1983 720 Not Getting up to Temp.

[Benannah]

My 1983 720 is not getting up to temperature. Only time it got to half way was on the highway when it was 90 degrees outside. Thinking it would be thermostat stuck open? I also noticed the radiator fan is always engaged. How do I resolve this? Thanks!

[datzenmike]

Change the thermostat and don't be cheap on it. No WallMart specials. A $4 part could leave you stranded somewhere.

 

The clutch fan should always be spinning. It has a 'fluid drive' just like a torque converter and it's top speed is designed to be limited by the slip. Engine off, try to spin the blade with your fingers. There should be firm resistance and it should stop as soon as your fingers let go.

[Benannah]

Thank you for the advice! I confirmed that the fan is functioning exactly as you described. As for the thermostat, what temperature should I get and how hard is it to replace? Do I have to flush the coolant? Thanks!

[datzenmike]

If you coolant is over three years old or you don't know how old it is I would drain completely and refill with a 50/50 mix of antifreeze and distilled water. Not only will this prevent a freeze up but it will prevent rust and hoses will last longer. Distilled water has no dissolved minerals and this will prevent kettle scale inside the radiator.

 

Drain about a gallon of coolant out of the engine. Follow the top radiator hose back to the thermostat housing on the side of the intake manifold. Two bolts hold the thermostat cover on, remove and lift old thermostat out. Clean both mating surfaces, install new thermostat with 'jiggle valve' up, at 12 o'clock. Put new gasket on, does not need sealer. Refill cooling system. Run engine till temperature gauge reaches half or just over on the gauge. Carefully remove radiator cap and top up with distilled water antifreeze mix. Any air bubbles will always work their way to the highest point in the cooling system which is the radiator cap. Check again after it has been run and cooled down. Your coolant recovery container should be half full with water anti freeze mix also.

 

[Thomas Perkins]

To check to see if your thermostat is stuck open.Remove radiator cap when engine is cold.Start up and see if the coolant in radiator is recirculating.If it is not,let run till it does and see where your temperature gauge is at.Could be your gauge,your temperature,sender or sender.Also your thermostat is  opening before the recommended temperature.I use 180 degree one on mine.Everytime I change my coolant,I change the thermostat.If you don't plan on changing your coolant just drain enough to get below the thermostat.If you remove the coolant,remove the lower radiator hose and catch it with a 5 gallon bucket.Way faster.I never ever have used my drain plug.Always check a new thermostat to see if it opens right on a stove top.Another thing is a bad water pump.

Edited October 19, 2024 by Thomas Perkins

[Thomas Perkins]

It is getting harder and harder to find local Auto Parts that have our parts in stock.One store may have the thermostat but no gasket.It may be the one with the wrong temperature range you want.So always buy 2 if you can.I have a few of each.Make your own from a Captain crunh cereal box.

Edited October 19, 2024 by Thomas Perkins

[Benannah]

Thank you for the help! I’ll just drain it up to the intake as I just flushed the system a couple weeks ago. I’m pretty certain the temp gauge works since while flushing the system the needle did go past half way while we were filling it, but never goes past otherwise.

 

On rock auto I saw that I could get the whole housing with a gasket for an additional $10. Do you think it would be worth it or just replace the thermostat?

[Thomas Perkins]

Just a thermostat.I have brand new Nissan outlet one still in the box with gasket.It's a keeper.

[Sephakrid]

I'd also suggest just replacing the thermostat unless the housing is corroded. The pre-cut gasket I got from Napa wasn't a perfect fit so I ended up buying a roll of gasket material and making my own (using Mike's hole punch suggestion). No leaks, no sealant used.

 

[Thomas Perkins]

19 minutes ago, Sephakrid said:

I'd also suggest just replacing the thermostat unless the housing is corroded. The pre-cut gasket I got from Napa wasn't a perfect fit so I ended up buying a roll of gasket material and making my own (using Mike's hole punch suggestion). No leaks, no sealant used.Looks good.

 

 

[datzenmike]

1 hour ago, Benannah said:

Thank you for the help! I’ll just drain it up to the intake as I just flushed the system a couple weeks ago. I’m pretty certain the temp gauge works since while flushing the system the needle did go past half way while we were filling it, but never goes past otherwise.

 

On rock auto I saw that I could get the whole housing with a gasket for an additional $10. Do you think it would be worth it or just replace the thermostat?

 

To see if the gauge works, ground the Yellow/Black wire on the sender with ignition on. Gauge should read full scale HOT.

 

Unless your top cover is damaged all you need change is the thermostat. 180-185F is fine.

 

To be sure the top cover has a smooth flat surface I glued some 180 sandpaper to a sheet of glass and pushed it back and forth. This is for an L series but same idea...

 

[Benannah]

Thank you for the help!

[dukerollo]

I had the same problem. The thermostat was stuck open. They are cheap, give it a shot before digging deeper. My radiator cap was also bad and never venting. Also worth changing out for what they cost. 

[Benannah]

Just wanted to thank all of you who helped! I just replaced the thermostat and it now gets up to proper temp and stays there very nicely! The old one didn’t seem obviously stuck open, but hey, the thermostat was cheap and something was wrong with the old one. I ended up buying some gasket material as well and cutting my own. So far works great! Thank you!