My 300 has been overheating a bit since I bought it.So yesterday,I went by Auto Zone and picked up the coolest thermostat that they had and installed it last night.It's temp range is 160.Anyway,the coolant and everything looked great and it tested excellently also in my antifreeze tester.It was nice and clean.

But my problem was this with the original thermostat.It was a 180 and the temp gauge wanted to run about 3/4 of the way over.Sometimes it would be just shy of that little mark right before the 'H'.Anyway,I put this thermostat in and let it idle for an hour last night with the A/C on high.I rarely ever touched the gas pedal.It ran about halfway or just a little bit past the halfway mark.I thought...That'll work.When I'm driving down the road,it'll cool down...

WRONG!!

I was driving home today and looked down at the gauge.It was running in the same area as it did with the 180 thermostat.This is with the A/C going and everything.This is really starting to worry me.I'm supposed to be towing a 1975 Plymouth Valiant with it next weekend,but if I can't get this straightened out,I'll burn it up when I'm towing that car.

I want to say that it's either clogged or it's the transmission.It's an automatic and I want to say that it's the C4.It's just too wierd...It runs hotter when I'm driving down the road.Doesn't that point to the transmission?

I'm going to try one more thing.I'm taking the thermostat out tomorrow and I'm going to see if it still runs hot.If it does without any thermostat at all,someting is definitely wrong.If it does,I'm taking it to a shop to have the cooling system flushed with one of those machines made to do the job.If it still overheats after it's been flushed and with no thermostat,it's going to have to be looked into.But,before anything serious happens,I'm going to check the accuracy of the gauge and the sending unit.Hopefully the problem will be with those two pieces of equipment if the thermostat removal or the cooling system flush doesn't do the trick.

Any insight on this problem is much appreciated.I'm going to have to disect this thing until I find the root of the problem.But,I have a bad feeling that it's something to do with the transmission.

Nightrain

 

I doubt if your overheating problem is transmission related. The most likely causes are a partially clogged or damaged radiator, a water pump that is marginal, bad thermostat, or bad temperature sensor.

The cooling system flush is a good first step. After the flush, run the engine at idle with the radiator cap removed and verify that the thermostat opens and you can see flow through the radiator. Check your temperature indicator - it should read low or low normal in this condition.

Put the radiator cap on and run the truck. If the temperature goes up toward overheating while driving, the radiator is suspect.

Lou Braun

 

Thanks Lou.I'll check that out.

I had the cap off yesterday right after I put the new thermostat in and I noticed that the coolant level did drop.I want to say that the radiator was left about half full.That's what it looked like from where I was standing anyway.The coolant level came back up a few minutes later.So,the water has to be circulating.

My dad is off tomorrow and he agreed to come over and lend a hand while I redo this again.I picked up a bottle of radiator flush at Auto Zone a few minutes ago,so I guess I'm gonna go ahead and flush the system and replenish it with new antifreeze and no thermostat.

So,afterall my transmission isn't messed up?It hasn't been acting weird or anything,so I wasn't sure if it was the culprit or not.The worst that it's looking like now is the radiator.That's no big deal.

Thanks for your help once again.

Nightrain

 

If you feel the parts *might* be marginal, it's best to replace them all and be 100% sure that they are all good.

My recommendation is to have the radiator serviced (at least remove it and have a shop look at it), change all your hoses if you have never done so (including the heater hoses), and while you have the radiator out replace the water pump. Yeah, it'll run you a few hundred bux all-told, but it'll be cheaper than towing you and your Valiant back home from the boonies, and you'll be able to drive around with confidence in your cooling system.

That's my recommendation...

Dan Martin
1986 F350 Crewcab Dually, 460, C6.

 

Thanks for the advice Dan.I believe that I'll hold off for a little while on the pump and all.I just spent $500 on this truck in the shop and I don't really feel that the pump is bad.The radiator might need to be looked at though.After my work is done tomorrow and if it still overheats,I'm going to have to do something.

BTW,if it still overheats or I feel that I'll have problems with the cooling system while towing,I'm not gonna be pulling that Valiant .

Nightrain

 

I say throw a real guage in there and see what is really going on.
The factory guages should be expected to be inaccurate in these trucks, the instrument cluster voltage regulator is likley hurting...

 

I agree on the gauges,but I can tell that this engine is overheating.I can pop the hood after a long run and grab onto one of the heater or radiator hoses.It'll almost scald the crap out of my hand.You can feel the heat coming off the engine.It's obvious that it's overheating.

Tomorrow is lurking closer and I can't wait to get this big 'ol gal back on the right track.

Thanks for the advice once again.

Nightrain

 

I agree on the gauges,but I can tell that this engine is overheating.I can pop the hood after a long run and grab onto one of the heater or radiator hoses.It'll almost scald the crap out of my hand.You can feel the heat coming off the engine.It's obvious that it's overheating.

WHAT????????
At any temp over 140 (that's less than the 160 deg you installed) you should get scalded! And if its "over heating", not just running hot which is what happens when an engine is worked, there should be steam blowing out the radiator cap vent.
I forget what the ratio is but with an 18 lb cap on the radiator, 220 deg would not (boil) over heat it or be out of the question for a 190 thermostat and a truck running hard, fast or pulling a trailer.

Those senders and gauges can be off quite a lot, normal could be near the "C" or the "H" or anywhere in between, and if that is where 180/190 deg is on yours (normal) then that's where it is.

Put a temp gauge (little gauge with a small rod sticking out the bottom with a range of 0 to at least 220) in the radiator water and see what temp it is when you think it's hot.

Start there and verify the problem before you throw money at it.

Then again, come over here and I'll sell you a new radiator, hoses, thermostat, sender, gauge, heater core, water pump and fan clutch.

And never run without a thermostat, ever, it's there for a reason, a good one.

 

b4 I got mine, it must have been overheated since the former owner took out the thermostat (I was wondering why it would'nt get above 140 on a 30 degree day).

I drained the coolant, and discovered the bottom of the rad was so plugged i couldn't use the petcock to drain it, so off came the lower rad hose. a lot of brown looking fluid and yucky stuff came out, and I put it back together and run it.. On an 85 degree day, it will stay between 205 and 210. That is good enough for now. I haven't towed with it (have other things to worry about aside from over heating, like the mains falling out, oil pressure, blah blah, the rear bumper falling off, yadda yadda yadda).

so, at least try changing the fluid, and getting a mechanical gauge. That makes the difference.

 

Thanks fellas.

So are ya'll suggesting not to run without a thermostat?I'm just curious because this is what the guy at the parts store reccomended.I understand the principles of a cooling system,but I just don't really know how to go about working on it.

Nightrain

 

Always run with a thermostat! The water pump is a standard centrifugal pump and is designed to run against a certain backpressure. That backpressure (or pressure restriction) is provided by the narrow passage through the thermostat. If you remove the thermostat, you would need to install the correct size restrictor orifice in place of the thermostat.

When a centrifugal pump is run with very low backpressure, it can stop pumping coolant and will cavitate. Engine overheating would result. The problem would get worse with higher pump (engine) speeds so things might look OK at idle speed but you would see overheating at highway speeds.

Lou Braun

 

not to mention that accelorated engine were will occur when the water is under about 150 degrees.

 

Okay,the thermostat stays .It's too much of a risk to remove it.

I wasn't able to get done what I wanted to today,but I did get something else that's very important covered.

I stopped by Auto Zone this afternoon and picked up a temp sending unit.I finally got around to installing in at about 10:00 tonight lol.After I got it in,I started the truck and let the choke kick in.I started it at 10:00 and ran it until 10:05 when I hit the gas and cut the choke out.I then let it run at idle until 10:15.At this time,the gauge is reading 1/4 of the way.That's about where I want it.Right at 10:15,I kick the A/C and fan on high.I run it like that until 10:20.When I stopped it,it was at 1/2 way.Is that about right?It's 66*F with the humidity at 87%.

The only reason that I stopped it when I did is because I noticed that I sprung a leak.The top heater hose which is the highest on the thermostat housing started leaking.No big deal.I did it when I was installing that sending unit,but I didn't notice it until the truck ran for awhile.I figured that I would quit my test for the night and start again tomorrow.

I'm going tomorrow and get two gallons of antifreeze,some type of cooling system flush,and two new heater core hoses.I'm going to go ahead and replace both heater core hoses while I'm at it.I'm also going to flush the system tomorrow.I think that Prestone makes some type of cooling system flush that you run with water in the system for so long.Is this correct?I think that my buddy at Auto Zone told me to replenish the system with two gallons of antifreeze and fill the rest with water.Is this correct also?If not,what is?

Maybe by tomorrow I'll be back on track.

Nightrain

 

just to mention check to see if you have air trapped in the manifold where the sender is

 

Which sender did you replace? If the truck has a computer controlled ignition system, you have 2, one on the thermostat housing, which is for the computer, and the other, for the guage, which is located under the rearmost runner of the intake manifold.
Either way, a new sender will only help a factory guage so much. A good mechanical guage in the stock guage sending unit location is best.