My truck has been going with the flow of the weather, when it's hot it's gets to 220+, and when it's cold I'm lucky if I ever make it to 165/170. So I switched thermostats a year back, still the samething, I put in a bigger radiator and now it doesn't get so hot, I also switched thermostats agian after I did that, still no change during this winter, I had the radiator almost completely covered to get it to 170 in the winter, now with the bigger rad it runs 190-200 unless I'm sitting in traffic for a longtime on a 100 degree day. I can't figure out what this things deal is, if the water pump was junk it should heat up in the winter to, but no go there. It's been doing this ever since I rebuilt it 3 to 4 yrs ago. Has anybody ever had this issue? It's like it's bypassing the thermostat somewhere.

 

Are you using a fan shroud?

 

Just the top part, but that's whats always been on there.

 

If it's the factory shroud, it should be good enough. My '79 actually didn't even come with one. The inline sixes don't demand too much cooling power. What are you using to monitor the temperature? If this is an electrical gauge, you should replace the sending unit and check the wiring. If this is a mechanical gauge, you should inspect the metal line for sharp bends or kinks, which can alter the reading.

If you're absolutely sure that the numbers you are seeing are true, you'll just have to go through the basics. What thermostat temp. are you using? 190-195 degrees is what you want. Many people say to go with lower ones but that is actually bad for the engine. Running at a cooler temperature actually increases bearing wear by a large factor. Make sure the thermostat is sitting the correct direction. Make sure the fan belt is in good shape and properly tensioned. Flush the cooling system. If this is a high mileage engine, a new water pump wouldn't be a bad idea. I flushed the block on my truck one time, with the original water pump. A while later, I replaced the original water pump because I was changing to an electric fan setup and thought I'd replace the pump while I was in there, for good measure (30 years old). I took a look inside the pump and was amazed at the build-up inside, even after flushing the system. Some of that stuff just doesn't want to come out. Is this a flex fan or a clutch fan? If it's a clutch fan, inspect it.

You'll just have to go through each basic component of the cooling system and make sure it's in proper working order, or replace it if there is any question. Luckily, most of the cooling system is pretty cheap to replace. The only exception is the radiator ($$$) but you've already replaced that, so the expensive part is over. Like I said before, the 300 doesn't need much to stay cool.

 

Well, when I rebuilt the engine I had put on a new water pump, and like I said ever sense I rebuilt it I had this problem. I am using a 190-195 degree thermostat, on my second one, it's in the right direction, I flushed the system when I changed the rad. It has a fan clutch, it seems to work well enough and if it didn't it should heat up in the winter, not stay even cooler. I'm using a mechanical guage, but I can tell it's right by the way the heater works (like crap) although the heater core could be replaced it was startin to leak at one time and slipped some stop leak in it and it took care of it, but otherwise if I cover up the rad. in the winter I can get the heater hot enough to barely keep the windows defrosted....barely. But hot in the summer, cold in the winter, sounds like a stuck open thermostat right? Or at least a systom of it.

 

Sure does. The only other thing I could think of would be the stop-leak messing it up. The problem with that stuff is it works a little too well. If it can clog a leak in your heater core, just think what else it can get itself stuck into. Not really sure what else could be going on; from what you're saying it sounds like you had the problem before the stop leak.

How old is your radiator cap? Did you replace it along with the radiator? If not, you should.

 

Yeah, I did put the stop leak in while the problem already exsisted. Yeah the rad. cap was new with the radiator. I had also flushed it after the the stop leak (stop leak was b4 the rad.) and was afriad I'd wash it all out and my heater core would leak agian, but even after back flushing the core both ways it did ok this winter, well summer to, they just usually go out in the winter since that's when you actually need the heater, lol. You wanna know the bad thing? I'm an Auto Tech myself and can't figure this stupid thing out, but then agian the 2 other guys at work couldn't think of any reason either, so I was hopeing were all idiots and we were missing something, lol. But I am with you on the stop leak, that stuff can get you in some trouble if you go overboard on it, I really didn't put that much in, just enough to remedy the problem at the time (headin back home in the winter a few years ago) and it took care of it ever sense.