blackbomber Posted December 27, 2014 Report Share Posted December 27, 2014 So ,heres the deal guys...I want to say first thanks for everybodys help....as far back as I can remember, the coolant res has been shot. cracked and full of holes, so its been out of use for like a billion years..the cap has been sitting on top of the res, with the line running to the radiator.So, since I have been taking better care of the truck, I decide to repair the reservoir...so I get all the holes patched up because a new one is like a billion dollars.. So , get it fixed, and get it back in, and fill it up to top level, and forget about it...cool right? wrong..so I am working on the alternator deal, and I see smoke or steam coming off the radiator, then I notice the radiator, and top hose are super hot, and the thermostat isn't even open yet, I mean like smoking hot, so I turn the truck off, and go back to cleaning the contacts on the alternator.... after the truck cools down, first I notice all the coolant has been sucked out of the reservoir...its just been sucking it in..so I pop the radiator cap, and its super full, above the cap level, so oh yea, I forgot to tell you guys, also, last few days, new knocking noise started, which I think is the water pump.so anyway, I got my syringe and started the truck, and started sucking coolant of the top of radiator, and got it back down to the level it was before, which is about a quarter inch above the baffles in the radiator.....the reservoir cap is laying on top, of the reservoir, like is was before... so, I didn't help anything, and now I have a new noise in the water pump....should have left it alone...something wasn't handling a full system..I thought the system was supposed to equalize itself, and not allow it to get to full, like isn't that what the res is supposed to do???? and keep the air out???? I don't get it ....so, that's it guys....I thought about closing off the line from the reservoir, but I haven't yet..... 1 Quote Link to comment
datsunaholic Posted December 27, 2014 Report Share Posted December 27, 2014 The job of the radiator cap is to prevent the cooling system from getting too much PRESSURE and blowing up hoses. The old way was to simply vent the radiator right to the road, which Datsun trucks did up to around '77 or so. The idea with the expansion tank (overflow bottle) is that when the system gets hot, the pressure goes up and the coolant expands, so it needs somewhere to go, and rather than dumping it on the road it pulls it into the bottle. Once it cools down, the vacuum in the radiator makes it pull the coolant in the bottle back into the radiator. So being full to the absolute top isn't uncommon- my Pathfinder, it's ALWAYS right at the top.In fact the only time it isn't, the overflow bottle is bone dry, which only was when I got it. As for the hoses getting extremely hot and the thermostat not being open, that's not a good sign at all. Usually means the thermostat is stuck. Rattles from the water pump aren't good either, if you grab the pully, does it wobble around? That's the sign the pump bushing is failing and the pump WILL start leaking and WILL seize if you let it run like that very long. I've nearly ruined 2 radiators from pumps seizing and throwing the fan into the radiator when they broke. One let go without much more than 5 seconds warning, but the other was rattling for a while before it went. 1 Quote Link to comment
JoeCool Posted December 27, 2014 Report Share Posted December 27, 2014 I would definitely start by replacing the thermostat. 1 Quote Link to comment
datzenmike Posted December 27, 2014 Report Share Posted December 27, 2014 Fixing the reservoir should not cause the rad to over heat so this must have been happening before and you didn't notice it. Very unlikely that the time you fix this another problem starts. Now there's no way YOU can tell if the thermostat is not open, nor can you say it was super hot. HOT is subjective and unless you can compare it to another time or have an infra red thermal heat gun, let's just say that the engine was up to normal operating temperature... which is only about 15 degrees below boiling, and I'd call that super hot. Let's not jump the gun (for now) and assume that the engine temp is normal until we have proof otherwise. Normal rad level is not 1/4" above the vertical tubes. On a coolant recovery system, its FULL to the top. BTW: The rad cap on a coolant recovery system is special and an ordinary one won't allow coolant back in. If a coolant recovery system is working properly, and you open the rad drain plug at the bottom, water will siphon from the coolant recovery reservoir into the top of the rad. Any container will serve as a coolant recovery reservoir as long as the hose is submerged. Any air in the cooling system will always fid it's way to the highest point... which is the top of the rad. Next time there is a heat spike after shut down and water 'burps' out, that air will go too. When cooled down only coolant will be allowed in. The knocking noise could be anything. Usually a pump or any other ball bearing, growls as it goes bad. 1 Quote Link to comment
blackbomber Posted December 28, 2014 Author Report Share Posted December 28, 2014 thanks guys,I will get back to you on this. need to re read the posts....give the info time to soak in....did I tell you I jumped the truck once, actually twice..It covered about 25 feet distance.... I was 20 years old, and I thought I could race in the Baja..... 1 Quote Link to comment
datzenmike Posted December 28, 2014 Report Share Posted December 28, 2014 At least the 720 has a collapsible steering column. 1 Quote Link to comment
blackbomber Posted January 6, 2015 Author Report Share Posted January 6, 2015 hey guys, starting to think maybe it is the thermostat.. I noticed tonight the radiator and cap and upper hose were super hot again...ie way hotter than they normally are. like not normal operating temp... and when grabbed the lower section of the lower radiator hose it was cold....also ,, I haven't been running the heater, because I have been trying to save power since I haven't got the alternator replaced yet... so the truck always runs hotter when I don't have the heater running anyway... uh don't know if I will make it through the winter....is it easier for the thermo to open when the fan is running??? { that new frontier is looking good}}... black bomber.... old datsuns never die...... Quote Link to comment
MikeRL411 Posted January 6, 2015 Report Share Posted January 6, 2015 When the heater is "on" you have a "free" secondary radiator, free heat dissipation! You don't need the fan if your heater intake plenum is not full of leaves and pine needles to get some free relief, the fan does help though! Quote Link to comment
datzenmike Posted January 6, 2015 Report Share Posted January 6, 2015 hey guys, starting to think maybe it is the thermostat.. I noticed tonight the radiator and cap and upper hose were super hot again...ie way hotter than they normally are. like not normal operating temp... and when grabbed the lower section of the lower radiator hose it was cold....also ,, I haven't been running the heater, because I have been trying to save power since I haven't got the alternator replaced yet... so the truck always runs hotter when I don't have the heater running anyway... uh don't know if I will make it through the winter....is it easier for the thermo to open when the fan is running??? { that new frontier is looking good}}... black bomber.... old datsuns never die...... Before fixing the over flow reservoir (or coolant recovery) the coolant level was likely low in the top rad hose so it wouldn't feel that hot. Now that it is full of hot water it only seems super hot. To end this discussion about subjectivity, borrow an infra red gun and shoot the thermostat housing and the upper rad hose when it's 'super hot' and you will likely find that it's about 180-190F I would definitely start by replacing the thermostat.. I think I would do this also. Your thermostat may work but it may be a little slow, or sticking or who knows. Get a good $12 name brand. 1 Quote Link to comment
blackbomber Posted January 6, 2015 Author Report Share Posted January 6, 2015 thanks mike, ok,,, Quote Link to comment
datzenmike Posted January 6, 2015 Report Share Posted January 6, 2015 I could be wrong, but what you are experiencing is probably normal operation. Quote Link to comment
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