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[Datsun 1200 encyclopedia]


From Datsun 1200 Club

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Category: Cooling System

Datsun 1200 uses a traditional pellet-type engine cooling thermostat. It regulates temperature by closing when cold to keep hot water in the engine, and opening when hot allowing the coolant to flow to the Radiator.



15157.jpgAlbum 15157

Datsun factory options were:

  • THERMOSTAT 170 F (75.5c optional, for tropical use)
  • THERMOSTAT 180 F (82 c, for standard use)
  • THERMOSTAT 190 C (88 c, optional for winter)

The thermostat regulates coolant flow from the engine to the radiator. When the engine is cold, the thermostat is closed, allowing no coolant flow to the radiator. So you engine warms up relatively quickly (5-10 minutes). As the temp rises the thermostat gradually opens and when it has exceeding the rated temp it is fully open. The coolant is therefore allowed to flow outwards and be cooled in the radiator. It is cools too much, the thermostat closed up again. In this way the temperature of the engine is regulated to within a few degrees of the rating.m

Note that this will not regulate the radiator temp, but only the engine temp, which is usually measure at the cylinder head coolant passages. So how does the radiator avoid overheating? Primarily by the manufacture choosing a large enough radiator such that the maximum power output never produces more heat than the radiator can handle.

Cooling Thermostat


Replacement of the thermostat is called for when:

  1. Put a bucket under the radiator fan to catch spilled coolant
  2. Loosen the clamp on the hose at the water outlet
  3. Twist and pull the hose off the outlet
  4. Remove the two fastening bolts
  5. Scrape all traces of gasket off water outlet and cylinder head face
    • be careful not to nick the aluminum of the gasket faces
  6. Fit thermostat into engine, then gasket, then housing and tighten moderately
    The gasket goes against the housing (not the head).
  7. Top up coolant
  8. Rinse spilled coolant off engine and body with water
  9. After engine has been fully warmed up, and cooled down, top up coolant again.
Be sure to fit thermostat with spring facing into engine

WARNING: Due to air pockets, the coolant level usually drops down and the engine can easily overheat if not monitored for a few days after changing the thermostat.


It is not unusual with any 10-year old stock radiator for the temperature to rise during summer. If this occurs with your Datsun, don't panic. The engine can run all day close to the "H" mark.

DO NOT let it go onto the H mark. Pull over immediately if it goes past the H mark. Don't wait 30 seconds, it could be too late.

Typical Temperature
If this worries you, fit a slightly larger radiator to provide more cooling than Datsun provided with the 1200s.

According to Owner's Manual: Water Temperature Gauge,
the engine will run "satisfactorily" in this range:

1972 USA Owners manual (Page 10 ... ):

29357.jpg   29362.jpg
For most types of driving, the pointer will hover about halfway. However, the engine will run satisfactorily when the pointer is at any position in the middle range.

TIP: Use the stock engine-drive fan. Electric fans are notorious for failing to cool the radiator in stop/go traffic. Of course an electric fan can work well, but many don't.

What is the correct temperature the engine should run at?
Primarily, this depends on the thermostat. The engine can run fine at a variety of temperatures. You can get different temp thermostats, and the coolant should stay steady at that temperature.

Datsun factory options were:

* THERMOSTAT 170 F (75.5c optional, for tropical use)
* THERMOSTAT 180 F (82 c, for standard use)
* THERMOSTAT 190 C (88 c, optional for winter) 

These three thermostats were mainly because of the heater. 170 for hot climes so the room heater won't put out much heat, 190 for cold climes so the heater puts out more heat.

180 is recommended for all street cars, it will keep the oil at optimum temperature (oil runs about 20 degrees hotter than the coolant). A guy at the oil company told me 180 is ideal for the oil working the best. He went through training for Mobile I think it was and they were formulating oil for 200 degrees, which works out to be 20 degrees warmer than the coolant for most engines. Maybe it's changed now but it won't be colder as engines now run hotter than ever. If anyone has documentation for this please add it here.

160-degree is favored by some for drag racing as they tune the carbs for cold dense air, or for use with low octane fuel. But EFI computers don't run well at cold temps nor does the oil, and cold temps mean more engine wear. Cold temps are not recommended.

But won't I make more HP with a colder thermostat?
Not if your carburetor jetting is stock -- it expects warmer less dense air. And when you floor the accelerator pedal, the air cleaner hot air duct opens up letting only cooler air in, and the stock Hitachi compensates via the power valve. Those clever Datsun engineers had it covered.

Many cars use a 195 F degree thermostat along with a 14 lb. radiator cap to raise the boiling point. A radiator is more efficient at higher temperatures, because the temperature differential to the air will be greater, thus shedding heat faster. In turn airflow can be reduced which increases aerodynamics.

After the thermostat, the radiator is the next factor. If your temp. stays steady except on hot summer days (which is normal), you can use a bit larger replacement radiator and it will stay steady even during temperature peaks. Use either a new unit, rebuilt unit, or a good used unit from a B210 or B310, which are larger than the 1200 radiator.

See Radiator.

Thermostat Types

Newer Type -- advanced type with 'jiggle' valve. The jiggle valve is used to "shorten the warm up period" (Nissan Service Bulletin No. 188 Introduction of New Datsun B210, 1973).


The 1969 L16 service bulletin says: "fitted with a jiggle valve to improve defrosting performance"

Thermostat Testing

Test it in a pot of water, heated on the stove, with a cooking thermometer.

  • Notice at what temperature the thermostat opens
  • Check that it opens at least 8mm by using a 8mm-wide screwdriver


Thermostat Part Numbers

Cooling Thermostat. $7-$16

Nissan Part Numbers for B10/B110/B210/B310
180F (82C) 21200-P7901 $19 USD
190F (88C) 21200-P7906 $19 USD (optional, winter)

Buy at


There are many slight variations from different manufacturers:

Another variation


There are various gaskets.

NOTE: 4-bolt gaskets work on a 2-bolt housings.

2-bolt: 11062-18000 GASKET-WATER OUTLET
3-bolt: 11062-M3001 GASKET-WATER OUTLET
4-bolt: 11062-H7201 GASKET-WATER OUTLET
CORTECO 111451
Fel-Pro 352981
Victor Reinz C20116
Gates 33644 
Stant 25168
Stant 25113 universal gasket
Gates 33646 universal gasket

Fel-Pro 25608
Victor Reinz C26075 


For standard B110 180-degree thermostat:
* STANT 13858 with jiggle pin 180 degree (82C)
* STANT 32118 with jiggle pin 180 degree (82C)
* STANT SuperStat 45858 with jiggle pin
* GATES 33478 with jiggle pin
* GATES 33478S Premium with jiggle pin
* BECK/ARNLEY 1430685 
* BECK/ARNLEY 1435685 Fail-Safe
* MOTORAD 2041180
* MOTORAD 7241180 Fail-Safe
* Prestone 391-180
* Prestone 752-180
* ACDELCO 12T25D (19114482)
* ACDELCO 12TP10D {#19114402}
* GATES 33478
* GATES 33478S Superstat
* STANT 45858 Superstat 
* 2 1/8" diameter
* 29/32" high hot side x 13/16" high cold side
Stant 13858

192 degree (use in cold climates)
* STANT 13859 with Jiggle Pin
* STANT 45859 Superstat 
* GATES 33479 with Jiggle Pin
* GATES 33479S Superstat
* BECK/ARNLEY 1430686
160 degree (use in hot climates)
* BECK/ARNLEY 1430684 
* MOTORAD 241160

Honda 1994-1996 PASSPORT
ISUZU 1989-1994 AMIGO, 1992 IMPULSE,
      1981 I-MARK, 1981-1995 PICKUP,
      1985-1989 I-MARK, 1991-1997 RODEO,
      1988-1990 IMPULSE, 1984-1991 TROOPER 
1971-1973 1200
1974-1978 B210
1979-1982 210
1974 260Z
1975-1978 280Z
1979-1982 280ZX
1971-1972 521 Pickup
1972-1979 620 Pickup
1980-1986 720 PICKUP 
1986-1989 D21 Pickup
1987 Pathfinder
1976-1978 F10
1979-1982 310
1983 Pulsar
1983-1989 Pulsar NX
1971-1973 Datsun 510
1973-1976 610
1974-1977 710
1978-1981 510
1977-1988 200SX 
1977-1981 810
1982-1984 Maxima
1982-1988 Sentra
1982-1989 Stanza
1987-1988 Van

Thermostat Housing

Nissan calls the thermostat housing the "Water Outlet".

See Main Article: Thermostat Housing

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This page has been accessed 46,512 times. This page was last modified 23:28, 31 May 2019. Content is available under Datsun 1200 Club.