Overheating after modifications, what am I overlooking?

[jeremy93ls]

My 78 is getting too hot.

I've done a few things to it since it was on the road, so keep in mind that I'm unable to drive it right now, only idle it when backed out of my basement garage.

Here's what's been done to it since I drove it a few years ago that relate to the cooling system:

-Deleted the coolant bypass line just to tidy up the engine bay. I plugged the thermostat housing and plugged the small coolant line that comes off the heater hose hard line by the #1 spark plug.

-Tested the 180* thermostat in boiling water and drilled out the tiny bypass hole in the thermostat just a wee bit after reading about others who had bypassed the coolant line attached to the manifold.

-Pulled the radiator out, flushed the not-so-cruddy mixture out of it, then poured in a gallon of water with a measured bit of muratic acid and shook/rotated/flipped/worked the mixture throughout the radiator to hopefully clean the passages. After a few minutes, I emptied, rinsed like mad and stuck it back in the car and filled with coolant/water mix. It's as full as it can get without lifting the front of the car and topping the radiator off. No air pockets, as far as I can tell. I ran the heater a few times to circulate it through the heater core and squeezed the hoses while topping it off. New Sankei radiator cap.

-Replaced the aged water pump with a new Asin water pump with the cast propeller, and not the thin blade propeller found in some cheaper aftermarket units.

Now, all of that above was done before I realized any overheating problems. I figured most of this was good practice on an old car and it makes me a little less nervous about a long trip with the wife with me if certain parts are replaced. I don't want to swap a water pump in a parking lot somewhere.

This car always seems to take quite a while to warm up. (been that way since I bought it 4 years ago from original owner who did not tinker with it at all) Anyway, as it idles and (very) slowly reaches operating temp, the gauge continues to rise. Before I parked it in the basement a few years ago, it would barely get past the middle on the temp gauge in hot weather. Now, idling, it gets to 3/4+ before I shut it off, open the hood and let it cool down. Something I've done has affected it. Today when I shut it off at the 3/4 point, there was a bubbling sound coming from the thermostat housing and the coolant overflow was at the lower level line. I don't think I've ever seen the coolant overflow bottle with any coolant in it since I've had it.

I thought I read enough from others who deleted those coolant bypass lines with no problems, but maybe that's causing this to happen. Or, did I unclog something in the radiator with the acid /water flush?

 

 

[Zed Head]

1 hour ago, jeremy93ls said:

-Tested the 180* thermostat in boiling water and drilled out the tiny bypass hole in the thermostat just a wee bit after reading about others who had bypassed the coolant line attached to the manifold.

I'd get a new Nissan thermostat from your Nissan dealer (I got one a few years ago, I think that they're still available) and install it as-received, no holes drilled.  It's the most unknown of your unknowns. The boiling test doesn't really tell you  much except that it opens at 212 degrees. 

[siteunseen]

With the motor off see how easy the fan turns by hand. A good fan clutch should barely if at all make one complete rotation. If it spins easy you may need a new one. $20 at Advance maybe less with a coupon code from retailmenot.com, usually 25 to 30 percent off buying online and pick up at the store.

Can't beat a Nissan thermostat like Zed says. Not even those Super Stants.

[jeremy93ls]

Fan clutch spins with resistance, as it should. I replaced it a few years/hundred miles ago. That is a good idea, though. When mine failed, it sounded like a tornado when I accelerated.

I'll pick up a new thermostat next week at the new dealership near my office.

[jeremy93ls]

19 minutes ago, siteunseen said:

With the motor off see how easy the fan turns by hand. A good fan clutch should barely if at all make one complete rotation. If it spins easy you may need a new one. $20 at Advance maybe less with a coupon code from retailmenot.com, usually 25 to 30 percent off buying online and pick up at the store.

Can't beat a Nissan thermostat like Zed says. Not even those Super Stants.

I like how you made sure to say "with the motor off" haha

[Zed Head]

23 minutes ago, jeremy93ls said:

Fan clutch spins with resistance, as it should. I replaced it a few years/hundred miles ago. That is a good idea, though. When mine failed, it sounded like a tornado when I accelerated.

I'll pick up a new thermostat next week at the new dealership near my office.

A new dealership might have to order it.  And if they have new parts guys you might have to give them the part number.  Or you can get it from Courtesy Nissan.

It's been superceded a few times.

http://www.carpartsmanual.com/datsun/Z-1969-1978/engine-280z/cylinder-head/41

https://www.courtesyparts.com/?p=catalog&mode=search&search_in=all&search_str=21200-V0100

[Diseazd]

I would look at your fan clutch like Site suggested. I put a brand new one in my new Stroker motor. The engine ran cool when moving, but at a stop light or idling, she would over heat. I replaced it with an old one and it solved the problem. She now idles dead center.

[sweatybetty]

the small hole in the thermostat helps to bleed the air out of the system when the stat is cold/closed. a 1/8" hole in it does the job just fine

[jeremy93ls]

I swapped out the thermostat with a Nissan 180* this morning, but it didn't make a difference. $24 shipped because I'm lazy.

The fan clutch won't even make a full rotation if I try to spin it. I've dealt with a bad one before, so I'm confident it's not the problem this time.

On a related note, that Permatex 'Right Stuff' is an awesome product for gaskets. Buy some of this if you don't have it already.

 

[Chickenman]

Here's a thought. Have you actually measured the water Temp in the radiator with a Temperature probe? Could be a faulty gauge, sensor or even a bad ground.  You can go to your local Parts supplier and get one of those Radiator temp testers for very cheap.  I use a digital  Candy/Meat thermometer that can immersed in liquids. $15. 

[Chickenman]

The other thing is that Coolant reservoir. It should be a minimum of 1/2 full when cold. You may have an air lock in the system.  Can happen after a fresh fill of Coolant if proper procedures aren't followed. 

After installing fresh coolant.

1: Make sure the coolant reservoir is  at least half full. Warm the engine up fully with the rad cap removed. Have the heater valve turned to full hot.  Fan must be on with Auto Climate control. Watch the water level. When the stat opens the fluid level  should drop. 

2: Add coolant as necessary. Revv engine  to around 2,000 to 2,500 RPM. Coolant level should drop further. While maintaining Revs , fill the radiator to the absolute Brim with coolant. Quickly install the Rad cap. Reduce revs. The idea of revving the engine is to pressurise the engine block and head and eliminate any Voids where air can be trapped. It will also ensure that the coolant recovery bottle pulls a  solid siphon when you shut the engine off.  

 

You can repeat the above procedures if you think you have an air lock. Might be a good idea.  

[jeremy93ls]

2 hours ago, Chickenman said:

1: Make sure the coolant reservoir is  at least half full. Warm the engine up fully with the rad cap removed. Have the heater valve turned to full hot.  Fan must be on with Auto Climate control. Watch the water level. When the stat opens the fluid level  should drop. 

I got this far, but as the thermostat opened, coolant started gushing out of the radiator. Temperature gauge was a little over halfway. This video was from immediately after shutting it off. This went on for a few minutes. The overflow reservoir never dropped. Before the thermostat opened, the coolant level kept rising up and out of the radiator, too.

 

 

VID_20171028_132300927.mp4

Edited October 28, 2017 by jeremy93ls
embedded youtube video