Overheating (hopefully stupid and simple)

[Eric Corwin]

Hi,

I just bought a '69 Datsun 1600 this weekend (in really good shape). The guy I bought it from said it was running a bit hot and that he thought maybe there was an air pocket in the cooling system. The motor, transmission, etc. are all in top notch condition and I think the guy did a good job with the car. Now for the problem. On the drive home I got stuck in some traffic and the temp gauge went up and up and up until steam came out of the cap of the reservoir tank. I waited for it to cool, refilled with water and got it home. As I pulled into home the car began to boil off water again (from the res. tank). I looked in both the reservoir tank and the small tank on top of the engine. Both were dry.

I read up about it on the internet and tried to refill it by filling the tank on the engine and pushing down on the thermostat. I got plenty of fluid in and was hopeful that this would solve the problem. I think I overflowed the tank on the engine though and when I turned on the car fluid began seeping and sputtering up from the cap on the engine. I then removed some fluid to about 1/2" from the bottom of the tank on the engine and turned the car on. With the cap off for a minute or so the fluid bounced around at about 1" from the top of the chamber and seemed content. However, when I put the cap on fluid again seeped out around the cap. I drove it around the block to see if it might settle down (maybe blow off a bit of extra fluid and then be fine) but it did not. Instead it started steaming from the cap on the engine.

At that point I called it quits for the night and thought I would seek some advice. Does this sound like a problem with the radiator caps (neither seem to be very new) or the rubber washer on the engine cap? Or could it be the thermostat? Or maybe the return line from the engine to the reservoir is clogged?

Please help as I am just itching to drive this car and it's frustrating to be delayed by something which may (I hope) be very simple. Any advice or questions would be highly appreciated (and thanks for reading such a long post).

Sincerly,
Eric Corwin (A newcomer to these really neat cars)

[S Allen]

Eric,

Welcome the wonderful world of roadster ownership. They are great little cars and fairly easy to work on.

Over heating can be caused by several things. It sounds like you have done the obvious. The number one cause for overheating of a 1600 R16 motor is a head that is shaved too much. A shaved head will make the car run hot no matter what you try to do to it. I would put running the carbs at a lean condition as next right along with running the ignition timing too far retarded. The thermostat could be installed upside down. Do not laugh as it has happened. So, I would check the igntion timing and tweak on the carbs a bit first. Those would be the easiest fixes. One other thing to remember when filling the cooling system make sure the heater is on to get water circulating through the core. Simple but easy to forget. Replacing the old filler cap and overflow cap might not be a bad idea. They are available from any of the vendors. Dean at Fairlady sells a replacement for the rubber ring that seals the caps if you think they are still good.

The problem is it sounds like you may have gotten it hot enough to warp the head and you now may have a leaking head gasket. The later cars have an aluminum head that does not like to get hot. You can pull the dip stick to check the color of the oil. A real bad headgasket leak will turn oil into a milky looking color.

Good luck and I really do hope it is an easy fix but do not let pulling head scare you. It is not that hard if it comes to that.

Steve

[SLOroadster]

Does the car still have the smog equipment on it? If so check the distributor and see what advance cam is in it. If it doesn't say 7.5 on it, replace it with one that does. That will fix the retarded timing issue.
Good luck and have fun with your new toy,
Will

[Eric Corwin]

Hi,

Thanks for the advice, I have a pretty stupid question: When I fill the coolant system how high should the level be in the reservoir tank? I took a look at the car this morning and the reservoir tank (which I had filled to about an inch of the top) was totally filled up and the tank on the engine was empty. Also, the thermostat looks a bit funny now, the pin on the top isn't seated in the little metal crossbar but rather is resting right next to it (does this mean I need to replace the thermostat?). Is there a way to check if the thermostat is functioning without taking the whole thing apart?

I think that the carbs and the timing are probably fine, they were checked out and adjusted before I bought the car. I checked the oil and it's clean and free of coolant and the exhaust is free of steam. The water pump doesn't seem to be leaking either.


Does anyone have some pointers to a discussion of how the cooling system on the 1600 works and how to troubleshoot it?

Thanks a lot,

Eric

[Minh]

Hi,
Is there a way to check if the thermostat is functioning without taking the whole thing apart?

Eric

I not to familiar with the 1600, but the principle reamains the same. Boil a pot of hot water at or above the temperature the thermostat opens up. Pour the hot water down onto it. Use a flashlight if neccessary and see if the thermostat opened up.

Roadster thermostats come in differrent temperature breaker points from 160 to 210 degrees from what I have seen.

[S Allen]

I keep the overflow topped off as it is an integral part of the cooling system. To visually see if the thermostat is doing its thing-with the car cold, start her up and keep and eye peeled on the temperature guage. Depending on what temperature thermostat you have you should see a slight drop in temperature when it does open. Say a 180 should open around + or - 3 degrees of a 180 degrees.

There is a general cooling tech area on the main website at http://www.311s.org/tech/cooling/cooling.html It covers the basic stuff.

Wish you a simple fix.

Steve

[TR]

Hello,

Sorry to bring bad news, but I think your statement;

the reservoir tank (which I had filled to about an inch of the top) was totally filled up and the tank on the engine was empty.

spells trouble...This is very typical of an engine that has a blown head gasket (or very slightly warped head). What is probably happening is air (exhaust) is being pumped into the cooling system. This causes the system to get very hot in addition to pumping all of the fluid out of the overflow...

Some easy checks: fill the entire system *(see below), leave all of the caps off. Start the car, let it idle. Watch for any fluid movement, if either fluid levels drop, add more. Take special note of any surging of the fluid or a steady stream of bubbles. It should be obvious when the thermastat opens (a few minutes from dead cold). Fluid will begin to move rapidly through the system and the top tank of the radiator will get warm/hot. Any temperature device that measures ~180F will tell you the temperature that the thermastat opens at (sneak your turkey thermometer out of the kitchen). If you see a constant stream of air bubbles, especially a surge when you blip the throttle followed by bigger bubbles, it is time to get out the tools...

There is also a paper indicator that when placed in the coolant changes to a certain color if exhaust gas is present. I haven't seen it at auto parts stores, but I am sure it is available.

*Filling: Make sure the heater valve is open, squeeze the lower hose to circulate the air out, knock the little tab on the thermastat to let trapped air out...

Good luck with it! TR

[Eric Corwin]

Hi,

Thanks for the advice TR, I did what you said and filled the system and started the car with the caps off. Initially the fluid level slowly rose by about an inch and a half and then sat there vibrating with the engine, but free of bubbles. When the throttle opened (after 5 minutes exactly!) there were about 10 small bubbles that came up but that was it, even when I raced the engine I could see the fluid flowing quickly and raise about another inch but no bubbles (also, next to nothing was happening with the reservoir tank and nothing was coming out of the overflow valve). I think I may have put a bit too much fluid into the system as the fluid level continued to rise slowly until it began to overflow (at which point I turned off the car). So I hope this means that the head gasket is allright.

I thought that since fluid had been leaking out around the radiator cap on the engine that this might somehow be the culprit. I looked at it and the rubber seems a little warm so I cut out a rough gasket out of some thicker rubber and tried that. No more fluid leaks out now and the car seemed to stabilize temperature at around 210 or so with the car parked and running for a few minutes. I want to check the fluid levels before I run it for a while and see if it really won't overheat but I'm curious if this is a reasonable temperature for a parked car to idle at? (Also, I noticed that the throttle wouldn't always return all the way down to idle after I pulled it back with my hand, but that might be a question for another day.)

So thanks for the advice and here's hoping that I might have (temporarily, until I get a new cap) fixed it.

--Eric

[TR]

Hello Eric,

That is great news!

The leak around the radiator cap explains the loss of fluid, it is amazing how much fluid will pump out of the system.

Now you can be confident that it is probably the usual suspects...

210 is a bit warm, although typical of an older car... Check the timing, ensure that the timing and distributer cam match (look through the main site and previous discussions), ensure the radiator is functioning well, fan, fan shroud, hoses, etc...

Look through the main site for lots of great info...TR