View Full Version : 85 nissan 720 help....

02-22-2009, 09:07 PM
I have my beater 720 up and running again it blew a head gasket... I love aluminium heads :thumbsdow . Anyways ever since i rebuilt it the engine refuses to warm up to operating temperature. It has a brand new radiator with no fan shroud I don't know if that would have any effect or not. Also i put a new thermostat in with the rebuild and then recently put another one in thinking maybe the first one was faulty. What do you guys think? coolant temp sensor? Or would the lack of a fan shroud cause anything?

02-23-2009, 05:29 AM
eh id test the temp sensor

02-23-2009, 06:14 AM
Sorry to be a noob but how do i do that? its not in my crap ass chilton manual

02-23-2009, 04:24 PM
I say drive it for a while. Give it plenty of time to warm up (a solid half hour or more). Then just feel the hoses or the radiator to see if it's warm (make sure the engine is off, you don't want the fan to slice your hand off). If the radiator and hoses are hot, then it's probably the temp sensor and/or gauge. If the radiator and hoses are cool, then it's something else.

Not having a fan shroud should actually make the engine run warmer, not cooler, since the fan is less effective at pulling air through the radiator.

02-23-2009, 06:14 PM
The engine gets warm. I installed an aftermarket gauge thinking maybe the factory one wasn't working but it only runs at 140-150 at the very most it should run around 180

02-23-2009, 09:43 PM
then I'd try the temp sensor. Or, perhaps just block off part of the radiator with cardboard. That's what we do up north to help a vehicle reach operating temp when it's -40 outside.

02-23-2009, 09:49 PM
I've never even heard of a 720.


02-23-2009, 11:22 PM

It sure isn't a pretty thing but i gets around off road and in the snow.

02-24-2009, 03:41 AM
Anyone else.. help?? i dont know what to do its on its 2nd thermostat. Its not like its that cold here its like 40's at the lowest so something else is going on... i am stranded. would changing the coolant temp sensor have an effect? blocking off the radiator wouldn't work because it wont even warm up at a stand still

02-24-2009, 04:20 AM
Does it drive?

02-24-2009, 04:23 AM
yes, but its aluminium head and i'm pretty sure its what caused the head gasket to blow. these things are notorious for blowing and i really want to fix this problem so i can drive it.

02-24-2009, 04:14 PM
Well, I looked up "overcooling" in my repair manual and it only listed two possible causes:

1. Thermostat Faulty
2. Inaccurate Temp Gauge

Since you've already got a new gauge, I would replace the sensor. Then I would burp the cooling system again, just to make sure you don't have any bubbles that might be affecting your readings.

Keep in mind, it's better to be running too cool than too hot, so I wouldn't be worried about the head warping and blowing another gasket. I'd be more worried about excessive wear caused by slightly thick oil.

Also, blocking off the radiator still might work, even if it doesn't warm up while sitting still, because I imagine you have a mechanical fan that is spinning all the time and pulling air through the radiator all the time. Once you get the sensor replaced it's worth a try.

02-24-2009, 07:10 PM
You would be correct about the fan it spins full time. One thing i have considered doing is getting an electric fan and wiring it to some sort of coolant temp module. I'm not entirely sure how to do it or if its possible but it seems like it could work, right? I am a little concerned with the undercooling because the last time it blew it was running cold and never overheated, this engine is one of those 40,000-50,000 mile import ones. So it shouldn't have blown already i only put about 1,000-2,000 miles on it. So your saying i should try replacing the coolant temp sensor? Does that control the temperature of the engine at all? i was under the impression that it just read temperatures.

02-24-2009, 09:40 PM
All it does is read temp. It's possible some of the car's computer systems will use that temp reading to adjust various settings, but that's unlikely on such an old car. The point of replacing the sensor is that it's possible that the car is warming up just fine (or even overheating), but a bad sensor is giving you the low reading.

I would also be sure to burp the cooling system again, because it's possible that an air bubble is blocking flow to the sensor, and throwing your reading off (as well as possibly causing an overheating condition).

Yes, hooking up an electric fan to the temp sensor is possible, and if you have a little bit of electrical knowledge, fairly simple. You'd just have to set up a switch that's programmed to connect current to the fan when the operating temp voltage is being sent from the temp sensor. What that voltage is, I don't know. But it's definitely doable.

I would start with burping the cooling system, then replacing the sensor first, though.

02-25-2009, 12:41 AM
i converted my ae86 to electric fan and used a stock toyota fan temp switch and a stadard automotive relay. use the temp switch to trip the ground on the relay and bam on come mai fan.

02-25-2009, 02:27 AM
Ok well i have an aftermarket gauge and it is tapped into the intake seperately so there is no problem with the reading and by the way it is running it is not overheating i can feel that it is running very cold. How do i burp the cooling system i have never done that.

02-25-2009, 02:14 PM
1. Turn the heater control to max heat.
2. Add coolant to the radiator slowly and reservoir till both are full.
3. Leave the radiator cap off and run the engine till the thermostat opens (coolant starts flowing and the upper hose warms up).
4. Shut off the engine and let it cool. Refill the radiator and reservoir.
5. Squeeze the upper hose to expel air. Then add more coolant as necessary.
6. It couldn't hurt to repeat the procedure to be sure.
7. Replace the cap, start the engine, look for leaks, and hopefully it works.

If it's apparent that the coolant is flowing right away, before the engine has a chance to warm up, then the problem is the thermostat, and I'd try replacing it again.