnected the lines as stock.... that made absolutely ZERO difference as well... of course i dont run the heater in the summer.. so I would not expect it to make any difference... The "bypass lines" are just there to heat the manifold quickly in winter... it is simply an emmisions related system... PLUG IT AND RUN.... there are plenty of people building race engines that will agree.... and present their opinions in a respectful manner... I mistrust anyone who arrogantly insists they are right and everyone else is wrong all of the time... that is a sure sign they have issues with truth and facts. Quote Link to comment Share on other sites More sharing options...
sonomaz Posted March 7, 2006 Share Posted March 7, 2006 My two cents worth. In my opinion, the external cooling line from the waterpump inlet (bottom radiator hose) to the back of the engine over to the carbs through the carb thermostat through both carbs and back to the underside of the thermostat housing is NOT a coolant return line for block circulation when the engine thermostat is closed. The purpose of the line is to heat the carbs to more effeiciently atomize the fuel to reduce unburned fuel out the exhaust pipe therefore reduceing tailpipe hydrocarbons. Something the EPA was very woried about in the 70's. Early Z's (69-70?) did not have them. Check Ztherapies web site. The thermostate at the back of the Carb's CLOSES at 170 degrees (boy, if I'm wrong I'm sure I'll hear about it). It closes so the carbs will cool to around 170. the reason Nissan spent so much money on these little items was so they could sell cars in the United States that met the EPA requirments. (ZTherapies sells Euro ballance tubes that have no smog fittings, so why in the US but not Euro? EPA!!!) Paul Quote Link to comment Share on other sites More sharing options...
sonomaz Posted March 7, 2006 Share Posted March 7, 2006 For what its worth? My 72 went 200K miles with the damned carb thermostat pluged and when the head was rebuilt it looked beautiful!!! OK 1 incident in 2 million engines. Quote Link to comment Share on other sites More sharing options...
briann510 Posted March 8, 2006 Share Posted March 8, 2006 Well I wouldnt argue with Tony on this as for the most part it is there for a reason as he pointed out quite clearly and factually and probably for the average owner should be left intact. I recall asking Tony for advise on this a couple years ago when I bought our Z and it was plugged off because it leaked. Quote Link to comment Share on other sites More sharing options...
bjhines Posted March 8, 2006 Share Posted March 8, 2006 for you guys who are experiencing cooling problems.... Take a closer look at your front cover, water pump cavity....there are some very thin/ close tolerance details in there that are commonly fubared when a water pump failed... many folks just fix the pump, radiator, fan, clutch... but they entirely miss the fact that the front cover is ruined as well... I had a 240Z with cooling problems... I eventually swaped front covers during head work.... and my cooling problems dissapeared... =================================================================================================== I have an oversize waterpump pulley and a 5" Moroso alternator pulley... The larger waterpump pulley made a noticeable improvement in coolant temps during track use(5k to 7kRPM)... but it made the engine overheat faster at stoplights in street traffic.. it also greatly decreased the effectiveness of my electric cooling fans in slow traffic... now I switch waterpump pulleys and belts for track events and street use. The MOROSO alternator pulley is for a 300zx lightweight alternator made by mitsubishi... it wont make power below 2kRPMs... it is now a 1 to 1 ratio... combine that with a tiny, deep cycle, race battery.. and the ignition can begin to have trouble at idle speeds with all the lights and accessories on... but I don't fry alternators twice a year either... there are always trade offs... race VS street use Quote Link to comment Share on other sites More sharing options...
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