It's getting cold and I've been running the heater in my 63 almost every morning. Lately, though the heat is intermittent. The fan blows, but it'll go between blowing hot and cold air. Seems that it blows warm and first and then starts to blow cold after a bit of driving. Not always, but usually sometime before I make it to work it'll start blowing cold. Sometimes it'll kick back to hot for a mile or so.

The core is not leaking from what I can see. I've checked the hoses in the engine bay and they are hot, so I think it's circulating. Maybe there is some sort of clog somewhere? Before I start tearing anything apart does anyone have suggestions as to where to start?

 

I'd start with the basics.

A few things to check:
- coolant level
- maybe a blockage in the heater core?
- thermostat
- hvac controls

When I first bought my 75, upon inspection I noticed there was a vacuum line off near the blower motor. Once that was connected, it started blowing hot air as expected.

 

^^^THIS. In my experience the random temp is almost always caused by air pockets in the cooling system.

 

I've had this happen running a 160* thermostat.

 

If you're running a 160 t-stat, the coolant will be 160 or hotter. That's not the cause.

 

The first thing I thought of was the coolant level, so I topped it off. I even flushed the system and topped it off after it started to happen. Maybe air bubbles?
The second thing I thought of was the thermostat and water pump, but I've had no cooling issues and I can tell there is water flowing through the radiator. So not the water pump or the thermostat.
The havc controls work as it will blow hot sometimes. It will even go cold and then hot at random times throughout the drive.
I am leaning toward the core being blocked up or dirty as well.
I am definitely going to triple-check all of the mentioned, though.

Thanks for the advice.

I have no clue what thermostat I'm running, my guess is the original based on everything else on the car. It's worth cracking it open to double-check, though. Easier than pulling the core and checking it.

 

The water pump isn't the issue. If the water pump is failing, the puddle of coolant under the car would be the tip-off. And as you noted, the car isn't overheating, so t-stat isn't an issue either. If you are SURE there are no air pockets (and I sometimes run the car with the nose elevated to force air bubbles to the radiator fill point), then check for blockage in the heater core or a broken cable controlling the temperature blend door. And just so we're all on the same page, a 1963 WHAT? Full size? F85? With or without A/C?

 

I had a 88 acura integra for a few years. At the beginning of every winter i hade to back flush the heater core. Other wise the heater would work exactly as you described. I would just back flush it with a garden hose a few times and it was good all winter.

 

I'm not convinced there are zero air bubbles, now that we've been discussing it. I did everything I could to prevent it, but I've never actually verified that. Never thought about the blend door either.

This is a 63 ninety-eight custom sport. 394 ultra-high compression with A/C.

 

right from the hose in the engine bay or how did you get to it?

 

Disconnected both heater hoses from the core and put the hose up to the outlet side. You could make up some kind of adapter i you wanted to.

 

You can get a flush kit for your radiator/heater core at any parts store.



Right next to it on the shelf should be a large funnel with various fittings that connects it to multiple radiators. This allows you to belch the coolant system an ensure there aren't any air pockets.

 

Does the car have a heater control valve? I should know since I have a 1964. My 1959 98 has one and it is vacuum controlled by the temperature lever on the dash. Maybe if there is a heater control valve a vacuum line which opens it and allows coolant into the heater core is loosing vacuum at times and then it closes.

In a 1959 394 V8 the heater control valve is on the passenger side on the rear of the engine and it has vacuum lines going to it.

Other than that I agree with air pockets in the coolant. Also the thermostat temp just means that's when it opens and allows coolant to flow freely. So the temp is not limited to that rating. I get tired of hearing people thinking that keeps the car cooler.

Also I am assuming full size Olds, this is a 98 forum.

 

That is true on a hot day, not when the outside temps are cold.

 

If you're running the original thermostat you may (easily) qualify for entry into the Guinness World Records.

 

I definitely need to grab one of those kits. I just flushed the radiator, but that was it. There is for sure a bunch of garbage in the system.

I have not had time to check on the control valve yet, but it is on my list. I think it does have one, though.

It's got 59,000 original miles and everything I am finding on it is original. It looks like someone found it in a garage or barn and did a Craigslist rebuild to it. But it is evident by the leaves that were painted red right along with the intake and how everything else is painted black under the hood. Including the belts, washer fluid container, etc.