If this issue has been addressed before please forgive, I did a search and found nothing pertaining to my specific situation so I'm hoping I can obtain some assistance. My 2000 Plymouth Neon has 181,000 miles on it and for nearly two years I have been battling an overheating problem during the summer months (I live in south GA, it get's a little hot down here). When the ambient temperature reaches 80F degrees or above and I'm on the interstate running about 70-75 MPH my temp gauge will start to soar past the 3/4 mark and it doesn't matter if I'm running the air or not, of course running the air causes it to rise faster and then the air cuts off, slower speeds the temp only rises just a little past the half-way mark. Okay here is a list of things I've done so far and none of them have been successful: Radiator cap, thermostat, radiator flow tested and cleaned out (was 20% blocked), new timing belt, new drive belts, new water pump and I did have Bosch platinum plugs in there - I just took those out a couple of days ago and replaced them with Champion with Autolite plug wires which leads me to another problem that I encountered while taking out the plugs, plugs 1-3 were coated in oil but number 4 was dry and clean. I called a friend of mine that is a very good "backyard" mechanic and he told me the head gasket was blown which would account for my overheating issue. Does this sound accurate? Keep in mind I have owned this car since 2000, drove it off the lot with 7 miles on it and it is my understanding that with a blown head gasket you would notice a substantial loss in compression leading to loss of performance, more oil usage , oil in the coolant, ect ect but I have not notice anything of the sort so I'm wondering if the head gasket is the way to go - according to the book, it's a very time consuming difficult task! I can't afford anymore mechanics shops telling me there's nothing more they can do. Thank you in advance for any assistance and sorry for the book.

 

Overheating issues are most commonly caused by some sort of leak. A faulty water pump will occasionally pop up. So it sounds like you've taken the right steps in troubleshooting so far.

Is it actually alarming for high temp, or just higher than you would like? The water temp sensor is a two-part deal - the accurate part goes to your PCM where it is used for fuel trim, fan operation, etc. The idiot portion goes to the instrument cluster and is a rough guide at best. I'd put it a step ahead of the oil pressure light as far as usefulness... Do you have the means to datalog the actual sensor data (OBD-2 scanner)?

Oil in the spark plug tubes on SOHC Neons is usually caused by leaky seals. The tubes are set in seals attached to the valve cover. Nothing from a head gasket leak would automatically cause oil in the spark plug tubes in our cars. We are not Ford.

A compression test and leak-down test on your car should show the presence of a head gasket leak. This is something your mechanic friend should be able to do with basic equipment (air compressor required). A shop can do it, but you'll probably pay $50-100 for their time. If you have an air compressor yourself, the parts you need only cost $20-30 at most parts stores (fittings, hoses, and gauge) and are usually availables as a set.

My overheating has always been pinned down to either the rad cap or pinhole leads from the radiator itself. I went through the stock rad and 2 replacements in 215,000 miles or so living in New England. I finally got an aluminum core (less than a copper core from Autozone), and I'll never have to worry about corrosion again.

Best of luck!