Overheating Problem (Revisited 3)

Q: Overheating Problem (Revisited 3)

My Firebirdd is overheating and has low oil pressure. Is the low oil pressure causing my overheating problem.

A: I had problems with the cooling on my last 1968 after I rebuilt the engine. A few things to check

1.) Does the clutch fan actually work???? Mount a regular fan in its place to test to see if the engine now cools properly. I’ve never seen the clutch guts, but they can discontinue the correct lock-up and revolve at less than 100% of the correct idling speed. I have had this problem. It looks like the fan is working, but it is actually going much slower than it is supposed to, hense overheating.

2.) How long has your radiator been out of your car?? One of the oddities I have encountered is that when a radiator is romoved, crud (rust) that has circulated in dirty coolant will sometimes settle and clog the passages. Self flushing doesn’t seem to cure it, because it becomes hardened in the passages, just like a clogged drain in your house. It will need to be replaced, or removed and boiled by a pro radiator shop.

3.) You are running an anti-freeze/water mix aren’t you? Running 100% of either can be a problem.

4.) A recent article (either Old cars weekly / or classic auto restorer) discussed this topic in general. One of the often overlooked items is that engine blocks and head castings that sit for long periods of time without use had clogged coolant passages. Did either of yours sit without getting boiled out?

A: With regard to low oil pressure and overheating, that is a common problem. Here is the deal. Oil pressure is a measurement of resistance to flow (the flow of oil). The thinner the oil, the easier it flows. When your oil gets real hot, it flows very easy, hense the oil pressure drops. At start-up, the oil has a high viscosity (it’s thick), so there is plenty of oil pressure, but relatively low flow.

All automobile engines have a built in pressure relief valve, either in the pump or somewhere in the oiling system. In theory, you can never go above the max PSI as long as the pressure relief is working. The oil pressure will level off at high RPM because you have hit the limit of the pressure relief valve. At idle, the relief valve would only work when the oil is very thick, such as on a real cold day. It’s kind of weird that way. We often make the mistake of thinking that only oil pressure counts, but flow is just as important. That’s why most engine damage occurs at start up. There is very little or no flow for a few moments, even though the PSI jumps up instantly.

So, to answer your question. It is possible that your bearings are worn and the resistance to flow has been reduced from bearing clearances that are above the max tolerance. A pressure problem would normally show up first when the oil is hot and thin and at idle speed. It is also possible that your oil pump is worn and has reduced flow and that in turn is creating reduced pressure. When the oil is hot and therefore thin, the problems are likely to show up. But… my bet is simply that your car is running too hot. Get it to cool down and stay cool. Your oil pressure will likely rise to where it is supposed to be. Let the car idle, and watch what the oil pressure at about 195 degrees. Ideally, I would never want an older Pontiac engine to be above that temp. If the oil pressure at that temp is acceptable, then it’s just a matter of getting the engine to cool down to that level or lower. Beyond that simple diagnosis, we are talking removing the oil pan and checking the oil pump, bearings, etc. Not easy….

One last point. Are you running headers????? They aren’t causing the oil pan (and the whole engine compartment) to get hot are they? That situation will certainly cause thin oil (low PSI) and engine overheating. Headers are a real pain in a Firebird. No room to dissipate heat in the engine compartment! And…..by all means… check the other E-Mails and pay attention to the one on timing problems related to overheating. Solid advice!

A: First lets assume that the system is full of a coolant at the proper mixture and that a new and correct pressure radiator cap is in place. I also assume that the coolant was topped of after the engine ran and the thermostat opened.

What type of fan do you have?. If it is a clutch fan, is the clutch part still working? Are you using a radiator shroud? Is the fan set at a proper depth within the shroud? Are the original baffles in place on top of and underneath the core support? Do you have anything blocking the airflow in front of the radiator? Is it the proper radiator for the car(Not intended for a 6 cyl is it?). Have you had the system flushed to remove deposits/corrosion? Is the lower radiator hose collapsing when it gets hot? Do you have one with a spring in it?

If you are moving too much fluid with a higher volume pump there might not be sufficient time to absorb the heat. Retarded timing could cause it to run hot. Lean carb also. Has the engine been rebuilt recently? A tight engine may run a little hotter. Is there a possibility of air in the system casing cavitation/steam pockets? Is the thermostat working? Is the water pump impeller exactly the same size/shape as an original one? Is it possible that the water pump shaft is slipping and not turning the impeller at the intended speed?

Red-Line makes a product called water wetter that is supposed to reduce water temperature. I believe that it reduces the surface tension of the water allowing more of it to contact the metal surfaces. I think they claim about a 10 -20 degree F drop (bought mine at a auto part store). I think it helped, but can’t remember how much. It is about $7 US. (clear bottle pinkish-red fluid).

Have you tried an external oil cooler?

Has it ever run at the proper temperature? If so what have you done to it since then?

A: Back to a few basics….. What happens when the temp in your car rises???

Crap happens:

Compression maxes because the rings seal really, really tight. Try disconnecting everything (electrically from ignition circuit) and crank your engine over by hand, you’ll see the difference in resistance. Of course, you can also test this with a compression tester. Bottom line, the engine is tough to turn over.

Okay, we all know the obvious, the starter is at max stress because high temp causes high resistance in the electrical windings / armature, meaning less than ideal starting.

When the engine turns over (barely) preignition occurs and it says No go! No go!

So…. What is the answer? Don’t even think of fixing it with a starter solution. There is only one real answer…. Get the temp down…..

You can diagnose until you are ready to puke, but here are some steps I take to ensure I’m going in the right direction. From the cheapest to most expensive solution.

1.) You are running 10W40 oil. A grade of 10W30 or less will aid in the rise in engine temp.

2.) Run a blend of anti-freeze and water per the coolant mfg recommended mix

3.) Be sure to run a thermostat (don’t run without it or the coolant will not have time to cool properly).

4.) Your timing is correct isn’t it? To much timing will making it overheat faster than you can say boilermaker. I also include correct point gap in that discussion.

5.) Your radiator isn’t even slightly plugged is it???? These are 30 year old cars. If your radiator is more than 10 years old, chances are some of the cooling rows are plugged. Have it professionally rodded out. Home mechanic cleaning materials are a joke on a radiator this old. Oh and if the radiator was removed an let to sit long enough for the sludge crud to become hardened in it, you are in for a super plug job.

6.) Your fan shroud is installed properly isn’t it??? I won’t say any more on this one.

7.) Get rid of your headers!!! Oh no… the evil of such discussion. Headers in most birds cause a problem with oil temp rise and underhood head (causing coolant temp rise). They are too close to all of the mechanicals and the starter in a bird. I have installed and removed them in several birds. That step alone can solve the problem. Consider using the HI perf manifolds for 68.

8.) If you must run headers, install an oil cooler and 4 row radiator. That will help. It may or may not solve it.

9.) Your engine isn’t worn to the point where the bearings are bad, or it has a bad oil pump, is it??? In either case, you will suffer reduced oil pressure and the problem compounds the longer the engine runs. The engine will begin to overhead from additional friction caused by reduced oil pressure. The hotter the engine, the thinner the oil gets, making flow easier and pressure worse. The only solution is to replace the problem components in your engine.

Any proposed updates, changes, pictures, and/or corrections, please use our comment section below (may need to click on permalink to access comments feature). Information is subject to change and offered as is without any warranties or guarantees. Please review our Term's Of Use for more information.