datjunky Posted July 5, 2010 Share Posted July 5, 2010 I have a 70Z with a F-54/E88 mtr in it. New radiator, water pump, etc. When I start it up cold, the temp gauge rises to 3/4 briefly. Then goes back to the middle (normal). I sure thought it was a thermostat not opening correctly, so I put a new one in.. Same thing. The car runs at normal operating temp all day after that initial warm up. Whats the deal?? Thanks! Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 5, 2010 Share Posted July 5, 2010 What temperature in the thermostat housing corresponds to '3/4' on your gauge (everybody seems to have a different number). Verify the temperature, realize that cracking a thermostat (especially if you have your heater on in the morning) gives a RUSH of coolant through the back of the head and out the thermostat housing. You likely are seeing nothing more than the result of latent heat being taken out of the back of the head and the rest of the engine after the thermostat opens and REAL flow is established through the system. Up to that point, it's really only recirculating through 2 10mm bypass lines, and whatever you have hooked up going 'round' the back of the block! Thermostat opens and flow rate through the system skyrockets. Heat is removed in a rush. Sticking thermostat can do it as well, but you saw what changing a thermostat did... Quote Link to comment Share on other sites More sharing options...
datjunky Posted July 5, 2010 Author Share Posted July 5, 2010 What temperature in the thermostat housing corresponds to '3/4' on your gauge (everybody seems to have a different number). Verify the temperature, realize that cracking a thermostat (especially if you have your heater on in the morning) gives a RUSH of coolant through the back of the head and out the thermostat housing. You likely are seeing nothing more than the result of latent heat being taken out of the back of the head and the rest of the engine after the thermostat opens and REAL flow is established through the system. Up to that point, it's really only recirculating through 2 10mm bypass lines, and whatever you have hooked up going 'round' the back of the block! Thermostat opens and flow rate through the system skyrockets. Heat is removed in a rush. Sticking thermostat can do it as well, but you saw what changing a thermostat did... The thermostat is a 180. Id say its getting to around 200-210 on my gauge. It seems to vary a bit each time, as to how far it will climb before the thermo opens and cools things off. Ive never seen this in any of my other Z's. Not too worried as its hot only very briefly. Just seems a bit odd. Thanks for your response and explanation. Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 5, 2010 Share Posted July 5, 2010 You totally missed what I asked. Your reply gave what you thought the gauge was telling you. In reality, you have no clue whatsoever if that 'spike' is 160F or 230F. You need to verify the temperature with an independent gauge to determine if anything is wrong. The gauge in an S30 is as useless as teats on a boar hog. I wouldn't trust it as far as I can throw one! I have been driving in cars which were almost 'pegged' while an i'nfra-red scan showed 160F on the thermostat housing (and only slightly higher at the back of the head.) A Meat thermometer in the filler neck confirmed the I-R shots. Find out if you are truly 'spiking' or if you just have some dynamic in the response of the sender/gauge. My 260Z does this when I run the heater on COLD days. Yeah, it's 'overheating'...not! Time to time, not all the time. IR gun says 170 when it's 'spiked' and 160 when normal. Running the highway at 110F ambient, the same gauge spot is 210 (actual) should I cover 3/4 of the radiator with a plastic bag from the freeway updraft... Quote Link to comment Share on other sites More sharing options...
datjunky Posted July 12, 2010 Author Share Posted July 12, 2010 Understood.. I dont have a surface temp reader or another gauge handy.. but, just this morn it did boil over.. it climbed to what would be around 220-230 on the gauge, i pulled over and lifted the hood.. puked antifreeze out the overflo. it had not done that before, nor had it reached that high on the gauge. it sure seems like a faulty thermostat. the first one was whatever MSA sells, the one in it now is a NAPA one.. im going to order a Nissan part and see if I get the same results.. not sure what else to try. the car runs great other than that initial spike. goes down the freeway at around 195 on the factory gauge in 90 degree temps @80mph. Quote Link to comment Share on other sites More sharing options...
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