cygnusx1 Posted June 25, 2007 Share Posted June 25, 2007 OK here is a strange problem that my Z has had for a while. It runs cold. The dash gauge peaks at dead center and stays there if I drive the car hard or semi-spirited. As long as I return to normal speed limit driving, it runs about 1/3 on the gauge. Megasquirt, and the Nissan head temp sensor, comfirm the dash gauge reading. It hangs between 150-160F if I drive it casually. I already changed the thremostat (180F rated) and that made no difference. The temperature adjustable e-fan only comes on when the needle goes past center, about 195F, and goes off at about 180F or so. When I cruise 40-50mph and even 60-70 on the highway with light throttle, it runs right back down to 150-160F. My front is basically stock (no ducting) with the urethane air-dam, Intercooler-oil cooler-AC Condenser-Radiator, all stacked sandwich style in the nose. The waterpump is new. Any ideas what could be wrong? EDIT: you can actually see the needle a little in the sig pic. It's running cold there too. Quote Link to comment Share on other sites More sharing options...
oinojo Posted June 25, 2007 Share Posted June 25, 2007 i have the same thing going on. When my motor was carbeurated it stayed dead center. Now that i have the l28et FI stuff it stays chill at 1/3 guage. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted June 25, 2007 Share Posted June 25, 2007 Put a piece of cardboard in front of the radiator? Why are you worried about it? Does it run poorly at that temp? One thing that might help is a theromostatic control valve on the oil cooler. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 26, 2007 Author Share Posted June 26, 2007 Well I am not worried about it too much but for proper combustion it should be at the right temperature. If it was the stock FI system, it would run rich when it was cold. You think the oil cooler is pulling down the water temp? I will try the cardboard trick. If that works then I'll start thinking about some sort of front end aero ducting like the Wind Tunnel testing showed. Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 26, 2007 Share Posted June 26, 2007 Oil Cooler? If your oil cooler is thermostatically controlled then no. If it is an 'all through' cooler, cooling everything it is a BAD thing! I have said this many times before: Water temperature is a VERY POOR indicator for what is going on in the engine. It has a lot of specific heat and really slowly responds. Water temperatures were usually set (in the old days) to keep oil temperatures around 180 degrees of hotter. Monitor oil temperature, and regulate it with a thermostatic valve to 180 or higher. Let the water run as cool as it is. If you really have a 180 degree thermostat it's closed, and you are simply recirculating coolant in the block, and through the bypass hose. It doesn't start to crack till 175-180, and isn't fully opened till at least 10 degrees above that. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted May 19, 2008 Author Share Posted May 19, 2008 REVIVAL of an old post with a possible culprit and solution! Tony D, I think after reading all the posts about cylinders 5 and 6 being hotter and coolant bypass information I realized whats happening. Without the hot water hose that heats the throttle body and fast-idle air actuator, you get no bypass at the thermostat housing. This will cause the water pump to force coolant past the thermostat and into the radiator when no additional cooling is required. (ie. light load, mid and high rpm cruising.) Tonight, I will reconnect a hose that runs water from the thermostat bypass fitting to the lower inlet on the passengers side. I bet the problem of cold running goes away. Another loose end in the Z tied up! Quote Link to comment Share on other sites More sharing options...
zmaster Posted May 19, 2008 Share Posted May 19, 2008 is a 160 degree thermostat too cold to run on a 75 280z? I can get 4 thermostats a 160, 170, 180, and a 190 thermostat. Quote Link to comment Share on other sites More sharing options...
Nigel Posted May 20, 2008 Share Posted May 20, 2008 REVIVAL of an old post with a possible culprit and solution! Tony D, I think after reading all the posts about cylinders 5 and 6 being hotter and coolant bypass information I realized whats happening. Without the hot water hose that heats the throttle body and fast-idle air actuator, you get no bypass at the thermostat housing. This will cause the water pump to force coolant past the thermostat and into the radiator when no additional cooling is required. (ie. light load, mid and high rpm cruising.) Tonight, I will reconnect a hose that runs water from the thermostat bypass fitting to the lower inlet on the passengers side. I bet the problem of cold running goes away. Another loose end in the Z tied up! So, did you actually test and verify this? My Z runs cool too (I think I posted about this at some point), but I have a hose going from the lower thermostat housing, through the turbo, and into the return line for the heater core. Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted May 20, 2008 Author Share Posted May 20, 2008 I was going to test it last night but didn't get to it. I will definitely try it one night this week and report the results. I can't think of any other reason why the engine would run colder than the thermostat considering the thermostat was replaced and then tested. Quote Link to comment Share on other sites More sharing options...
Nigel Posted May 20, 2008 Share Posted May 20, 2008 I can't think of any other reason why the engine would run colder than the thermostat considering the thermostat was replaced and then tested. Like Tony suggested, I'm thinking it's the oil cooler... Nigel Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted May 20, 2008 Author Share Posted May 20, 2008 I don't doubt Tony D or your advice at all but I tried covering up my oil cooler with cardboard and there was no difference. Besides it's a pretty small cooler and I can't see that dragging the water temperature down so quickly. The temperature gauge will go from normal to 1/4 cold in 1 to 2 minutes of low load cruise. The gauge works. I tested it with a thermometer. To me it seems that cold water from the bottom of the radiator is getting to the gauge sender. Quote Link to comment Share on other sites More sharing options...
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