Cooling an L20B in a '73 620

[Tony620]

Now that I've got my wiring at a minimal safe operating standard, I'm moving on to the cooling system.  I'm planning to disconnect and flush 1) the Heater Core, 2) the Block, and 3) the Radiator.  I'm happy using the clutch fan I have on there now but i have no shroud and eventually think I want an electric puller fan.  Anybody have an opinion on finding a fan shroud?  My radiator isn't stock, though.  I think it's OE from a Z car and needs to be mounted proper; it's presently right against the battery.  I'm inclined to get a new radiator that better fits the space but that will have to wait until after I've tackled other engine issues.  Any good advice on what NOT to do when flushing these components?  I've read here some good tips like distilled water and such.  I'm a little nervous because round about 1998 I killed a Z24 720 by flushing the Radiator and putting on a brand new fancy radiator cap.  Driving it 40 miles home two nights later it overheated on the highway, the wall of the radiator had split open, and by the time I got it parked the head was too warped to save it.  To this day I'm convinced I caused a disturbance in the force trying to do "the right thing" by flushing my filthy orange soupy radiator fluid.  Like I weakened the walls or created a hot spot (air bubble?) somewhere critical.  Maybe dislodged something which later blocked something, etc.  Anyway, would hate to kill this engine with kindness so early in our relationship.  Thanks,

[Tony620]

Oh yeah, I read here about how the cast fins in the water pump are the ones to get, not the aftermarket bent steel ones.  So I saw Amazon had one with the cast fins and ordered it.  Well, I'm in the process of returning it now because it arrived with the bent steel fins, despite the picture in the listing.  

Here's the image from the listing:

 

Here's my picture from the received part:

 

Beware.

[datzenmike]

Distilled water is a preventative. It does not contain any dissolved minerals that collect, concentrate and clog the radiator fins. It's the same as calcium scale on the inside of an electric kettle.

Always use a 50/50 antifreeze coolant mix. It contains anti rust ingredients to prevent that orange soup..

Get a coolant recovery reservoir and the special rad cap for it. The coolant recovery will collect any coolant expelled from the rad and when it cools down it will siphon back keeping it topped up. Automatically. They are pure genius.

You have a heat gauge use it. No engine boils over so fast you can't pull over and save the head. You can even turn the heater on for some slight increase in cooling.

 

 

There's no way for a bubble to be inside the engine. It would travel up into the head which is tilted up at the front. It would work it's way to the thermostat and burp out into the rad top tank.

[EDM620]

5 hours ago, Tony620 said:

the cast fins in the water pump are the ones to get,

The cast fins have much more surface area than the bent steel ones plus are curved, overall producing much better flow.

[DanielC]

On this page of one of my 521 threads, I show how I flushed the cooling system.

https://ratsun.net/topic/49698-my-dragon-datsun-521/page/13/

As for your option of a fan shroud, try to find a stock radiator and fan shroud in a junkyard.

[datzenmike]

Sharp edges tend to cavitate more when spinning at high speed. And the L16 is a revver.

 

Causes of over heating are

 

lack of air

Missing shroud

Rad outer fins bent, damaged or plugged with debris.

Fog lights, bush bar or license plate blocking flow.

Belly pan missing. (cars usually have them)

Fan damaged

Wrong size rad.

 

or lack of coolant flow.

Soft lower rad hose collapses at high speed from pump suction.

Rad core blocked by hard water scale

Belt loose and slips at higher speeds.

 

Also ran...

Heater hoses looped together

Head gasket going.

Ignition too retarded.

 

 

[Stoffregen Motorsports]

There's the old adage, if it ain't broke, don't fix it. Why do you think you need to boil out the block? If you think there is crap in the block, the best way to flush it is to remove the freeze plugs (core plugs, Mike) and make sure all the junk gets out. You can even just remove one or two.

 

If the engine is out, and you suspect there is junk in the block, remove the plugs and clean it that way. If the engine is in the truck, and you just want to be proactive, maybe just flush it with a hose and call it good.

 

Mechanical clutch fans pull more air than similarly sized electric fans. Leave the mechanical fan if cooling is your goal. If you have some fab skills, you can get an electric fan to work better by building a shroud for it. The best electric fans will cover as much of the core as possible.

 

If you're interested in proper electric fan sizing, go to https://www.becool.com/products/category/electric-fan. Somewhere in their website is a tech page with all the motor sizes with hp and amp draw. It can be very helpful.

 

...and get a proper radiator that fits.

[wayno]

Personally I would look for the latest model 620 radiator/shroud that will bolt into your 73 620.

[datzenmike]

The 620 did come with a 3 core for the L20B. Even a 2 core '75 and up L20B would be better. If it overheats with one of those you have a problem other than the rad.

[banzai510(hainz)]

Get the Japan made ones.

Cast ones are better but I have run both.  But never the newer China made ones. if its under 20 bucks you can figure it out where its made and the quality.

 

Aisin(Japan)  makes them if one can find them

 

Atsugi was the main producer

 

buy the 50/50 mix at Walmart. Supertech or Prestone is fine

Edited August 22, 2020 by banzai510(hainz)

[Tony620]

You guys are awesome!  So helpful.  Much appreciated.  Used my garden hose tonight to flush the Radiator, the Heater Core, and the Engine until the water ran clear.  Removed the radiator, disconnected the heater hoses, the bypass hose, but didn't remove the thermostat or housing.  I'm lazy (cheap?) and didn't want to have to redo the gasket if not needed.  I have new radiator hoses already.  Getting new Heater and Bypass hoses 'cause they're brittle.  Also changing the oil while I'm at it but that's a whole nuther thread...  Hope to make some progress this week.  Will post photos to show my appreciation.

[datzenmike]

A word on your oil choice. Our Datsuns were built when the zinc anti scuff additive ZDDP was around 1,200 PPM. Today's cars don't need it as much and it buggers the catalytic converters so oil maker have been lowering it down to around 600-700 PPM and though they say today's oils are reverse compatible and safe to use in out old cars I don't believe it and take no chances. It's as easy as reaching for a diesel oil as they have the original levels. I use Shell Rotella T4 10w30 or 15w40 but there are others equally as good. NEVER use a fram filter. Use NAPA Gold or WIX they are still good and always change the filter any time you change the oil.

[Tony620]

19 hours ago, datzenmike said:

A word on your oil choice. Our Datsuns were built when the zinc anti scuff additive ZDDP was around 1,200 PPM. Today's cars don't need it as much and it buggers the catalytic converters so oil maker have been lowering it down to around 600-700 PPM and though they say today's oils are reverse compatible and safe to use in out old cars I don't believe it and take no chances. It's as easy as reaching for a diesel oil as they have the original levels. I use Shell Rotella T4 10w30 or 15w40 but there are others equally as good. NEVER use a fram filter. Use NAPA Gold or WIX they are still good and always change the filter any time you change the oil.

Maybe kinda related (older engines, newer fluids) is the topic of Ethanol Blended Gasoline...  Any opinions there?  Are L series particularly at risk from higher levels of Ethanol mandated in USA gasolines nowadays?  I do have the option of buying Ethanol free gasoline, if worth the premium.  Thanks,

[datzenmike]

Been running up to 10% ethanol for 30 years. Runs fine, runs clean. It's hard to a/b ethanol blend and non ethanol. Probably less power but shrug.

[wayno]

If you daily drive your 1973 Datsun 620 you are fine, I drive my 1971 Datsun 521 work truck all the time(at least I used to) and have never had an issue with ethanol gas except when I had dual tanks, if the ethanol gas is always fresh it will not spoil and rust your tank out, it only takes 2 to 4 months for ethanol gas to spoil in a metal tank.

I just got another free lawn mower because they could not get it started, it took a while for me to get it started because the carb bowl didn't have a drain plug, but I got it going, it appears to be a great lawn mower, it just sat 6 months and the ethanol gas spoiled as when I emptied the tank into a container it had 2 separate layers, and the lawn mower would not run on that bottom layer.

 

DMike is an anomaly, gas never spoils on him, he can let mixed gas sit in a can for years and he never has an issue, but he is the KING RAT.

[datzenmike]

It sits in my 710 from the end of summer till spring, or Oct to April no problems. I have a gas trimmer and a gallon of mix lasts 3-5 years and I fill it up every spring 3-5 pulls and away I go. Oct through March is rainy season. Alcohol will absorb some water from the air so a tight fitting cap is probably important. Wayno, maybe Canadian gas is different somehow.

[Tony620]

I did search for this one, I mean it...  Oil Drain Plug seal: Nylon Ribbed or Crush Washers?  I've been very happy with nylon ribbed on my Dodge 318, a Hyundai, a Kia, and a Suburu...  Some folks swear by Copper Crush..   

[EDM620]

IMO the ethanol blend does deteriorate much more than gas without, but it still takes awhile. Gas in my motorcycle that hadn't been ridden for over a year wasn't good, and needed a dose of gasline antifreeze (Methyl Hydrate) to get it to run normal, but the gas in my lawnmower after sitting over the winter is still ok - but does start easier with a dribble of gasline antifreeze added into the tank. The ethanol certainly seems to get gummy in float bowls (& therefore gas lines).

[datzenmike]

I can't see how it deteriorates or 'goes bad'. There's nothing to go wrong with it only that it might absorb water. Alcohol will mix with either but if enough water is added it 'falls' out of the gas and sinks to the bottom of the tank. I don't know anyone up here that has had this happen. I've seen wayno's pictures of separated gas.

[Tony620]

I'm reading here that the ethanol risk isn't unique to Datsun motors. So no special care need be taken beyond any normal coping with ethanol measures already in practice.

 

Here's an article covering ethanol in fuel discussion:

https://www.popularmechanics.com/cars/hybrid-electric/a6244/e15-gasoline-damage-engine/

[datzenmike]

Second sentence says it all. Phase separation caused by moisture infiltration. If you gas separates your gas cap is shit.

[john510]

20 hours ago, Tony620 said:

Maybe kinda related (older engines, newer fluids) is the topic of Ethanol Blended Gasoline...  Any opinions there?  Are L series particularly at risk from higher levels of Ethanol mandated in USA gasolines nowadays?  I do have the option of buying Ethanol free gasoline, if worth the premium.  Thanks,

I would run ethanol free no matter what if i had the option.If you frequently fill the tank with cheaper fuels you're probably fine.Just don't let it sit for long.Google "ethanol in boat engines" and you'll see what problems it creates in severe cases.I only use Chevron fuel in my boat because it sits for long periods of time.Also a little bit of Stabil.Fortunately it has a plastic fuel tank.I'm not sure but i believe your better quality fuels have less ethanol.Phase separation has nothing to do with a gas cap.

Edited August 24, 2020 by john510

[datzenmike]

If water or damp air get in it will.

 

If I drove long distances I might try a few tanks and keep track of the mileage vs. cost. Got to assume the 'real' gas has more power but if the increased mileage doesn't off set the added cost why bother. Would be better on today's EFI that carefully regulate the mixture and timing to extract the most from the fuel used but I'm not re-jetting a carb for this and then have to drive around looking for the fuel I need.

 

Like I said I have never seen gas separate like wanyo's did. Maybe US gas has more dissolved water in it and closer to phase separation. You guys should look into that as you're paying for watered gas.