quick to overheat

[Chance]

I recently just replaced the exhaust manifold gasket and carb gaskets and it runs good but it overheats very quickly and it doesn't stay cool I flushed and replaced the coolant. also i have to have my distributor all the way maxed out to get to 8 degrees advanced and it still runs at very low rpms so I did about 12 degrees and its bit better but literally everything is to the max on tuning for it to run at like 750 rpm 

[ggzilla]

After changing the coolant, most engines will overheat. Unless you bleed the cooling system. After running it to max temp, top up the coolant in the radiator

 

5 minutes ago, Chance said:

i have to have my distributor all the way maxed out to get to 8 degrees

Should be able to get it to 20btdc. Is there not enough slot left to rotate the distributor?

[Chance]

58 minutes ago, ggzilla said:

After changing the coolant, most engines will overheat. Unless you bleed the cooling system. After running it to max temp, top up the coolant in the radiator

 

Should be able to get it to 20btdc. Is there not enough slot left to rotate the distributor?

I bled it and its topped off ill go drive it around to see if it overheats again. 

 

yea there's no more slot left on either adjustments on the distributor and that barely gets it to 8 degrees advanced 

[banzai510(hainz)]

1 hour ago, Chance said:

distributor all the way maxed out to get to 8 degrees advanced and it still runs at very low rpms so I did about 12 degrees

If you barely got 8deg how you get 12deg???????????

As Gzilla says you should be able o get 0-25deg with turning the dist using a timing light.This would be a timed dist and not off a tooth. Now if off a tooth it be hard to get 8deg. then goes out of time as rpms go up.  remeber you have a idle mixture adjustment also at the base of the carb,the one with the tension spring. turn this in out till best running and get it timed and then maybe add the carb speed adjustment. all in combonation

 

After a coolant change as Gzilla say there could be a air bubble or something esp if this was running fine before. I ran into soem young guys recently and they said their 620 was running kinda hot. They just go the rig. I felt the radiator and it was cold to the touch I said WTF. I was stumped right off. I took a rag and pop the cap and instantly the rad got HOT.  I told them to get a Rad cap with the flip red lever to help get the air out. But I dont know if I was lucky or it really fixed the proplem but it was a 3 core alum rad so it should have been cool. Also they had the Boursin distributor and I dont kow if it was timed correctly as he too had to slot the dist timing plate. For soem reason I use the Rad caps with the red pressure lever( I still have a hose to a catch bottle/MountainDew ect....). My newer vehicles I had the standard type caps with the recovery system and they seem fine. Dont have proplems with my 91and 92 pickup since I changed both rads recently.

[Chance]

okay so here's whats happening I have a timing light where you can select what degree advance you want and I had at 8 but its really set at 16 degrees since I had it set. I just took it for a drive and it didn't go all the way hot like it did before, this time it stayed at around 75% on the gauge. the problem is if I turn the distributor down to 8 degrees it will be too low rpm and too lean which I think is why it was running overly hot the first time. 

Edited July 30, 2025 by Chance

[ggzilla]

Best to set the timing light to 0, and check the timing mark on the engine cover

 

Timing is the base setting, so after setting the timing, adjust the idle speed and then the idle mixture

[datzenmike]

Then check the timing again or last. Idle speed too high can introduce vacuum advance, I guess you could disconnect the hoose but if idling at right RPM there shouldn't be any vacuum advance. Vacuum advance depends on the position of the throttle plate. 

 

Then there's mechanical or centrifugal advance. The '73 begins at about 850. If you have a tach in the timing light make sure you are below that. I don't know the idle speed for the L16 but 650 to 750 sounds about right.

[Chance]

got the truck running at around 750 at 8 degrees advance with a little room to advance it a bit more. we'll see today if it over heats. I am going on an 8 hour drive coming out of phoenix which is pretty hot and then ill be more north where it will be about 90-94 degrees but I want to make sure the truck stays cool and runs cool any tips would be appreciated to help with that I'm changing the oil and getting some new spark plugs. I leave tomorrow. Thanks Y'all

[hobospyder]

get a sprayer bottle from harbor freight and fill it with water. grab some extra hose and run it out to the radiator and while driving spray some water on the radiator every now and again. 

[NC85ST]

1 hour ago, Chance said:

I want to make sure the truck stays cool and runs cool any tips would be appreciated

If you’re still having the issue described in the beginning, running hot, leave the truck at home and drive something else. Nothing would be worse than being 8 hours from home with a blown head gasket from overheating.

[Chance]

1 hour ago, NC85ST said:

If you’re still having the issue described in the beginning, running hot, 

whats a normal range for the gauge to be in mine gets to like 75% then stays there.

 

[Chance]

and this was in 110+ degree heat which ill be in at the hottest 94 towards the ned of the trip

[datzenmike]

 

Mine ran just above 1/2. Maybe a needle width below yours but just barely noticeable that it was above 1/2. 

[datzenmike]

Find out what Nissan recommended for initial or static timing. Otherwise crank it up to 12 like all other L series like the L20Bs. If it pings under full throttle back it off in small amounts till it just stops. Timing that is too low throws away power and mileage. It also completes the combustion process going out past the exhaust valve and that heats up the exhaust port, and that dumps heat into the cooling system.

[ggzilla]

According to Datsun owner's manual: "the engine will run satisfactorily when the pointer is at any position in the middle range." However, if the temperature is smack in the middle in winter, and only goes higher on hot days, it means the cooling system is not keeping up. The factory radiator was just big enough when new. The A/C equipped rigs had a bigger radiator. Better to fix it when you have a chance (with a bigger radiator), it will only get worse

7 hours ago, Chance said:

whats a normal range for the gauge to be in mine gets to like 75% then stays there.

 

[NC85ST]

Is this truck fairly new to you? The only way to really know what the engine temp is, is to have a mechanical gauge. If the temp stays where you’re showing, even when pulling a hill, I wouldn’t worry about it. If it starts going up every time you’re putting more of a load on the engine, then you need to think about upgrading the cooling system. You’re brave to drive that truck in a 110 degree heat. I wouldn’t even leave the house.

[datzenmike]

 

This is fine. If 110 out, then it's expected to be slightly higher.

 

If the cooling system is working you should be able to drive in 110 heat. An infra red hand gun will also lay it what the temperature really is when idling. Just 'shoot' the thermostat cover. However in extreme heat I would pay more attention to the cooling system, same as in extreme cold. Anything wrong, fix right away.

 

Always run 50/50 distilled water and anti freeze.

 

Fan belt tensioned and inspect for damage

 

Fan shroud ON the vehicle. It increases fan efficiency.

 

Radiator clear of obstructions to air flow. Also inspect the inside for 'kettle scale'. Not a problem if you use distilled water.

 

Inspect hoses and clamps. Look for soft hoses. Hoses rot out from the inside our, look fine on outside.

 

Buy the special rad cap and install a coolant recovery bottle. Wrecking yards are full of these containers that might fit your truck. Collects any coolant expelled in the heat and when cooling down it returns it to the cooling system.

 

Inspect the clutch fan for excessive slip. More slip = less air through the radiator.

[banzai510(hainz)]

On 8/8/2025 at 9:56 AM, NC85ST said:

If you’re still having the issue described in the beginning, running hot, leave the truck at home and drive something else.

Exactly!!!!!!!!!!!

 

to me the distributor should be able to go from Zero to 25BTDC in the timing slot using the timing light.  If this truck is new to you I would put motor on TDC and pull the dist and look at the drive.

 

I would regulate this older rigs to local only myself  after 85 my 521 and 510 gets HOT and they have 3 core rads. In traffic it gets HOTTER. Driinvg its fine.

 

I would NOT drive this.

 

 

put on TDC and take a photo and show us.

Edited August 9, 2025 by banzai510(hainz)

[datzenmike]

16 minutes ago, banzai510(hainz) said:

... I would put motor on TDC and pull the dist and look at the drive.

 

Remove the two 10mm? bolts securing the distributor to the timing cover, and the ignition timing will not be disturbed when you put it back.  You should see this orientation with the distributor out:

 

 

If not exactly this, the drive spindle (screwdriver blade thing) has to be dropped out and moved a tooth. See what you get first. 

[Chance]

I made it, stopped to have it cool down a bit once in awhile and then it would get immediately hot when I turned it on and not go. turns out the choke plates were getting stuck and wouldn't open. so I took the choke plates out and it got me the rest of the way there. I think the electric choke was having issues opening up all the way.

[banzai510(hainz)]

i would just cranked the choke adj all to one side to keep it open then disconnect the 12v choke wire. So your sayn having choke on is causing over heating? I can see not going over 45mph choking off the high end

[ggzilla]

Is this a Weber carburetor? Cause factory carb has only one choke plate

 

Sticking choke would make it run poorly. Might be able to adjust the idle mixture to compensate, but anything above idle will be running rich

[datzenmike]

21 hours ago, Chance said:

I made it, stopped to have it cool down a bit once in awhile and then it would get immediately hot when I turned it on and not go. turns out the choke plates were getting stuck and wouldn't open. so I took the choke plates out and it got me the rest of the way there. I think the electric choke was having issues opening up all the way.

 

Immediately hot after turning on shortly after shut down is totally normal. This is called heat soak. Fan and water pump are not turning and heat produced just before being turned off hasn't escaped yet. 

 

I've has the electric choke wire fall off and the choke still opens, not fully, but just the under hood temperatures are enough to move the choke flap. If actually sticking find it and fix. Running rich would run very slightly cooler I would think. Heat is removed evaporating the excess gas that is not used.

 

 

Did you ever get an infra red gun and shoot the thermostat cover to see what the actual temperature is and not the gauge. Everything is based on you gauge.