QuestionMy 2001 300M tends to run hot, much hotter than before the transmission shredded itself 3 years ago. I've had the radiator, radiator overflow tank and cap replaced. It's now running about 3/4 guage hot without overheating but it's concerning me. The floor boards are always hot too. Is that normal? No one's mentioned it in the passenger side but the driver's side is hot.
AnswerHi Vicki,
I have a couple of ideas. First have you tried changine the thermostat in the engine? That might be sticking partially ajar instead of opening all the way. Another possibility is that the temp gauge is not reading accurately. Does the radiator itself seem quite hot or threaten to bubble steam out of the overflow tank? If not, then the cooling system may acturally be OK and the gauge is just pessimistic. If you have a good thermometer try putting it in contact with the metal piece where the upper radiator hose joins to the engine and see what it reads when the gauge is at 3/4. 3/4 scale is 'high normal' and so long as it doesn't push into "H" it in not a cause for alarm.
The floor board heating up is probably due to the catalytic converter that carries exhauxt gas being located just below the hot spot. There is another one positioned similarly on the passenger side. That may be normal or it may be partially blocked, or mounted too close to the floor board. An independent exhaust shop could be asked to look into it, and they can be tested for proper function. These devices get quite hot normally. If the passenger side doesn't get hot in the same area that would suggest a reason to have a look at it.
It also may be the case that there is an abnormality in the functioning of the engine which results in excessive heat in the exhaust system. The best way to check for that possibility is to see if the engine control computer has noticed a problem and encoded the issue as a 4-digit fault code number stored in its memory. Turn the igniton key:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the odometer window to see if the mileage reading changes to show instead a 4-digit number preceded by a P. If so, let me know what it is and we'll go from there.
Roland
PS Thanks for the rating. On the 3.5L engine the thermostat housing is low on the engine so he will have to jack up the front wheel to get to it. The lower radioator hose goes to the thermostat housing. He will want to drain and collect the coolant to start with. Disconnect the oil pressure and power steering pump pressure switch electrical plugs. Then remove the hoses at the housing and finally the housing. When refilling the system use the bleed valve located to the left of center on the lower intake manifold and attach a hose there to and run it to a collection container. Then pinch the hose that connects the two parts of the coolant bottle and add coolant only to the smaller (inboard) side of the bottle (there is a special funnel for that, part no. 8195 but you can improvise I believe). Add through the funnel until coolant starts flowing freely out bleed valve hose into the collection container. Then close bleed valve and fill bottle to mark. Remove pinch clip from hose. I hope this helps.
Do consider the possibility that the gauge may be be falsely reading high, however. If the needle doesn't typically move about that point it would be considered within the normal range of operation (1/4-3/4 scale, varying). You might be unnecessarily opening a can of worms if the thermostat were actually OK.
