620 control arms

[Capt. Koko]

looking for upper and lower control arms with ball joints. Can’t find any for 79, 620.

[datzenmike]

Because control arms don't wear out, they replace the ball joints and/or the bushing connecting it to the frame. For a control arm you'd have to pull one from a '78-'79 truck.

[Capt. Koko]

Thank you Mike… if you don’t mind, I am looking for resolution to known problem in the summer heat here in Las Vegas. I know it is 110° today and heat soak is prevalent and older cars especially since I put ceramic headers in my 79’ 620 l20b.  also has offenhauser intake. The Radiator was flushed and operating nicely, thermostat functioning normally, fan with shroud effective and water pump fine.  Placed a thermal blanket over the headers, but that is not enough. I’m going to wrap them in titanium fabric and change the radiator. Do you have any recommendations on an aluminum radiator that will 1. Fit and 2. accommodate the shroud. I put bigger jets in the Weber carburetor and it’s running like a champ, although I need to have the timing adjusted probably.

my issue is after 15 to 20 minutes it has to cool off to run again.  Is this just a simple matter of not taking it out when it’s 110° out in the desert unless you’re driving Miss Daisy?  

Truck did the same thing prior to me, removing all of the Cali. emissions equipment, including original intake/exhaust that were adjoined.  that carburetor had an eyeglass, and you could actually see the fuel percolate due to the heat last summer.  

[ggzilla]

1. Use the Weber insulating spacer between the manifold and carburetor

2. Install a heat shield between manifold and carburetor, perhaps using the factory one, drilled out for the Weber pattern

3. Make sure your return line is in place and working, as it recirculates the fuel during normal running to prevent vapor lock

 

43 minutes ago, Capt. Koko said:

my issue is after 15 to 20 minutes it has to cool off to run again

[datzenmike]

I don't see the return line. All L20Bs have this to combat high under-hood temperatures. The return allows circulation of cool gas from tank to constantly replace the hot fuel in the lines. 

 

Do you have the stock air filter still (never throw old parts away) you could modify the base to fit the Weber. The stock air filter housing will allow cooler ambient air from in front of the radiator into the carburetor not the 190 degree air under the hood. 

[datzenmike]

 

Can't be sure of intake you have now but the original had coolant flow through both pair of runners and up and out at the base of the stock carburetor and connected to the thermostat by pass. This warms in the winter but also 'cools' in the summer by absorbing radiant heat from the exhaust. Is that the fitting directly below the Weber inlet fitting????

 

 

 

That long fuel line will soak up a lot of heat. Really needs the fuel return line put back on. All L20B used it to prevent heat soaking the fuel. This is the stock return line. It has a small pin hole restriction so the pump can build enough pressure to push into the carburetor. Without the restriction the fuel would simply flow back into the tank. This promotes the circulation of cooler fuel from the tank past the carburetor. Any 'boiling' of the fuel will push bubbles and hot fuel back to the tank.

 

(where possible never use rubber fuel line, use metal. Less chance of a dangerous fuel leak onto a hot engine and ignition system)

 

[Capt. Koko]

Thank You datzenmike and ggzilla  I have decided to return to the original intake and exhaust. Now that I look at them while they are off, the size is not much different and without the Cali. emissions, will look pretty awesome after wire brushing and putting cool looking plugs in place of the no longer needed emission hardware. Datzenmike, You also had a great picture of an intake that you blocked off and put a PCV valve. The Originals have three separate heat shields and will perform much better than my so-called dream set up…. Man those headers are hot. I’ll Also reinstall the fuel return line and place a half inch phenolic insulating spacer.  I think this will be key in combating the conductive heat.  I will treat myself to a headlight funnel with a in-line 3 inch blower fan with ducting going towards air filter. (I just can’t go back to the old air filter). I’ll make something unique and post.   

Edited Monday at 08:38 PM by Capt. Koko

[Capt. Koko]

Luckily, I kept every part I have removed. also, my son and I replaced upper lower ball joints, shocks tension, arm, bushing, and tie rods on Father’s Day. What a gift. The steering is still a little loose, but tolerable. I tightened it up, but I don’t want to go too tight. It feels very connected, but not being power steering. It’s a little more work when turning.

Finally, the direct conducted heat to my current carbureted situation Is likely the source of my heat soak. When I remove the line, there is still fuel in it. I have just taken the mechanical fuel pump out of play and blocked it.  It was very hot and fuel line was dry after last event with it attached. I’m using only the appropriate reduced psi electric fuel pump.  I will still run a return line however I would like to run a return line to the restricted port from the carburetor directly. Is this advisable? and which part would I use. I understand the vent is a top of the 32/36 and the adjacent intake is likely a no go. I really do hope that Phenolic riser will do the job.   

Edited Monday at 08:37 PM by Capt. Koko

[Stoffregen Motorsports]

I'm going to say either bad coil or bad spark module, whatever it's called. Ironically, this is where my years owning older Chevy trucks comes in handy. Whenever a Chevy V8 HEI module starts to go bad, it acts exactly like you describe.

[banzai510(hainz)]

does it run better on a cool NIGHT?

I cant see a manual pump being different as the later trucks had a return line anyways

 

read your post up farther/110? I think it would kill my datsuns  even with a 3 core its still be bad for me. I dont know if the block has so much scaling on the inside. but at temp85 my 510 and 521 the heat rises in stop and go traffic

Edited Monday at 09:21 PM by banzai510(hainz)

[ggzilla]

A 3-row radiator will cool at 120 degrees, unless it has smaller core dimensions than stock. A lot of those eBay aluminum replacement radiators are pretty small

 

Heating up in stop-and-go indicates an airflow problem, and is one reason Datsun started putting fan shrouds on, and later went to electric fans. On the other hand, some aftermarket electric fan setups cool marginally. I replaced a trick electric fan setup with the stock radiator fan and it solved all my stop-and-go cooling problems

 

Another thing that helps is a 205 degree thermostat with a working cap. The hotter the radiator is, the better it sheds heat. You may need to reduce timing 2 degrees when running hotter (but only if the engine pings)

[Capt. Koko]

it definitely is worse when it’s hotter banzai510 also,The coil is brand new.  The cooling system is functioning fine. I did put a 160° thermostat from a 185* to combat the heat. I don’t know if that helped her hurt. Did a cooling system flush and through all of my troubleshooting realize that the Offenhauser intake, which probably isn’t an exact match for my car is a ripping hot chunk of metal well after the header is cool down a little. This is why I’m going back to the original.  I need to bring it somewhere to have the timing adjusted appropriately as I have messed with the distributor without knowing what I’m doing.  when it runs it purrs nicely drives and sounds great till it gets too hot. I did put larger jets in the Weber 3236 carburetor and it ran better.

[Stoffregen Motorsports]

If the coolant temp reaches the point where the engine won't run, that's really bad. We are talking warped head and blown gasket territory.

 

From your description, it really sounds like ignition. Does it have an electronic distributor? If yes, then the module could be on it's way out. If it has points, then it could be a bad condenser.

[ggzilla]

6 hours ago, Capt. Koko said:

I did put a 160° thermostat from a 185* to combat the heat. I don’t know if that helped her hurt.

Well, it didn't help or you wouldn't be asking

 

If the radiator is marginal, all bets are off

 

With a good radiator, at 160, there is only a 50 degree difference from the ambient air temp of 110 summer day. But with a 205 thermostat, there is a 95 degree difference. It will shed heat faster, but only if the radiator is in good shape and hopefully larger/thicker than stock, airflow is good (with stock fan and fan shroud), and the cooling system is working correctly with 15 psi radiator cap

[ggzilla]

5 hours ago, Stoffregen Motorsports said:

From your description, it really sounds like ignition.

 

are you talking about heat making the engine stop running? The 1978 Hitachi electronic ignition is not known to have heat-related problems like the GM HEI has

[ggzilla]

3 minutes ago, ggzilla said:

With a good radiator

 

I should point out that the Datsun 620 radiator -- even when brand new -- was marginal for hot summer days, hence why people put the heater, watch the gauge like a hawk and pray it doesn't overheat

 

Hopefully your 620 has an upgraded radiator, preferably a brass/copper double-row 620 radiator for A/C (larger than the other 620 radiators), or a triple-row aluminum radiator (and a wide one, not one of the little narrow aluminum radiators)

[Capt. Koko]

The heat soak has been a problem since I got it last year. It does run after it cools off and it runs fine. Did a compression test and the cylinders in they’re all even an equal as I said the engine sounds pretty good and when the engine is cool, it idles nicely. There’s no smoke from the exhaust and no leaks. The oil is clean in the coolant to circulating fine. The old line would boil and the carburetor would bubble over and percolate. The new carburetor is bolted directly to the intake so the new riser with the old manifolds and heat shields should take care of a lot of that heat. As I said, I will run the return line and place a new radiator one that is larger. Also, the thermostat I will change to a higher temp. I guess I don’t understand the connection with the ignition or spark, but I will have a professional look at the timing and maybe just go ahead and replace the distributor. But as I said when it’s cool it runs just fine.  

[ggzilla]

I would never replace a part in the off-chance it would fix a problem. They can always be tested. In this case, buy fixing the known problems first

5 minutes ago, Capt. Koko said:

maybe just go ahead and replace the distributor

I think he was talking about heat-related problems with the Chevrolet GM HEI distributor

[Capt. Koko]

Ggzilla. agreed, I will be patient and take this one step at a time, changing the heat related problems to the fuel line to the carburetor first and then reevaluate. Having the carburetor bolted directly to the manifold, which is extremely hot to the touch is obviously a major factor in this. the phenolic riser will help for sure. 

[Stoffregen Motorsports]

13 hours ago, ggzilla said:

 

are you talking about heat making the engine stop running? The 1978 Hitachi electronic ignition is not known to have heat-related problems like the GM HEI has

Yes, that's what I am talking about. 

 

Reading what the OP wrote - that the engine will not run when hot. Like the temp of the engine makes the car actually die and will not start until it cools off - if I take that literally with no interpretation, then there would almost certainly be engine damage. An engine that dies because the coolant it too hot is really bad. 

 

Yes, there could be fuel boiling issues, but that doesn't always make the engine die. It will make the mixture go out of whack, but not usually die.

 

There are many things to try, but all of them are replacing parts in the off chance they will fix the problem.

1 - radiator

2 - heat riser under carb

3 - heat shield under carb

4 - wrap the fuel hoses in a heat sleeve

5 - distributor pickup, which I might add costs only $18 at Rockauto

[datzenmike]

Replace the thermostat with a 180F. 

 

The '75-'77 had the mechanical 'heat rises' in the exhaust that heated the bottom of the intake. All other years flowed coolant out of the head through the intake runners and out to the by pass. Coolant flow through the intake absorbes radiant heat from the close by exhaust. A 180 F intake is far better than a 240F or more one. 

 

Get an L20B metal return line set. This will remove stagnant over heated fuel and promote cooler fuel flow past the carburetor returning hot under hood fuel and any bubbles to the tank. 

[ggzilla]

yes, the stock 1978 620 thermostats

* 180 degrees

* 170 degrees for tropical climate (to keep the cabin cooler)

* 190 degrees for cold climates (to get the cabin warmer)

 

GM liked to run very hot coolant temps so they could fit a small radiator saving $20 bucks on every vehicle. But better than that is a 180 degree system and a larger radiator. 180 is best for the engine and keeps the oil temps at the designed temperature. Anything below 170 will lead to oil dilution because the oil never gets hot enough

 

[Capt. Koko]

we changed the thermostat to a 185. and…., Cracked the thermostat housing where the bolt goes... The lower one with the coolant vacuum and temperature ports.  I see an upper and lower on eBay without the third port from japan so it gives me time to work on everything else till it comes in a week or two. 

[datzenmike]

They are all 2 bolt top until '79 when changed to 3 bolt. All just have the temperature gauge sender but around '73 an opening was added that connected to the by pass line connecting the intake to the lower radiator return fitting that allowed coolant to circulate through the intake runners. This circulation removed the stalled and stagnate coolant around the thermostat and allowed it to open sooner in response to actual internal temperatures during warm up. Later a TVV thermal vacuum valve was added around '74/'75 when EGR was introduced to only allow EGR once the engine warmed up, later vacuum advance was included so there was only vacuum advance once engine was warmed up. On Z cars around '75 a thermal transmitter was added to tell the EFI system if the engine was cold or not. All two bolt top thermostat covers will interchange and work but may have TVV, by-pass and temperature sensors that are not needed. Any unused ports that are open must be plugged. 

 

This is my three bolt top. It will work just as well as the two bolt but you must keep housing and top together. It was on all '79/'83 four and six cylinder L series engines.

 

[ggzilla]

Datsun calls the top the "water outlet" and the piece it bolts to the "thermostat housing"

 

48 WATER OUTLET

36 THERMOSTAT HOUSING

May 1978 may have been a mid-year change

 

the coolant fitting was added in 1972, and there were two sizes of fittings