Radiator has me absolutly confused

[Tyler Atkinson]

I will never claim that I have expert advice, but I do own a 1976 Cadillac Sedan Deville with an HD radiator that actually likes to run 4 quarts low on coolant, and the only thing I can think of (running this by multiple mechanics across multiple repair shops) is that the reservoir is broken or it actually likes to run low on coolant (don't ask me why). I am rather curious if anyone has had similar symptoms, or if this is an unusual first.

And one more thing I would like to say is that it actually runs colder with about 4 quarts less coolant.
I have the 25.6 quart system vs. the 24 quart system if that makes a difference.

If any additional details are needed please ask, as I don't want to run a 500 CID into the grave.

[Tyler Atkinson]

One thing I forgot to mention is that it also wants more engine oil. Believe it or not, it would hold 5 quarts without a complaint and now it wants over 6 quarts and won't stop setting off the engine oil light. I am utterly confused and have no idea why anything about what I am saying makes sense, but this is happening and I will gladly post picutes for proof if that is what you need.

[The Tassie Devil(le)]

G'day Tyler,

Firstly with the coolant, check the radiator cap to see that it is working correctly, and is a recovery-type cap.

If it has been replaced with a non-recovery type, or has an internal leak, then it will spit the coolant out into the recovery tank, but not allow the cooling radiator to suck it back in as it cools down.

Now, as far as the oil goes, I would be putting in a temporary oil pressure gauge and seeing what the oil pressure really is.

But, you could also have a cracked oil pickup that won't really suck enough oil till the problem hole is submerged.

Lastly, the internal passages could be that plugged up with carbon and sludge that the oil is taking a long time to return to the sump from the top of the motor, hence trhe need for more down below.

How many miles has the engine run, or how few miles, as lack of use could cause problems of sludge build-up as well.

Bruce.

[Tyler Atkinson]

Thanks for the speedy reply.

As for the radiator cap, it doesn't even have 500 miles on it, and I paid for the best of the best at the time which is a performance radiator cap (Not sure of the absolute specific specs on it, but it hasn't let me down).

As for returning coolant to the tank, that is the exact issue that I have been having, but what has utterly confused me, to a point of bewildered, is that the heater runs colder than it ever has. I have filled the tank to full, and I will have the climate control blow 100 degree air on my legs, but it blows 80 degree air, I kid you not, when I let the radiator run low on max heat.

As for the oil issue, the pressure guage seems to be working, as it will only go off when I break really hard or hit a turn harder than  normal. I can guess that the oil shifts enough in the pan that the pickup can get it, but from your information, I may need to closely inspect it. As I said, I don't want to run this car into the ground at all.

As far as running, I bought it at 112,000 miles aprox. and it is now at about 130,000 miles.
I have spent multiple figures into getting this beautiful vehicle running flawlessly, and I do not want anything that could cause this magnificent engine to fail to happen. In that time I have done a full upper engine rebuild, replaced the alternator, 3 batteries (long story I will gladly share over  PM), 5 starters (another long story), 2 coolant flushes, a complete rear end rebuild, a nearly complete front end rebuild, 6 oil changes, full drive line rebuild, rewiring the headlights, and a few other electrical confusions that don't concern me, and if anything that I think is trivial at the time that might be important I will gladly share. Otherwise I don't really know what else I could post on this fine motor vehicle.

I really love this car and don't want to damage anything that can be repaired before it is too late.

[The Tassie Devil(le)]

There are radiator caps and radiator caps, and it all depends on which style you have that correctly fits your radiator.    And there are many best of the best, but there are different styles - recovery and non-recovery types.    Pressure-wise, you should be looking at around 13 to 15 Lbs pressure, and a double sealing ring.   One for the base, and the other one part way up the side to pressurise the upper outside diameter of the cap housing.

Check the overflow hose from the radiator to the recovery bottle, and see if there are any holes in it, plus the pickup inside the cap to see that it is ion there, and reaches down into the bottle.

Losing oil pressure on turns and hard braking, with the correct amount of oil in the sump rings loud bells of alarm.   No matter how hard you turn the vehicle, the oil level should never leave the oil pickup.

Something is definitely wrong somewhere down there, and about time to drop the sump and investigate.

Bruce.

[TJ Hopland]

The stock oil pressure light comes on in the 3-5 psi range.  At idle a well broke in engine can live a long time at that pressure but if you are that low off idle its going to have problems.    The level thing makes no sense and a cracked pickup is not that common of an issue but could explain it.  The factory cam timing sprocket was covered in a plastic which age and mileage (which you have plenty of both) was not kind to.  Many of us have seen them were there is no plastic left on them at all and they are still somehow running.  All the plastic chips end up in the oil pickup and would have to significantly restrict it.  Again this does not directly explain the level thing unless like someone else suggested the engine is so full of sludge that it just takes that long for the oil to work its way back down to the pan that you need that extra in there.   If it was mine I think I would be temped to pull out the distributor for a look.  With the distributor out you can see the top edge of the cam gear and chain.  This will give you an idea if its condition and also the overall cleanliness of the engine.  If you cant tell anything by looking down there you may have a filthy engine with a shot cam sprocket.   Its actually pretty common to find these cars in this condition.  They were often reasonably well cared for when they were new and their owners were younger but often they were the owners last car so when the owners were still able to drive it was often short trips which are hard on any car and then the cars often sat for many years while the owner(s) were perhaps having medical issues that they hoped to recover from.  Eventually the cars are handed to other family members that dont appreciate or care for them which is hard on them and that is then the point where we pick them up.



Your coolant issue is also interesting.   I have had many vehicles that would never keep coolant in the expansion / recovery tank but unlike yours they would generally keep the radiator almost full.   On most of them I just got used to it and did not ever spend that much time trying to figure it out.   Have a few more questions on this coolant thing.

IF warm up the engine with the cap off and fill it to the top then fill the tank about 1/2 full how long will it take before it gets down to this lower level 'happy' spot?   Is it just heat cooling (overnight) cycles?  Miles? 

Do you ever see any leaks?  Or does it just seem to disappear?   IF leaks where do you see them?

I'm going to start a thread on radiator caps so this one does not stray too far off topic.