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Normal for L18 and L20 to run hot?


Mike Phillips

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My last 1978 Datsun 200SX ran hot and now my 1974 Datsun with a L20B seems to run hot just like the 200SX

 

Both vehicles were purchased used and all I've basically done is the basics, tune-up, new gaskets, new hoses, new belts, new thermostats, flush engine and radiator, and then fill with all new fluids etc.

 

Both the car and the truck seem to run hot?

 

Is this normal?

 

Like half way on the gauge to 3/4 on the gauge. I drive the truck 150 miles one way yesterday in cold rainy weather and had to run the heater on full to keep the engine at 3/4 on the gauge, sometimes 1/2

 

Or do I need to,

 

Replace the water pump

Install a new/better radiator

Install an electric fan

 

:confused:

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i asked the same question when i got my 620 to run decent. this may help.

 

http://forum.ratsun.net/showthread.php?t=5859

 

everything in my cooling system is new witht he exception of the rad. it was a used one. the odd thing is now my tems stay well below the 12 way point. no idea why.

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i asked the same question when i got my 620 to run decent. this may help.

 

http://forum.ratsun.net/showthread.php?t=5859

 

everything in my cooling system is new with he exception of the rad. it was a used one. the odd thing is now my tems stay well below the 12 way point. no idea why.

 

Good read, thanks for the link.

 

I'm going to see if NAPA can get me a t-valve for the engine block so I can use the stock temperature sending unit to the idiot gage and then also add a mechanical temperatures gauge.

 

Next, DatsunScott told me he had the Radiator in his 1965 recored by a guy in Santa Ana and he added an extra core. This way everything bolted in just fine. Think I'll look into this. Kind of want to nip this in the bud and forget about it.

 

Will look into the water pump with cast vanes next. Is this something NAPA can get me?

 

What about an electric fan in front of the Radiator? Saw a bunch of small ones on cars while I was traipsing around the local Pick & Pull today.

 

:)

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You have poor cooling if the temp creeps up.

Sounds like you could just be using 192 deg stats. Drop it to 160 or 180 deg. See if it holds at a lower temp. If not, then you just need to replace your radiator. If you've already done a proper flush, that's all you can do.

 

oh, and try to find a radiator fan shroud if you don't have one. Those help at lower speed driving.

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You have poor cooling if the temp creeps up.

Sounds like you could just be using 192 deg stats. Drop it to 160 or 180 deg. See if it holds at a lower temp. If not, then you just need to replace your radiator. If you've already done a proper flush, that's all you can do.

 

oh, and try to find a radiator fan shroud if you don't have one. Those help at lower speed driving.

 

I installed a brand new 180 degree thermostat and a brand new 15 pound radiator cap. Flushed everything added 50/50 pre-mix coolant.

 

Before I installed the tranny and engine I went through and replaced every gasket, hose, belt etc I could so it was pretty sanitary install. While not pictured below I am running the factory shroud with the factory fan and fan clutch.

 

DatsunEngineSwap201.jpg

 

 

Looks like I'm going to remove the radiator and either replace it or have it re-cored.

 

Thanks everyone...

 

:)

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If he was running hot at highway speeds, I don't think a fan will help much. At speed there is more than enough air passing through the rad to do the cooling. If you need a fan running all the time something is wrong. I have a Z24 in my 620 and an electric fan that is not hooked up yet.The temp runs in the 1/3 range and creeps up only at extended stops. My Sundance has only an electric fan and it never comes on even at lights. You would have to idle for 5 minutes for that.

 

That's an L20B in that truck. If the rad is for the original motor, then it is sized smaller and for an L16 or L18. When L20B were added, Nissan re designed the rad support for a deeper presumably wider rad.

 

http://i138.photobucket.com/albums/q251/datzenmike/truckradsupportL20b.jpg[/img]"]truckradsupportL20b.jpg

 

Use the L20B rad, if you do have one, get the 3 core. (most are)

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Check your ignition timing first. If it is retarded, it will cause your engine to run hot.

 

Thank you wise one...

 

Somewhere on this forum I posted about not being able to find my timing tab after I removed it to clean up the engine and paint it. When I got the engine running I just guessed at the timing. :eek:

 

Since then I found the timing tab but have not bolted it on and re-checked the timing. I'm removing the alternator to take it to NAPA to try to match up to a new Saturn alternator and when I do that I'll bolt the timing tab back on and check the timing and hopefully that's at least part of the problem although the engine seems to run very well where the timing is currently at. Drove it on a 300 mile trip yesterday and while there was a few glitches it did seem to run really good.

 

If

Use the L20B rad, if you do have one, get the 3 core. (most are)

 

Good insight...

 

Yep, the truck came with an L18

 

There's a 78 I think in one local P&P and a 3-4 Datsun trucks in the other P&P

 

What year did they start putting the L20 into the truck? Or what years trucks would have a compatible radiator? I can fabricate enough bracketry to install whatever. Guess I'll go out the the one P&P tomorrow morning and see what they have that looks good.

 

Thanks for the good insights...

 

:)

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The Z22 rad he has, has the top hose on the wrong side but.... It's also wider than an L20B so not sure how it will fit the old style support. The same rad but with the left side upper hose was used in the '79 200sx. (I had one in my 620)

 

Mike if you go for the L20B rad try for a three core one, just look in the rad cap.

 

Who's Denmark?????

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Check your ignition timing first. If it is retarded, it will cause your engine to run hot.

 

Checked the timing tonight, it was at 20 degrees before TDC

 

I set it to about 11 degrees TDC with the vacuum line off and plugged.

 

:)

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Local Pick-A-Part has a 1978 Datsun with a core support that looks like this,

 

truckradsupportL20b.jpg

 

The radiator looks good, as in clean not all beat up and even newer looking as in it might be a newer replacement.

 

I'm guessing this will bolt into my original holes but now the fan will be closer to the fins of the core?

 

:confused:

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Having your timing set at 20 degrees sound a little funny to me. I would think a more or less stock L-engine would knock quite a bit with that much timing advance.

The idea of checking the coolant temperature with a meat thermometer sounds like a good one, check the meat thermometer first to confirm it is good.

With my Datsun pickups that I have towed horse trailers with, I needed a 90 degree day, two horses, and climbing a 6 percent grade to make the engine run hot enough to require turning the heater on to keep the temp close to normal, if the engine is in reasonably good shape. In the winter, I would often block off a lot of the radiator with a piece of cardboard to allow the truck to warm up quicker.

Is your timing pointer accurate? As old as our Datsuns are, there is a possibility a previous owner has swapped timing chain covers, timing pointers, or crankshaft pulleys.

If your timing is actually retarded, it causes the engine to run hotter because more of the cylinder walls are exposed to the burning gasses, and they just heat up the coolant, instead of the energy being used to push the piston down. Too advanced timing causes the pressure to build up too soon and that tries to push the piston backwards, and the engine usually knocks.

How is the compression on the engine? If the piston rings are worn, more hot gasses blow by the piston, and that can cause the engine to run hotter.

It has been said before, confirm that the temp gauge is accurate. If it is, and your engine is really running hot, then look for cooling system problems, but also remember engines that are not running efficiently will strain the cooling system more. Even though gas is cheaper right now, you really want to use the gasoline to move your Datsun down the road, instead of heating up your coolant.

Edited by DanielC
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The only time I have seen motors run consistently hot is when the timing was retarded.

I don't mean the initial or idle speed timing, but full timing which should be around 35deg at 3000 rpm. About half the advance comes from the dist. mech. advance weights and half from the vacuum can (around 11deg. each). The advance weights can become gummy over time and the vacuum can diaphragm will rot away from fuel contact.

 

The actual timing specs can be found in the down-loadable PDF 620 factory service manual.

Edited by hogboy52
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