74 NovaMan’s … Novas

[Scott Liggett]

Sounds a lot like an air bubble in the block. I drill two or three 1/8 or 3/16 holes in the thermostat. It allows air to escape pretty quickly.

Also, if you are still using the old radiator cap, get a new one.

[TheSilverBuick]

I do typically drill ~1/8th inch hole in the thermostat, however I find the results mediocre. I think because it bleeds air too slowly, hence why I switched to pulling the heater hose. I still do the ~1/8th inch hole anyways out of habit and I don't believe it hurts anything.

[74NovaMan]

The swings, especially on the way down (from 220 - 180), took only seconds. Seems to scream air bubble doesn't it?

Ever drilled a hole in the thermostat to eliminate trapped air?

[TheSilverBuick]

I don't believe a fan can cause rapid temperature oscillations. Either slowly heat up or slowly cool down over a period of a few minutes.

[74NovaMan]

It has worked fairly well in the past. It has got to be the thermostat or an air bubble.

Thanks for the ideas guys.

[STINEY]

I remember some flex's getting a bad rap for performance.....maybe you have one of those?

[74NovaMan]

Flex

[STINEY]

Only if you are chasing MPG or reducing engine noise. I personally like things simple - never much cared for clutch fans.

Is your fan a solid or a flex? Looks like a flex from the picture?

[74NovaMan]

No fan clutch. Maybe I should get one?

[STINEY]

Fan clutch failing? Had a 231 in a '78 Buick Regal do that once......

[74NovaMan]

Thanks for the ideas. I had a good mix of driving in town and freeway. I don't seem to be losing coolant anywhere. I did check for heat when it was reading hot and that seemed fine. I'll try heating it up to temp with the cap off and see what happens.

[TheSilverBuick]

I'm open to hear other ideas, but I really doubt it's the thermostat and even less so the temperature gauge. When thermostat's fail, you either get really really hot and no cool down or the engine simply does not warm up.

[TheSilverBuick]

Different driving pattern? Highway driving? Staying above idle rpm keeps the water pump moving the water more efficiently and the system under more pressure to keep the steam at bay and the coolant higher up (against the sensor and thermostat). Stop and go will start and/or aggravate the oscillation and continuous rpm/speed will dampen it and make it go away over a couple miles.

I don't know if you have a heater control valve or not, simply using versus not using the heater could of done it if you have a valve.

A possible leak in the system some where?

And lastly, IMO, 120 miles isn't much driving time, especially around town driving where it never really heats up.

[74NovaMan]

Any thoughts on why it would not do that for 120 miles and start now?

[TheSilverBuick]

Not the gauge. What happens is a steam pocket forms and the steam is at 212+ as it's easy to heat steam, hard to heat water/coolant, also steam is a poor conductor of heat, so it's against the thermostat too, but slowly heating it enough to open. Once it opens though the water pump can pull the cold water from the radiator in, which pushes the steam out to the radiator and the temp sensor get's hit with cold water as does the thermostat that then slams shut and the process repeats.

I'd top off the coolant with the heater hose removed, then fire up the car with the cap off and watch the coolant level in the radiator. It'll probably spill over right around the time the thermostat opens, but then the coolant level will drop like a rock. At that point you have to be fast to fill the radiator. It's a good practice to leave the level an inch or two below the fill neck, it keeps it from spilling or blowing into the overflow bottle more often. I've had good luck with the heater hose removed method, and the coolant level NOT dropping like a rock but very clear when hot water was starting to enter and flow fast through the radiator. Usually only drops an inch or two then.

Follow up check is on the functionality of the radiator cap. If it's weak it'll allow the steam pockets to form more easily versus having pressure to keep the coolant in liquid form.