car isnt over heating, but the temp fluxuates between normal and almost overheating. the temp gauge, will be in the middle, and then all the sudden itll rise almost to the top. the fans kick on and it drops the temp, but it worries me, ive never had a car do that before to me. ive replaced the thermostat and the gasket, put a new radiator cap on, put a bigger radiator in, and changed out the water pump when i did the timing belt. I think it may be a sensor or something. just wondering if anyone's had this prob and they fixed it. any assistance wud be apreciated.

Thats probably nothing to worry about but have you checked your oil. If it rises that quick you may have some friction in the engine some where. I had a 65 mustang once in my life (I miss it) that did that when it wasn't circulating oil (distributor ran the oil pump and twisted in 2). Other than that its probably normal.

I was having almost the same problem and one of my heater hoses had a hole in it. You should check that and your coolant level. Make sure it's full.

Does your heater ever stop working or blow colder?
(If so, you have air in the lines.)

Take off the radiator cap with the car COLD and the fluid level should be right at the top, against the cap.
(If not, you have air in the lines. Refill, and continue refilling daily (2-3 days max) with the engine cold until it stays full.)

You could try bypassing the heater core, connect both lines at the firewall to eachother using a 2" piece of pipe.

Pay attention to the oil next time you change it, you should have slightly less than you put in originally.
(If you have more, it's a leaking headgasket.)

If you have white smoke out the tailpipe once the car has warmed up for 10 minutes (and its not 40 degrees outside) then its the headgasket.

If you have a small oil leak down the back of the engine between the head and the block. Use a flashlight, get under the car, and look carefully in the space between the engine and the firewall.
(If you have a leak there, its the headgasket.)

If your coolant level is staying the same, and the oil level is staying the same, and there are no white deposits on any cooling lines indicating a leak, then it's probably the headgasket.


Anyways, you correctly replaced the obvious things. Really the only thing left IMO is the heater core leaking/blocked or the headgasket.

preciate the help guys. ill try all that. but im starting to think its the head gasket. i bought one the other day. ill try and put it on. is there anyplace i can go on the web to see how its done on the 420a.

Originally posted by stevenutz
preciate the help guys. ill try all that. but im starting to think its the head gasket. i bought one the other day. ill try and put it on. is there anyplace i can go on the web to see how its done on the 420a.

You can look for locked posts in this forum by DarkOne. He has a link to the FSM in his sig. Shows you how to remove everything and all that. Valuable resource if ever there was one, but I'm more inclined to say it's heater hoses. I had a leak in mine and that temp gauge thing was exactly what it did to me. It goes hot from steam being introduced in the system (as there is air at that point), as this steam passes the temp sensor, the gauge reads hot and the ECU turns the fans on. Once the coolant gets pumped back by the sensors, it cools back down. When it gets hot like that again, crank the heater and make sure you're getting hot air air from the vents. If not, start with the simplest plan of action.

This is what happened to me.

The wires to the fans got severed so my radiator was not doing the job right. I overheated and I fucked up the headgasket and warped mi head slightly.

I would idle and drop gallons of coolant on the floor withour noticing. I then drove and the temp just spiked to full overheat in a second. Since I dropped some coolant, there was now air in the system. I changed the thermostat, the hoses, and it came down to the headgasket.

I am experiencing something similar in a way. Last weekend I was driving home and the temp went up almost to the top , I noticed there was smoke coming under the hood and coolant smell. I got home looked around and noticed a small crack on the upper radiator hose from which coolant was leaking. I ended up replacing the hose, filled up the radiator with coolant. Now I can drive on the highway with no problem, even stop at a light and at regular street speeds without much of an issue. However at certain random points, the gauge will raise from the middle to more or less 3/4. I've noticed it has done it a couple of times when I 've accelerated a bit hard from a dead stop, or if im making a tight turn like going up a garage ramp sometimes it'll do it as well. It'll eventually go back down on its own, although usually i'll try to let off the gass when i see it happen. I also hear water noise when i start the car and also while driving if i listen close enough. Wondering if air trapped could cause this overheat at only certain periods? I've changed the radiator cap, upper hose, and recently water pump with the timing belt. I can't really see any more leaks either.