1984 F150 with 302

I've got some good blow by coming through my oil cap and even my dipstick. I'm starting to notice my temp Guage rising more than usual and my oil pressure is higher than usual. I have no idea what temperature the engine is at and what the reading is supposed to be on the oil pressure Guage but typically my temp says the engine is usually cooler just at the beginning of the normal mark and my oil pressure stays around the "O" on NORMAL when hot. Someone please tell me what the ranges are on these Guages and if you can give me some insight on my blow by condition.

Billy

 

I will start with the not so good answer
Blow by = motor rebuild time or replacement
There is nothing that can fix blow by as compression is making it pass the rings and into the crank case and out the breather and dip stick.
Have you checked the breather in the air filter track?

The factory gauges are a guess at best what is going on.
The owners manual may show where the needle should be for normal
Only way to know what the coolant temp & oil psi is is to install aftermarket gauges.
Dave ----

 

The stock guages are basically monitoring tools. The Normal range is just that. Temp varies from start up cold and when at operating temperature, say 180 to 200 degrees the guage will be somewhere between the O and the A. Since the temp guage works by monitoring resistance in an electrical circuit that resistance value can be influenced by several things. The majority of that "delta" R is in the sending unit. Some R can result from loose or dirty connections and ambient temperature of the circuit. You can get an idea of the engine temperature readings by calibrating what you see on the guage with an actual temperature reading. This can be easily done with an infrared thermometer pointed at the thermostat cap.

Your temperature reading is on the low side so you might want to check your operating temp with the thermometer. If your thermostat failed open and is not allowing the engine to reach operating temperature that can cause additional blow by as the rings are not expanding out with heat. Did your blow by condition start suddenly? That might indicate a bad thermostat and you are running cold. There will always be some blow by and that can normally be recycled through the engine via the PCV system. If you don't have vacuum on the PCV you can see more coming out the filler cap and dip stick. Doing a compression test can tell you something about the wear on the rings and valves. Time for a rebuild?

Oil pressure can vary a lot too from cold start to highway operation warm. The oil pressure guage also works on delta R. When this monitoring system is working properly you should see the guage in the middle of the range cold at idle. As the engine warms it will be at the lower end at idle but at highway operation will come back up to mid range. These guages are monitoring tools, similar to idiot lights but they do give you more information about changing Temp and oil pressure.

I would get the infrared thermometer and check, calibrate, your temp guage. You may find that your sending unit needs replacing or your connections need cleaning. You are reading cold by the guage and that can cause blow by.

If you find you are running cold you'll want to replace your thermostat.

 

As El Presidente for Life of the Stock Gauge Anti-Defamation League (SGADL), please accept my hearty thanks for your impassioned defense of the factory gauge system. With your words as the wind beneath our wings, we shall crush the bourgeois running yellow dogs who stand in our way with their knee-slicing aftermarket gauges! Long live the people's revolution!

One minor caveat for your excellent treatise, though. The cap is typically located on the cool side of the radiator. With a cooling system in good working order, coolant temperature generally drops about 30F passing through the radiator. The temp gauge (whether stock or aftermarket) monitors the hottest point in the system, at the thermostat housing. That's the best place to point your infrared thermometer. On some engines, this is not practical, as the location is buried. The next best spot is the hot side of the radiator (at the inlet - upper hose), but you have to be positive the thermostat is open.

 

When I said thermostat cap I did mean cover or housing. But yeah taking temps on both sides of your radiator is a good idea too, to see your temp drop across it the coldest spot there would be near the bottom hose. Yeah once you get one of those infrared thermometers there's no end to finding things to point it at.

 

How bad are the symptoms? As Dave said, blow-by increases as the engine wears out and the piston rings aren't sealing as well as they once did. I'd suggest doing a compression test to get an idea. If not too bad, and the truck sees minimal usage, you could go for years like that.

I did just that with my 351W. I'd do a compression check once a year. Other than a little oil collecting in the air cleaner housing, all was good for many years like that.

Is your Positive Crankcase Ventilation (PCV) system intact and functioning? This does a good job of extracting oily fumes from the crankcase. Sadly, this highly beneficial system commonly gets ripped out when somebody joins the "Rip Out That Pollution Crap" club.


​​​​​​​​​​​​​​If two gauges are reading higher than normal, this could be a separate problem with the Instrument Voltage Regulator (IVR). This device feeds the oil pressure, coolant temperature, and fuel quantity gauges. If the fuel gauge is reading high, you may not necessarily notice.

 

I believe that your status as El presidente for life extends into perpetuity, similar to another famous Karl, who's name will be echoed into the world's great halls for some time to come...

 

Forgot one important detail:

If a compression check is good and the blow-by is not too severe, and you decide to just live with it, plan to change the oil a little more frequently than normal. Not a huge deal, but the oil will tend to get dirty more quickly.

 

1st thing I would check is the PCV valve. It should suck on your finger when you pull it out of the valve cover with the engine running. It's what sucks those gases out of the interior of the engine.

 

I'm a card-carrying member of that club and it never would have occurred to me to remove the PCV system... that's just stupid from so many angles.

...maybe that's why they haven't taught me the secret handshake yet...