2003 Dodge Intrepid Possibly a head Gasket issue?

did the knocking happen after they worked on it? was it hot when it was knocking? does it do it all the time or t just happen that one time and thats been it?

symptoms sounds like it could be a issue with the head gasket. a compression test performed on the cylinders will either verify that or tell you to look elsewhere. how long does it take to overheat

The knocking occurred twice only. When I turned it on today there was no knocking, or rough idling etc. The knocking did occur when the engine was hot on the weekend, but not today.

It takes about 10 mins to overheat. When I pulled up at work today (5.5 miles from the garage/10 mins) the engine coolant warning light was on. When I turned off the car, I could hear what sounded like the coolant area percolating/gurgling. I let it sit for several hours before driving it to home. The temperature gauge was rising, but again no knocking, rough idling or gurgling sound occurred.

The garage informed me that when they took it for a drive today it went very hot, then started to go back down over the course of a 10 mile drive.

This may or may not be relevant, but I noticed in the last week, my mileage per gallon dropped down about 20% compared with normal driving. One other thing, I live 6300ft above sea level in the mountains, not sure if that's relevant, but just thinking of what may assist in diagnosis.

Thanks

dropped 20percent. wow! sounds like it may be a issue with the ignition and fuel system!

try running a higher octane gas. also make sure the spark plugs are in good condition and gapped properly and ohm the spark plug wires. should be 7000 ohms per foot of wire

I have some more information to assist in possible issue.

I had a friend remove the thermostat, and inspect it, and it appeared fine. He then let the car remain in park and leave the engine running, to see if the two fans were operating as normal. They were, and eventually the cable started to get hot as he said probably would if the thermostat was operating normally. During this time, the car in idle was fine, and the temperature remained even where it always sits.

He then took the car for a drive less than a mile from the house, and the temperature shot right up near the redline again. He put the car back in park, leaving the engine running, and the temperature dropped back down to it's regular level. Leaving it for about 30 mins he did another test drive again, and the engine temp shot right back up, repeated the same procedure, leaving in park with the engine running, and the temp dropped back down.

Does this give you a better idea? He seemed to think if it was a head gasket issue, it probably wouldn't drop temp wise, while the car is running. He thought perhaps it is a line or something connected with the transmission that only effects the car when driving?

wouldnt think its transmission issue. is the rpms staying the same as they normally are when driving or do they seem abnormally high.

it could be due to the fact then when driving the vehicle does have quite a bit more load on it causing it to run warmer. so its not thermostat or fan related.

Has the cooling system been flushed out and refilled with clean coolant and water?

i want you to test water pump also. with the thermostat out and engien cold take and hold the upper hose shut. do you notice pressure build? when released do you feel a surge of water go bye or nothing?

with drivebelt off does car heat up just as fast?