PM70

Sorry I haven't been here in a while. Ya know, life and all. Also, haven't had any issues with my 70CS until now, and would like some input. Seems that she's been running hot and using up water - I find I need to top of the radiator every or every other ride, and I try to run it her at least once per week. This is a recent issue, and other than it being 90 degrees out all the time now (I relocated to North Carolina from NY about 9 mos ago), I don't see any leaks or anything wet in the engine bay. Its been 30+ years since I've done even basic work on a car and could use a refresher and some thoughts on this please, before I take it to a mechanic. Thanks!

72455

Is it overheating and when you say water, do you mean straight water or a 50/50 mix?

BangScreech4-4-2

1) Any white exhaust smoke?
2) What does the coolant look like?
3) What does the oil look like?

Vintage Chief

Curious to know how you initially suspected you had to top-off the radiator fluid? Did the hot temperature lamp on the dash panel illuminate and you suspected an overheating condition?
Were you simply checking on things and decided to examine the level of radiator fluid and noticed it was low, then continually checked it over a period of time?
Has it in fact ever overheated and boiled over with rushing fluid?

Sometimes you'll get radiator coolant heating up and small amounts of fluid begin to heat up and run out the overflow hose while you're driving - never a pool of fluid on the floor.
If it were the thermostat (as in the thermostat was closed and inoperable) you'd most likely result in a violent overheating condition - which I don't believe is your case.

What I do suspect is the possibility your radiator cap is not holding pressure in the cooling system and you're getting blow-by overheated radiator fluid running out the radiator overflow hose while you're driving as the result of not operating under pressure.

A simple way to initially perform a quick check on this is to take the car for a 10 mile ride until it's warmed up to operating temperature - the coolant should be running through the engine and radiator under pressure. The key here is under pressure. To determine if the coolant is operating under pressure (which it is designed to do), with the engine still running grab and squeeze the upper radiator hose - the hose should be firm - you should not be able to collapse the hose. This will demonstrate the cooling system is operating under pressure. If you find the upper radiator hose collapses easily while squeezing it, I would suspect a defective radiator cap. The radiator cap should be a 16lb pressure radiator cap. Buy a new radiator cap rated at 16 lbs of pressure, install, perform the same test and see if the upper radiator hose is now firm and hard to collapse.

PM70

I'll try to answers all questions here:
- no white smoke
- both coolant and oil look fine
- I've been adding straight water at the moment, until I'm able to get some coolant
- I knew I needed to check the radiator but yes the HOT lamp illuminated the other evening while sitting too long at a drive through (how did it know I was about to check the levels?). There was excessive heat from under the dash, the windows started to fog and I could smell antifreeze.

The next day I checked and the water level was really low. I filled the radiator, let it settle and filled it again. Took it for a 30 min ride yesterday, let it cool, checked, and needed to add add'l water.

I was also thinking radiator cap. It is 49 years old, and seems like the simplest way to start.

Jamesbo

Check the carpet on the passenger side floor board. Is it damp/wet?

Vintage Chief

x2 what James is asking - might be the heater core

For the time being, read this article for heater core symptoms - it's rather well written and describes the symptoms.

Five Signs You Have A Bad Heater Core

Tedd Thompson

X3 if you have fog from the defroster vents it almost always means leaky heater core..... Tedd

Vintage Chief

Here is a recent thread regarding heater core replacement in case you find yourself moving in that direction. I'm just providing it for you now as a means to help you understand/identify what may be the issue, time involved and the possibility of bypassing the heater core until you can get it fixed (if this proves to be the issue). There are many threads on heater core here - this one is the most recent.

https://classicoldsmobile.com/forums...cement-135697/

troyd

Do you have an overflow jug? If not.....dumping out the overflow tube is a distinct possibility.

I would suspect the leaking heater core as well.......a wet passenger side footwell is a dead giveaway (and on a 49 year old car it's very likely)

However, I have been the victim of a head gasket failure where the symptoms were pretty mild. No mixing of coolant and oil......a little smoke on start up but nothing that couldn't have been explained as condensation. However, the gasket failed and a little coolant was finding it's way into one of the cylinders.

I'd rule out the obvious things (radiator cap, heater core etc etc) first and don't go having someone pull the heads without ruling everything else out first....but losing coolant and not being able to find it makes me paranoid.

Cheers,

Troy

FN723

I have a Chevrolet van that I once had to add coolant frequently. I couldn't find a leak and there was no white smoke. Then a few months later I had a lot of white smoke, the head gasket failed. I know now the head gasket was failing and wasn't getting enough water in the cylinders to make enough smoke to show.

Charlie Jones

Per the 1970 Oldsmobile Service Manual ;
" Keep coolant level to "fill cold" mark on radiator .Check only when cool . "
The radiator should not be entirely full when the engine is cold . You must leave room for expansion .

Fun71

As others have already said, that translates to a leaking heater core. Every time my heater core has leaked (it's been quite a few since the 1980s) the fog on the passengers side of the windshield was the telltale sign.

w-30dreamin

What Charlie Jones says.
You may not be low,you may be over filling your system and it's pushing it out while driving,then when you check it,you think it's low because you have lost some.
Look on your radiator tank,there is a full mark on the outside to give you an idea how high the level of coolant should be.Topped off is not correct.
On my radiator the full line is just above the upper trans cooler line on the passenger side of the car.
Everyone wants to start diagnosing problems you may not have,sending you on a wild goose chase. The first step is to make sure you understand how the system is supposed to be used and function.

Fun71

Good point on ensuring the radiator is filled properly (assuming he doesn't have an aftermarket overflow reservoir like my car has), but I don't see how coolant out the overflow hose would make his windows to fog.

oldcutlass

You probably don't need another person to tell you your heater core is leaking as by now you've found the wet spot on the passenger carpet.

w-30dreamin

Sorry I missed the post about the window fogging.

Schurkey

Troyd and Charlie saved me a lot of typing. Thanks, guys.

Every car I own gets an overflow jug and an overflow-style rad cap. There is no reason to NOT have an overflow jug except for excessive cost-cutting by GM.

PM70

Thanks for the advice everyone. Comments regarding filling the radiator to the correct level plus the fact that I've been running the car lately in 95 degree heat without any problems has lead me to the following conclusion: I remember trying to check the coolant a day or two prior to the issue that started all this (HOT lamp, fog, smell and very low on coolant), but I wasn't able to budge the radiator cap bare handed so I left it for later as I was in a rush. Now I'm thinking it moved just barely enough to let coolant evaporate that hot evening.

Ive run the car several times since plus almost an hour today in 90 plus degrees, and each time the coolant has remained at the same level in the radiator, especially now that I've been reminded as to where that level should really be.

So I'll save myself some time and money for the moment and just continue to check the radiator every few rides, and keep my fingers crossed. Without everyone's comments here it would have surely been in the shop by now having everything replaced, and just making my wife mad that I was spending money on it.

72455

Ahh...the old "sometimes the hardest problems are the easiest to fix" diagnosis....been there done that.
Are you kicking yourself in the butt?...lol

Glad to hear you figured it out😀 and thanks for the follow up post.

oldcutlass

What about the fogging of the windshield in side the cabin?

PM70

Ha ha You know, as soon as I touched the cap the first time I knew right then and there here was going to be more to this....

PM70

Only happened that one time.

BangScreech4-4-2

If there was coolant vapor coming from the defrost vents (even just on one occasion), that's a very strong indication of a rotted and leaky heater core, which wouldn't be a big surprise on a half-century-old car. Make sure your passenger side carpet is dry.

troyd

Anything being possible but I'd keep an eye on it as coolant where it shouldn't be generally isn't generally a one and done thing.......

Again, pay attention to the front passenger side foot well......the good news is that you can bypass a leaking heater core as a stop gap measure until you can get it properly sorted.

Cheers,

Troy