Beaver Posted January 9, 2013 Share Posted January 9, 2013 The last two times Ive driven long distances (ie over an hour) the water temp does funny things. It generally runs just above halfway on the gauge and donest change much. Ive noticed that after some time (about an hour or so), the temp gauge will rise up to about 4/5s for around half an hour or so, then it will quickly drop back to half way. By quickly I mean you can see the needle drop and it takes about 5-10 seconds. it then wont change (much) again. I get track of this the sexcond time it happened and I hadnt chnaged the way I was drivintg, and it was all nice open straight roads doing 80-100km and nothing had chnaged when it suddenly dropped. Could the sender be playing up? or could it be the thermostat doing something funny? Any other ideas? This is the first time I have really noticed it moving around, and have done 2000 odd kms in the last few weeks. The first time I thought it was just reposnding the the drive (slow and windy) but then once on the open straight road it didnt come down. Cheers Quote Link to comment Share on other sites More sharing options...
Seedy Al Posted January 9, 2013 Share Posted January 9, 2013 Water levels staying ok? Sounds like it might be thermostat to me, but well, you never know. Also consider a blocked radiator, however I'm suprised that it would only do it on straight roads Next time it does it, pull over while its still high and check temp of both radiator hoses, and maybe surface of radiator Quote Link to comment Share on other sites More sharing options...
KKtrips Posted January 9, 2013 Share Posted January 9, 2013 Sounds like the thermostat could be shutting when at cruise because the radiator is overcooling the system. Get one with a lower opening temp say 72 degrees (I guess you most probably have a 82 degree stat in it at the moment) Quote Link to comment Share on other sites More sharing options...
evil_si Posted January 9, 2013 Share Posted January 9, 2013 My money is on the thermostat Quote Link to comment Share on other sites More sharing options...
Beaver Posted January 9, 2013 Author Share Posted January 9, 2013 Water level is sweet, doesnt use a drop. Rad is recored (few months ago) so I dont think itl be blocked, but ill give it a flush anyway (probably due for one). I did the thermostat and water pump a few months back (when rad was done) and the new thermostat was 82, the original 80. I dont think its related to the cooling ability/lack of ability (thermostat excluded) as when the temp was high it woudlnt change it I was just cruisign or slogging up hills etc, so thermostat sounds about right. Another thing I though was odd (I may be wrong) is that there is bugger all/next to no pressure in the system....like whenI first happened I grabbed a towel and prepared for an explosion as I took the rad cap off but there was just a small fizz and then the cap came off straight away. SHoudl there be decent pressure or is that just once things start getting toooooo hot? Cheers Quote Link to comment Share on other sites More sharing options...
KKtrips Posted January 9, 2013 Share Posted January 9, 2013 Should be decent pressure in there. How old is the rad cap? Most probably pay to throw a new one of those in if it's not new. I feel that if you chuck in a 72/76 degree stat and it will be sweet on the temp side., Quote Link to comment Share on other sites More sharing options...
Beaver Posted January 9, 2013 Author Share Posted January 9, 2013 Likely the original one....lol, will grab another as well as a lower thermostat cheers Quote Link to comment Share on other sites More sharing options...
KKtrips Posted January 10, 2013 Share Posted January 10, 2013 If you get it from Repco and they are playing dumb buggers then what you want is a TT160 (Tridon Thermostat 160degree *farhenheit) which is 72 degree I think. I expect your current one will be TT180. Quote Link to comment Share on other sites More sharing options...
Beaver Posted January 10, 2013 Author Share Posted January 10, 2013 lubs Quote Link to comment Share on other sites More sharing options...
Slacker_Sam. Posted January 10, 2013 Share Posted January 10, 2013 And if you get a Dayco stat chuck it in the jug to make sure it works. I've had a few dud ones come back for warranties lately..... Quote Link to comment Share on other sites More sharing options...
Evan Posted January 10, 2013 Share Posted January 10, 2013 change the sender/sensor thing. cheapest and easiest option before you start ripping into other things. Quote Link to comment Share on other sites More sharing options...
KKtrips Posted January 10, 2013 Share Posted January 10, 2013 Yes it's cheap and easy but unlikely. Quote Link to comment Share on other sites More sharing options...
Evan Posted January 10, 2013 Share Posted January 10, 2013 I had a similar problem in the past with the temp gauge doing strange things (on the open road) turned out it was the sender/sensor plug thing. Worth a shot in my book. Or just do em both. EDIT: the time its taking for the thermo to open/close/open again seems... long, even if its a higher temp one or slightly bung. Quote Link to comment Share on other sites More sharing options...
sholdowa Posted January 10, 2013 Share Posted January 10, 2013 Lack of pressure is a big worry. Maybe try running without a thermostat - no problem at this time of year - and the heater on (!) and see whether the system pressurises / level drops. Maybe there's an airlock in there somewhere? Quote Link to comment Share on other sites More sharing options...
CaMpylobacter Posted January 10, 2013 Share Posted January 10, 2013 I wouldn't go lower temp in the thermostat. you're not having overheating issues, it's just your thermostat sticking as your radiator overcools for the conditions. as you hit a windy spot or give it beans, it needs to use the radiator 'constantly' to maintain temperature. when cruising the thermostat will jsut be popping open a little bit and trickling hot water through the rad but otherwise pootling along with it mostly shut. every now and then it's sounding like it's sticking for a while then opening right up. my pajero when i got it would go nicely to halfway on the gauge after a cold start, stay there for 5 minutes or so, then suddenly, like yours, you could see the gauge moving down, and it'd settle a gnats dick width above the cold line. new thermostat, sorted. Just chuck a standard thermostat in it. 120y datsuns aren't known for having under specced cooling systems, plus you have a new radiator and waterpump from memoery so jsut leave an 82 degree one in it. you'll thank yourself in wintertime if you do this. radiator caps are like $8 at trade so slam a new one on. You may have little pressure after your episodes happen (esp if you have no header tank) as the coolant expands as it heats. you can't compresse water so it expels the excess(which may be a little air... may be nothing at all), then when it cools down it shrinks, thus the pressure as set by the cap cannot be maintained. when you start the car cold again it starts again and lets a little pressure build. hard to explain but yeah. Quote Link to comment Share on other sites More sharing options...
KKtrips Posted January 10, 2013 Share Posted January 10, 2013 Knowing that the t-stat in Beave's car is quite new then my theory is not blaming an ineffective cooling system - it's based around the fact that the cooling system is too effective. My theory is the water cools from the lengthy periods of cruising speed and is slowly closing the thermostat.. While the t-stat is closed and the water is heating up in the block again - the water in the radiator continues to get even colder. The water gets so cold that when the water in the block gets to opening temp, the super cool water on the rad side holds the thermostat closed for just a little bit longer until the water in the block finally gets hot enough to overcome the cold water effect on the rad side and the thermostat opens suddenly. Getting a lower temp thermostat is not to make the water have cool water enter the block faster when heating up - it's so the thermostat stays open longer when the engine is cooling down. The chances of the cooling system being effective enough to cool circulating engine water down to 70 degrees (closing temp for a 72 degree t-stat) is fairly unlikely whereas it getting down to 80 degrees (closing temp for an 82 degree t-stat) is entirely possible.. I hope that makes sense - it's quite difficult to explain what I mean but I think that gives an idea.. Quote Link to comment Share on other sites More sharing options...
Rookie Posted January 10, 2013 Share Posted January 10, 2013 I think you two are talking about the same thing. I have had brand new thermostats that are faulty, so I personally would change it for another stock temp one. Quote Link to comment Share on other sites More sharing options...
CaMpylobacter Posted January 10, 2013 Share Posted January 10, 2013 yeah. would maybe be worth boiling it up to check it opens then whack it in some cold water, then back to the pot to see what happens? I dunno glad you esplained what you were saying about, chris thanks It miffs me a little when people do all they can to get their car running as cold as possible, is all. It doesn't improve anything! Quote Link to comment Share on other sites More sharing options...
Rookie Posted January 10, 2013 Share Posted January 10, 2013 You sound like Colin Chapman hahaha he was all about his cars running at 102°c hahah Quote Link to comment Share on other sites More sharing options...
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