About two months ago I hit a cow. It pushed the radiator back into the fan, cracking the back of the radiator. When the body shop fixed my truck, they replaced the radiator and fluid. Also the thermostat had to be replaced, it had stuck closed. Before that, the temp gauge, when the engine was fully warmed up, would stay almost exactly at the midway point. For the first few weeks after I had it fixed it was reading the same. But it's the middle of winter, and the temperature had been in the 40's and 50's. Last week it got into the 70's. I noticed that when full warmed up the needle would be just above the midway point. But when I got out, then got back in and restarted the engine, the needle would be 3/4ths of the way to the top of the gauge. When I would start driving again, the needle would go back down to the middle point of the gauge. I thought that the fan might not be working. But I checked it while the engine was running, and it was turning. So what could be the problem? I think that the body shop may not have mixed in enough water with the anti-freeze. But I'm not sure. Thanks for any help or ideas.

 

you may need to replace the waterpump, it could have been damaged upon impact and noone would have noticed it. also they could have put the wrong stat in the engine

 

If it's the waterpump, wouldn't it do it all the time? Is the fan supposed to continue running even after the engine is turned off? Until the engine cools to a certain point?

 

Our trucks have a belt-driven fan so it's not possible for it to run after the engine has been turned off.

 

I wasn't aware of that. I have had vehicles in the past had a fan that kept running until the engine cooled down to a certain level. What doesn't make sense to me is that the gauge will show it being hotter after I restart the truck than it was when I turned it off. I thought maybe the body shop didn't a 50/50 split of water and anti-freeze into the radiator. But I'm not sure.

 

So a damaged water pump? Could I tell by looking at it? Maybe a crack somewhere?
And if the stat was stuck closed, wouldn't it overheat all the time?

 

I would also check the clutch on the fan. The fan does spin all the time when the engine is running but the clutch free wheels most of the time when driving and when stopped in traffic the clutch does something to the fan. Not exactly sure how the clutch fan works but I think I'm in the ball park.

 

It is normal for a motor to increase in temp after shut down, that is why most cars with electric fans run them after shut down to help cool the motor. On none electric fan models, like ours, the water that is circulating through the block and normally cooled by the radiator is suddenly stopped from flowing and thus it cant disipate the heat from the block and heads. This is why you typically see a momentary increase in engine temp in warmer weather, especially if you restart shortly after shutdown. This should, however, be brief as the thermostat should be open and as soon as the motor is started the cooler water that was in the radiator should flow through the block and heads. In colder weather the cold ambient air helps cool the motor after shut down and minimizes (or eliminates)any heat build up.
As for why its running at a slightly warmer point than before:I agree that the clutch fan may havebeen damaged and is not functioning correct.They are designed to kick inat slower speeds and when the temp flowing over them from the radiator is hot enough. They should be thermally activated. So if the spring is damaged it may not kick in soon enogh. If, however, it is running warmer at speed on the road, you may have a little air in the system. Verify the proper fluid level and try bleeding the coolant system. A sticking thermostat usually will be very noticable. If your water pump is going out you would be able to feel movement in it when grabing the pully and trying to tilt it. Water pumps also have a small weap hole on the bottom that will be the firstindicators of pending failure, so look under the pump for any small amounts of radiator fluid.
Hope this helps, good luck