overheating! 79 620 help!

[Tomeegun222]

my 79 datsun 620 is overheating and isk why ive replace the cap thermostat and coolant but it seems to only do it if i drive my truck over 55mph

water pump? somebody help me figure this out!

oh p.s. me and my dad did a head gasket job on it and maybe we made a mistake?

[Eagle_Adam]

have you tested the gauge and have you replaced the temp sending unit?

[Tristin]

You said you replaced he coolant... did you do a full flush of the radiator? You might have a blockage somewhere thats preventing adequate circulation. Also, as suggested you should check to see if the gauge is faulty; use a temp gun to get a reading and compare it to the gauges reading.

[Eagle_Adam]

easier to ground out the gauge and make sure it goes all the way hot, ur just trying to make sure it fully functions after that i would replace the temp sender

[Tomeegun222]

the sending unit and gauge are fine cause if i pop the hood the coolant is boiling so it IS getting hot but im just hoping its the water pump not a new radiator

also the heater core is not hooked up if that even matters yes i did a system flush

[datsunaholic]

Could be timing. Could be a plugged radiator. Radiators eventually plug up due to corrosion, and use of "stop leak" type products makes this worse. Water pumps usually fail by losing the seal or bearings, not by losing circulation.

[Draker]

Block tester and check for head gasket issues.. Check the radiator for cold spots with your hand (When it's not boiling), ensure you've got all the air out of the system.

[datzenmike]

Check that the fan belt is tight or not glazed and slipping under load.

 

Look at the front of the rad for bugs, leaves, mud and maybe even a plastic shopping gag stuck to it.

 

Check ignition timing. Retarded timing will cause the fuel/air to still be burning as it passes out of the combustion chamber. The coolant around the exhaust ports will have to absorb it..

 

Carefully watch the bottom rad hose while your dad revvs the motor. This is the suction side of the pump and the hose will collapse if rubber is too soft. Maybe the hose collapses at 50 MPH? This could be made worse by a plugged rad core as well.

 

Partly drain the rad and remove cap and look at the vertical tubes. Are they crusty with lime / calcium deposits? If so remove the rad and replace the cap. Lay with the rad hose openings UP. Add a bottle (or two) of CLR to dissolve the calcium deposits and let soak overnight. Or buy a commercial rad flush liquid from an auto parts store. Rinse thoroughly with garden hose.!

[Tomeegun222]

okay so check for my head gasket leaking? im pretty sure my timing is good. TOUCH the radiator when warm to look for air spots?

[Tomeegun222]

_{it actually has an electric fan conversion, it was doing this before the conversion too though}

[elmerfudpucker]

Thermostat?

[Tomeegun222]

it has a new thermostat

[datzenmike]

Don that's another possibility I didn't think of. Tomeegun just instal a new one. They're cheap and you will have a spare if it isn't that. Forget testing... too much time and bother, and it's likely opening anyway or it would overheat at idle.

 

 

_{it actually has an electric fan conversion, it was doing this before the conversion too though}

 

This will sound odd but check that the fan is pushing air through the rad in the correct direction. From outside to inside

[Tomeegun222]

okay so what im gonna do is buy everything to do with the cooling system thermo and gasket,hoses drain plug is leaking too its kinda stripped, and if it all works out then good if not start looking at head gasket

[datsunaholic]

You're going to throw a lot of parts at this unless you fix the actual problem, which I have a 80% certainty is your radiator is plugged or at least badly coated with scale. I give 10% it's a collapsing hose. 10% for something else.

 

Here's why I rule the other things out:

 

1) Airbound: Would show up at idle.

2) Head Gasket: Would show water loss, then COLD temperature at the radiator (due to lack of coolant) which goes instant-hot when you open the cap to relieve pressure.

3) Thermostat: Would show up at idle

4) Fan: Doesn't do much at high speed, so would be more likely to overheat at idle.

 

 

Which leaves:

 

1) Radiator (a partially plugged radiator flows well enough to cool at low load conditions but gets progressively worse at higher load, like freeway driving).

2) Collapsing hose, which would collapse when the engine is turning the fastest (pulling the greatest suction, BUT this could be compounded by a clogged radiator)

3) Timing. Too far either way will cause overheating, but retarded timing REALLY makes it run hot. Sometimes the timing is retarded too far to stop pinging caused by running too low octane fuel, but then it just runs hotter.

 

 

Being that I've been there, done that I still say it's the radiator. Probably why the head gasket blew in the first place.

 

Now, if you actually have visible leaks then fix those first! Low pressure (from leaks) makes it boil easier.

[herculesinwyoming]

i once had a thermostat that was only partially opening, the car would act fine around town, but on the highway it would start to boil over. New thermostat fixed it.

[Tomeegun222]

okay im gonna CLR the fuck out of this radiator and new hoses and stuff wont hurt i got i buddie who works at BAP import parts who gives me manager discount

thanks everybody! you helped me out alot on ideas and datsunaholic you nailed it how my truck is acting.

 

now does andbody know what radiators from other cars will bolt up and work???

[datzenmike]

'75-'79 truck rad will work. There is a 3 core option.

 

 

So did you replace the thermostat yet? Be a shame to pull the rad for nothing. Hell run without it and see if that works. Did you check for a soft lower hose? Rad plugged with bugs or dirt? Electric fan blowing the right direction? You didn't say.

[datsunaholic]

620 radiators are, unfortunately, unique. Any 75-79 will work, but you WANT the '79 3-row radiator. Most aftermarket radiators were 3 row. Of course with enough shadetree engineering you can make pretty much anything fit. Using an electric fan does open up options, but I don't know specifically what else fits the dimensions as I've never had problems finding a radiator when I needed one. Rockauto claims to have 2 in stock (almost $300 though). An old-school radiator shop can rod out the cores, that does involve some disassembly, but they can braize it up and patch any leaks. Some folks never think of that option. Used to be common.

[Tomeegun222]

the raiator doesnt have anything stuck to it i've tried running it wouthout thermostat before it didnt help out but i found an aluminum rad same dimensions but the top hose mount is on the opposite side no big deal. fuck rock auto they are EXPENSIVE hah im on a budget here

[converted_to_datsun]

autozone has a radatior listed at 140 and so does oriley. or pull one from a wrecking yard like i did for 50

[darrel]

620 radiators are, unfortunately, unique. Any 75-79 will work, but you WANT the '79 3-row radiator. Most aftermarket radiators were 3 row. Of course with enough shadetree engineering you can make pretty much anything fit. Using an electric fan does open up options, but I don't know specifically what else fits the dimensions as I've never had problems finding a radiator when I needed one. Rockauto claims to have 2 in stock (almost $300 though). An old-school radiator shop can rod out the cores, that does involve some disassembly, but they can braize it up and patch any leaks. Some folks never think of that option. Used to be common.

 

It's common enough that I did it. $112. The problem, if the rad has a lot of heat cycles the material gets brittle and it will start leaking again.

[Tomeegun222]

gonna take the specs and walk a few junkyards for a day buy all new hoses and thermostat just redo the system should be perfect after that my rad is fucked

[cashi123]

I had the same problem as you before , I replaced the thermostat, waterpump,flush the engine coolant completly, new cap,fan, and it was still doing the same thing but O'reilly hade the radiator for $ 140 so I purchaced and yes it had the top hose on the other side but you can allways get the top hose for a L20 and cut it a little bit and will fit perfect the bottom one is the same and it did stop the overheating problem for good at the end it was the radiator then problem :)

[ryknot]

I would pressure check the system - make sure you dont have a pin hole leak which you can't see. You can rent the stuff to do it at Autozone for like 15 bucks. If its small, the water being pushed through the hole will evaporate before you will see it. Buying a radiator from a wrecking is silly, IMO, you dont know if you are getting anything better than what you got. Before tossing a bunch of money and parts at it continue trouble shooting until you KNOW what youre fixin. No reason to go throwing good money after bad. Again, just my opinion.