IdahoKidd Posted December 19, 2009 Share Posted December 19, 2009 I have been chasing a poor/no heat issue in my 77 stock 280 for some time now. The engine temp has never come up even near mid point on the gauge all summer and now with winter, it is becoming an issue. Regardless of thermostat (180, 190,200), the water temp comes up to 160 ish as measured with a laser digital thermometer. With the upper radiator hose removed, there is a small trickle returning to radiator (engine running) There is no circulation from the block to the heater core other than gravity. It won't push it up a hose to a container, lower the hose and it will drain the radiator. Same for return line from heater core. Heater core is not blocked. I can blow through it easily. Looking into the radiator through the hole for the cap, there is water movement. Temp is reasonably steady at 160. Front of radiator is 100% blocked with cardboard. Car is in heated shop after being driven reasonably hard. Clutch fan seems to work (disengaged) I've been wrenching for some 30 years and can't figure it out. Water is getting around the thermostat and back to the radiator without going through the heater core. Something in a water jacket must be broken? or something in the head? or in the water pump? Seems to me a bad pump would let the engine get too hot though. Anyone ever experience something like this? Thanks! Leonard Quote Link to comment Share on other sites More sharing options...
olzed Posted December 19, 2009 Share Posted December 19, 2009 Could be an air lock in the block.I had very similar in my s30 Quote Link to comment Share on other sites More sharing options...
Tony D Posted December 19, 2009 Share Posted December 19, 2009 pump impeller gone Quote Link to comment Share on other sites More sharing options...
IdahoKidd Posted December 19, 2009 Author Share Posted December 19, 2009 It isn't the water pump. Took it off this morning and it looked like brand new. Put on a new one anyway. With the motor running and the temp gauge midway, water moving across the top of the radiator at 160, I took the both hoses off the heater core at the same time. No water in either one. So where do I look now? I am certain that this isn't correct. Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted December 21, 2009 Share Posted December 21, 2009 pump impeller gone If no water pump, the engine would have subsequently gone in the summer. As said engine is probably fine and should not be monkeyed with. Just because there is some flow to the heater core does not mean that: 1) the heater control valve is opening all the way or 2) the 70's vintage heater core is not 75% clogged up. Everything is pointing that the engine is fine. Start looking at the heater control and core if you have a heater problem would be my suggestion. "Blowing" through a heater core won't tell you if it's mostly packed off to fluid flow. Vintage heater control valves are notoriously sticky with age. Good luck. Quote Link to comment Share on other sites More sharing options...
IdahoKidd Posted December 21, 2009 Author Share Posted December 21, 2009 The heater is completely unhooked. There was no water coming from the back of the block. I high pressure back flush apparently dislodged something as it now has water circulaton through the heater (which gives me some heat). The existing problem still remains; the entire coolant system (all water in radiator) heats at the same time and never exceeds 160 (within a degree or two). It takes 40 minutes to get that warm. I can not stress enough it is not the thermostat. I can take the upper hose (thermostat to radiator) completely off. At least I can get the frost off the windows for now. I'll keep driving it until I can figure it out. Thanks and if something strikes you, PLEASE let me know. Leonard Quote Link to comment Share on other sites More sharing options...
MatMan Posted December 21, 2009 Share Posted December 21, 2009 Blockage in the head? Maybe something called "extrudahone" can unblock/smooth things out? Quote Link to comment Share on other sites More sharing options...
zedsn Posted December 21, 2009 Share Posted December 21, 2009 Sounds like you may have a bad rust or scale build up in the block or a prior owner tryed to fix his leaky radiator problem with stop leak and the stuff has traveled everywhere and left behind chunks in bad places. You are going to have to somehow flush your motor big time but that may just move stuff from one spot to another. The ideal thing to do would be remove the head and inspect head and block water passages. Good luck and I doubt there is an easy long term fix. Quote Link to comment Share on other sites More sharing options...
jasper Posted December 22, 2009 Share Posted December 22, 2009 How long have you owned this car? Did it ever operate properly? If so when/what changed? Pictures of the thermostats, coolant hose routing, heater hose routing would be helpful. I have seen many partialy clogged heater cores. Quote Link to comment Share on other sites More sharing options...
IdahoKidd Posted December 22, 2009 Author Share Posted December 22, 2009 Hey Jasper, I have had the car about 18 months. It has never come up to temp in the summer and only this year did I drive it in the winter. The car has a bone yard motor from PO that he never got started (passed away). It runs like a million bucks. The heater core was completely unhooked while trouble shooting. Took it to a semi retired datsun tech who admittedly hadn't worked on z's to any degree since late 70's. The only conclusion, and it isn't practical and may not even be possible, is that there is a crack or a break in the water jacket behind the water pump. It is the only way we can come up with to get circulation past (around) the thermostat. The plan now is to drive it till it breaks. If it does. Quote Link to comment Share on other sites More sharing options...
jasper Posted December 22, 2009 Share Posted December 22, 2009 If no overheating occured over the summer, then your radiator is funtioning properly. Engines CANNOT cool themselves in the summer. Cracks/impellers/ hose routing/clogged heads/etc cannot induce self cooling. Depending where you point the infrared gun, the color/finish/material/etc will effect the temp reading. This realy sounds like a clogged heater core, and clogged supply hose/tubes. Make sure the heater core supply hoses go to the correct locations,and the water control valve is fully open...visual inspection. Keep it simple. Quote Link to comment Share on other sites More sharing options...
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