Same problem on my Dodge van, Can anyone answer the question without giving me safety tips about it? Its overheating when the cap is on.. So doing possible engine damage.. Can someone tell me why its doing this?

Does it go down after a drive or when it sits overnight?

If it goes down after a drive, you may be leaking coolant into the combustion chamber. If it does down overnight, you’re probably leaking it onto the ground somewhere. You should be able to narrow down the leak using your nose (the coolant smell will be stronger near the leak), or look for white streaks around the cooling components. You may also notice a little puddle under the vehicle or a stain where it dried up.

They also make UV dye you can put into the coolant to help you track down leaks with a black light.

The radiator cap is what holds the pressure and increases the boiling point of the system. This is important for proper function of the cooling system. It’s also dangerous to leave the cap loose because there is risk of the hot coolant burning you, so I highly recommend taking the vehicle to a shop to get checked out and repaired. If you’d like to try a few more things yourself, check out this article: http://cartreatments.com/causes-and-symptoms-of-engine-overheat/.

You may also want to perform a leak down test. This will tell you for sure if there is any air from the combustion chamber that is making its way into the cooling system. Black/blue smoke is a sign of oil burning, not coolant. Coolant smoke is white and sweet smelling.

Hey there, don’t panic. There are a lot of things that could go wrong with the cooling system and they can be difficult to pin point. However, follow these steps to find the actual cause of your cooling system malfunction;

1. Make sure you use an original new Jeep radiator cap. They are cheap and could simply be the root of your problem. Using general or aftermarket caps could result in a lot of problems, one being the coolant easily boiling and creating vapors that seriously reduce the effectiveness of your cooling system. Your car is 30 years old, it’s likely due for a new original cap.

2. Make sure you have no leaks. Check the hoses on top and the bottom, coolant turns white when it dries up, so it’s easier to identify. One or two hose(s) sit on top and run straight from the engine to the top of the radiator. Another hose or two hoses are at the bottom of the front engine bay run from the middle or bottom to the radiator. Rub your fingers along them and check if they’re dry. Check if you can see any cracks or perhaps small leaks. If so, you might simply lose coolant or introduce unwanted air in the cooling system. If so, replace the hoses or have someone replace them for you.

3. Let the car idle and set the AC to the coldest setting. If you don’t have AC, just wait for the car to warm up while idling and check if the radiator fans in the engine bay turn on. If not, they are likely the issue. The fans normally only work when the car needs extra cooling while driving and/or it’s not driving. While driving, the wind normally cools the radiator enough.

4. After testing the AC and fans, set the heater to maximum and check if you get steady hot air from your vents. If the air stays cold or if alternates between hot/warm and cold, your waterpump is likely malfunctioning and needs replacing. Repairing a waterpump is not really worth the effort, just have it replaced if needed.

5. Park the car at a slight incline with the parking brake on tight and let it cool down for 6 to 12 hours. When the car is cold, open the radiator cap and insert a funnel into the neck of the radiator. Wrap the neck of the funnel with tape until it is wide enough to sit tightly in the neck of the radiator. Also place an empty bucket near the radiator on the ground. Prepare a long screwdriver with a ball of tape on the end and test if it can plug the neck of the funnel. Fill a third of the funnel with fresh coolant and let it idle for a good 15-20 minutes to allow possible gasses and air bubbles to escape while coolant enters the system. After 15-20 minutes, no more bubbles should appear and you should plug the funnel with a long screwdriver with a ball of tape on the end. Safely remove the funnel with the hot coolant and drop it the bucket. Then close the radiator with the cap. Again, take precautions, coolant can be extremely hot and is a toxic mess!

6. Make sure your coolant is a bright color and very, very clean. No particles or oil should float in or on the coolant. If so, use a chemical coolant flush, rinse with demineralized water or if not possible just plain clean water. Then drain again and fill using a quality 50/50 premixed coolant. Make sure it’s replaced every 60.000 miles. If you have never replaced your coolant or use plain water as coolant, that is likely the source of the problem. Also, using old coolant or plain water will eventually block the radiator with rust and calcium deposits. A chemical flush will try to clean that up.

7. Step 6 requires you to flush the coolant system and then rinsing it with clean water. It is advisable to remove the thermostat in the process. Where the lower hose or hoses end and enter the engine, is where you will find the thermostat. You can easily undo the 2 or three bolts and remove the hose and remove the thermostat. Put the thermostat on a pan with hot boiling water and check if it opens. If not, replace it. Understand that the thermostat is a cheap part that is easily replaced. Instead of making a huge mess with coolant everywhere, why not replacing it anyway while you’re Flushing the system out with clean water?

If all these steps do not solve the issue, I fear that you might have a blown head gasket. Exhaust gasses are entering the coolant system and increasing the pressure, rendering it ineffective. I would advise you to do a CO2 test on the radiator then. You can find home kits for as little as 20 dollars online. Remove the radiator dap and place the tube on the radiator neck. Make sure it sits tight. Insert the blue fluid and let the engine run. If the fluid detects the presence of exhaust gasses in the coolant, it will turn green (small leak) or yellow (big leak). Please consult your local mechanic, he/she might already have a tester and could advise you on your options. Perhaps a new head gasket or just a sealer that might just do the trick? Head gasket replacements are quite expensive and a quality sealer might solve the from for less than a hundred bucks and keep the car running for a few more years. So no need to panic, you have options and ways to test what the problem is now.

Hope this helps, good luck!

Caution is advised, use water and heat resistant clothing and gloves. Also wear protective eyewear. Make sure you know how to open and close your radiator cap beforehand, coolant is highly toxic and can get dangerously hot. You don’t want to fiddle around with a cap and hot coolant in a hurry!

CO-test on radiator neck will detect the presence of CO gasses in the coolant while the car is running. And they can only get in the coolant by a blown head-gasket. Mayonaise-like or coffee with cream-like substance under your oil filler cap or on your oil-dipstick would likely be a leak of coolant in your oil. And white or black/blue smoke from the tailpipe would suggest either coolant or oil being burnt off in the cylinders. So yes, you can identify a blown head gasket without tearing the engine apart.

Make sure your cooling fans are plugged in and operational. Check the fan fuse – a blown fuse would prevent them from turning on, which could quickly overheat the vehicle if you’re not moving quickly.

Next, check your thermostat. If your thermostat is stuck closed, your vehicle will overheat very quickly because it is not able to get hot coolant out of the engine and pull the cooler stuff from the radiator.

You can easily test your thermostat by pulling it out and throwing it in a pan of boiling water. If it opens, it’s probably good.