Overheating, drop in oil pressure when coming to a stop

I just bought a used vehicle and noticed that when i come to a stop and ive been driving for a while, the engine will start to overheat, a/c wont cool, and the oil pressure gauge will drop. Can you give me opinions on what this could be? My cooling fan works and im not loosing coolant, that i know of.

My car has 204000 miles.
My car has an automatic transmission.

Experienced mechanics share their insights in answering this question :
I would start by checking the thermostat. If this is not working correctly, the car will quickly overheat. Driving may temporarily keep the temperature down due to wind circulation, however once you are stopped this goes away, especially if the coolant is not flowing properly.

You may also have a problem maintaining oil pressure as you mention a drop when you come to a stop. As you know as engine RPM’s are higher more oil pressure is maintained and thus temporarily keeping the oil pressure up, however if there is not enough when the RPM’s come down so will the pressure.

I would check the oil pressure sending unit as well as the oil level itself to be sure:

You have enough oil.
the oil pressure sending unit is working properly.

As to the A/C, you will want to check to be sure there is enough refrigerant in the system, check the A/C relays to be sure they are coming on at the right times, etc. I would recommend having an expert from Your Mechanic coming to your home to diagnose your overheating issue and repair.

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

The most common reasons a Jeep Grand Cherokee is overheating are a coolant leak (water pump, radiator, hose etc.), the radiator fan, or a failed thermostat.
In general, it`s because something`s wrong within the cooling system and heat isn`t able to escape the engine compartment. The source of the issue could include a cooling system leak, faulty radiator fan, broken water pump, or clogged coolant hose.
The most common reason a Jeep will run hot is due to low oil or a coolant problem. Low coolant is usually because there is a leak somewhere in a hose, the reservoir, or the heater core. A failed engine thermostat or a blown head gasket are other common causes of overheating Jeeps.
Engine Overheating

Without sufficient oil pressure, your car`s engine will operate with decreased lubrication and increased friction resulting in more heat. Engine overheating can be a complex issue. While it doesn`t always mean low engine oil pressure, low engine oil pressure can lead to an overheating engine.

One of the most common reasons why your engine overheats when your AC is on is a faulty engine cooling fan, fan switch, or fan motor. A bad engine coolant sensor, an overloaded AC compressor, a broken water pump, and blocked AC condenser fins can also create overheating issues.
Without the right amount of oil, your engine becomes more vulnerable to overheating. Since there`s not enough oil circulating through the engine, there`s no way for the engine to shed that excess heat. This can lead to heat soak, where certain engine components overheat and eventually deform due to the stress.
High oil pressure is an indicator that the oil is not able to properly pass through the bores and reach all parts of the engine effectively. An engine that is not lubricated correctly can face (sometimes instant) wear through friction, damage to its components, and in extreme cases, it can lead to engine failure.
A bad expansion valve will cause your AC to make clanging, squealing, or banging noises that worsen over time. Therefore, if your AC starts producing odd noises while it is still operational, reach out for help as soon as you can.
A car`s thermostat is part of the Jeep Grand Cherokee`s cooling system, the thermostat regulates the engine`s operating temperature and flow of coolant circulation through the engine.
Put your car in neutral or park and then rev the engine. This makes the fan and the water pump work faster, which pulls more air and more water through your car`s radiator. This increased circulation cools down the engine.
Only Use Water In The Radiator In An Emergency

If it`s really low or actually empty, you need to add fluid to your vehicle. While it`s ideal to add a 50/50 mix of coolant and water (or a pre-mixed coolant), if you absolutely have to keep driving, you can add water to the radiator to get you to your destination.

If you notice that your engine overheats, the coolant temperature sensor could be the problem. At times, the coolant temperature switch may fail such that it starts transmitting hot signals permanently. This causes the computer to erroneously counterbalance the signal, thereby causing the engine to misfire or overheat.
Thermal breakdown occurs when a car`s internal heat causes a chemical reaction in the motor oil, which causes the oil`s viscosity to change. The high level of heat actually causes the oil to degrade, or break down.
Repeated overheating can be a sign of serious engine damage. Repeated use of an overheated engine can accelerate that damage rapidly. In extreme heat, core parts of the vehicle`s engine can crack, warp, and fail — resulting in instant death to your vehicle`s powerplant.
The most common reasons a Jeep Cherokee is overheating are a coolant leak (water pump, radiator, hose etc.), the radiator fan, or a failed thermostat. Coolant leak (water pump, radiator, hose etc.)
Yes, an oil change can help prevent your car from overheating. However, an overdue oil change is not the only possible cause for an overheating engine.
Without oil, friction will cause the compressor to heat up and will cause the air conditioning system to shut down. The compressor will also leak a lot of air if there is no oil to act as a sealant. The moving parts inside the compressor also benefit from the oil as it they are lubricated too.
When too much oil is in the engine, the crankshaft`s rotation whips the oil up, mixing air into it. It causes the oil to be bubbly or frothy, and the oil pump pickup tube can`t draw oil in properly. The result can be low oil pressure – kind of ironic, isn`t it?
You shouldn`t drive with a failing oil pump for too long or you will risk damaging the crankshaft and the camshaft bearings. Additionally, driving with a bad oil pump implies a lack of lubrication which could damage the car`s hydraulic lifters.
Leaking in the vehicle`s oil passages can also lead to low pressure. Internal oil leaks can be caused by a myriad of factors, including worn piston rings and valve seals or PCV valve failure.
High oil pressure causes thick oil and debris to build up and block this flow. This buildup leads to overheating and harsh scraping between your car parts, which can lead to cracks in your engine and long-term damage to your car.
Low Level of Oil

If the level of oil in your engine drops, then it becomes harder for the oil pump to continue to manage consistent oil pressure.

Overheating is one of the main reasons why compressors fail, and it is usually caused by not enough refrigerant in the system.
Dangers of Overheating

The compressor is the part of the AC that pressurizes and heats the refrigerant gas. The refrigerant absorbs heat from the house as part of the cooling process. Therefore, if your AC overheats and the compressor is damaged, the AC won`t cool your house efficiently.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

lost all oil pressure, replaced the oil pump, low oil sensor, oil pressure sensor, oil pan gasket,
ANSWER : The fuel pump will not stay on if you loose oil pressure. This is why it is shutting off. The loss of oil pressure may be from bad crankshaft bearings or camshaft bearings. The engine oil pan should be removed and the oil pump needs to be checked to ensure that you put in the pick up tube seal to the pump and connected the pump to the block. Then remove at least one main bearing cap and inspect the bearings for excessive wear and crankshaft damage. If you need some help with this, consider YourMechanic, as a certified technician can help diagnose the issue with your oil pressure firsthand and help you fix it accordingly.

Truck has oil in it but when i am idling at a stoplight, the oil pressure gauge drops and says low oil 2003 Dodge Ram 1500 4.7L
ANSWER : Hello – assuming an adequate oil level, which you have checked, there may be a real oil pressure problem. It’s worth checking with a know working oil pressure gauge, so that you can get the real readings (i.e. 40 psi at running RPM, 10 psi at idle – both hot – would be acceptable). It’s expected that your oil pressure will drop at a hot idle, as long as you have good pressure above idle. Low hot pressures all around are indications of excessive connecting rod or crankshaft main bearings, camshaft bearings, or oil flow bleeding off elsewhere in the engine. For professional assistance, I recommend a low oil pressure inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, and give you an accurate assessment of damage and cost estimate for repairs.

My car has low oil pressure. I’ve already changed the oil pressure sensor 3 times.
ANSWER : If you have replaced the sensor three times and it did not fix the problem, then you may have problems with the oil pressure being low at idle due to wear in the engine bearings. The reason it would be fine sometimes and not others may be due to engine load and temperature changes. Have the oil pressure tested at the sensor port to see if it is low and needs engine repairs.

I recommend having a certified mechanic, such as one from YourMechanic, come to your location to perform an inspection to determine why the Oil Pressure Light is on.

Low oil pressure light comes on when idle. Check engine light is on as well. Both came on after getting an oil change 3 days ago.
ANSWER : It is possible that they put in the wrong viscosity oil. In rare instances, a defective filter will also cause low pressure. If there is too much oil, it will aerate and cause low pressure. Be sure the oil level is really not above "max". The P2187 code will appear if the oil fill cap is not tight but it will also appear due to a myriad of causes because that code only "generally" identifies a lean running condition. Consequently, numerous parts would have to be tested including the O2 sensor, gas cap seal, manifold air leaks, any vacuum leak anywhere including PCV and EVAP systems, exhaust leaks, and fuel system faults such as failing fuel pump, clogged filter and more. Since the car has relatively low mileage, you would not expect a failed oil pump, although the pressure sensor (or switch) could be bad. However, the occurrence of the oil pressure warning light is quite coincidental to the oil change, thus I would suggest bringing the car back and asking them to redo with a new filter and double check the viscosity of the new oil that they use. If the problem persists after that, you will have to test actual operating oil pressure (at idle for instance) as well as the oil pressure switch. Finally, if the oil pressure warning light comes on continuously, unless the warning circuit itself is malfunctioning, that means the oil pressure is too low to operate the engine without damaging it. Anytime the light comes on for more than literally an instant, you should shut down the car and thus an issue like this obviously has to be repaired.

If you’d like, a YourMechanic certified mechanic can come to your home or place of business to inspect the vehicle and perform an oil pressure light is on inspection to diagnose the vehicle and suggest potential repairs.

Truck dying and oil pressure dropping to 0
ANSWER : Your vehicle has a fair amount of miles on it, but the pressure reading should still come up when you are driving. With a new pressure sending unit and a new oil pump, there must be a blockage inside the engine or there may be a disturbed bearing that isn’t allowing oil to flow properly. Consider hiring a technician to check the actual mechanical oil pressure at the sending unit port and again at the oil filter. The same technician can check the knock sensors to see if the sensors are faulty or if they are going crazy because of an internal engine concern. Consult your nearest machine shop or engine repair facility.

When I come to a stop sign the oil light pops on and the car feels like it is going to stall
ANSWER : Hi There,
It sounds like you may have a dirty or faulty idle air control valve that may causing the fluctuation in your idle at stops. As a result of the low idle, the oil pressure will also drop since the oil pressure sensor is designed to pick up a specific amount of oil pressure based upon normal idle RPM’s when at idle. I would suggest testing the idle control valve to check resistance by doing the followng: disconnect the IAC valve, connect an ohmmeter to pins 2 and 3 of the valve. If you get a resistance value between 10-14 ohms, this indicates IAC valve is working as it should. Next, connect the ohmmeter to pins 1 and 2. If you do not get a resistance value between 10-14 ohms, the IAC valve may need to be replaced. If you need further help with this, please do not hesitate to contact us here at YourMechanic as we are always here to help.

Are there accurate electrical oil pressure gauges that will beep me when my oil pressure goes too low and how do they work?
ANSWER : Oil pressure reporting systems with programmable audible alarms are readily available. An example is the CruzPro Digital Gauge but there are many other vendors and you really have to do a product comparison and look at all the reviews. Once you select an audible alarm based system, if you desire a professional installation, you can use YourMechanic’s oil pressure sending unit service page to request installation. Of note, most damage to engines related to oil starvation occurs in the few seconds after starting. Therefore, I would recommend you FIRST install a pre-pressurization system as that will give you the most bang for the buck and indeed solve what is an immediate problem in all engines. An example of this product is the Insta-Lube Engine Pre-Lube Kit. Again, though, there are many variations on this solution. I highly recommend pre-lube and the only reason all engines do not have it is such a system adds cost and complexity to motor vehicles but it solves a real problem. A certified mechanic from YourMechanic can install such a pre-lube kit as well, if you desire. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

replace oil pump and pick up tube
ANSWER : Hi there. Typically when the oil pressure changes based on the type of oil you are using, it’s an issue with the pick-up itself. Quite often, the wrong sized or style of oil pump or a pick-up line that is too short / long, can cause inconsistent oil pressure. It’s also possible as you indicated that the oil pickup screen is clogged with sludge or debris (especially if the engine has not been rebuilt). It might be a good idea to have a professional mobile mechanic complete an oil pressure light inspection to help you pinpoint the source of the issue and recommend the right repairs.