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Running HOT!!!!!!!!

H

Hoover87

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Hello once again,

I finally got the GM 350 H.O. into my old 305 TBI truck. It started right up first turn of the key. Still have some fine tunning to do, but it wants to go!

One problem...anything more than an idle and it gets HOT! Average temp going down the road at 2500 RPM is a bit over 210. If the RPM gets any higher the temp immediatley jumps up...sometimes close to the red. If I let it sit and idle it will stay right around 190 all day. It has a 190 degree thermostat. I cheked to make sure the thermostat was not upside down and its not...I turned it over anyway just for the heck of it and no change. The next thing I will try is to take the thermostat completely out.

Any ideas????????????????

Thanks,

Mike
 
only thing i can think is plugged heater core, plugged radiator, or the head bolts are lose and need tightened down and therefor the heads are sucking air. is your fan shroud intact ? do you have a lift and your shroud is not centered on the radiator ? is your fan clutch working ? let us know please if you come up with an answer.
 
You might want to take a look at your radiator, it may be too small for the 350. I put a GM ZZ4 350 in place of a 305 in my dad's truck and we had to get a larger radiator. I believe the original one in his truck was only 2 rows. Now it has a 4 row and you can't get it to run hot now. /forums/images/icons/wink.gif
 
Good stuff guys. Well, the heater core is good I think because I turn the heat on high to help cool the engine and darn near cook myself to death. That water pump is brand new and with the radiator cap off I can see water flowing from the heater hoses and levels change with high/low RPMS.

Plugged radiator, hmmm, it worked okay with the 305 but I will give it a look. Head bolts is another interesting idea I may look at. Another post I read mentioned mis-adjusted valves causing it to run a little warm.

I will probably end up going to a larger radiator, but this thing really heats up quick when you start going down the road. Anything over 2500 and it looks like it is gonna burn up. I also have a fear that it might be running a bit lean, would a lean condition make everything heat up as soon as you start driving it?

Mike
 
A lean condition can definetly cause it to over heat, if it's bad enough it will happen very quickly like you're describing.

Timing can also cause this.
 
could be from a Small whole in the Rad. Check that out. Mine was doing that about a year ago. I put a new rad. in, new Cap, Flushed the block, and temp gauge. I have head of guys having an Air pocket at the temp gauge, that that was causing bad readings at the temp pick up. just some ideas. do not for get, if you have a auto tranny, you might be making more heat with the MORE power from the new motor. There could be some slipping at the Tor/Conv. and that is causing more heat at High way speed.
 
Its a 4-speed manual. I'm going to pop the thermostat out before I drive home tonight and see what happens.
 
Your stock radiator is sized to cool an engine that made about 180 HP. It's also old and most likely has a lot of scale, corrosion, etc. inside that reduces its cooling ability. Now you have a 330 HP engine under the hood. To make more power, the engine has to generate more heat. That heat needs to go somewhere!

Check out www.radiator.com. They have great deals on radiators. Too bad you haven't coughed up the $25 to be a CK5 member yet. With the CK5 member number they'll also give you a 10% discount. /forums/images/icons/cool.gif
 
Be careful of running without a thermostat. Without one it's possible for it to overheat even worse because the water passes through the rad too fast to cool down.
 
Do you have the correct water pump (clockwise versus counterclockwise rotation)? I believe the old v-belt style was clockwise and the new serpentine belt style is counterclockwise but I am not 100% sure. I do know one is differnt than the other. Many people ask for a SBC waterpump and the parts store will give them an older style v-belt pump, but since you have TBI I assume you have the new Serpentine belt setup. The trouble with trucks around 87 and 88 (maybe higher) is that some TBI motors came stock with v-belts and some came stock with Serpentine belts, so getting the correct water pump is not always easy (especially with some of the monkeys they have behind the counter....disclaimer* not ALL parts counter attendants are monkeys, I know a few that have their $hit together). Both pumps look identical and have identical bolt patterns. At low rpms they tend to stay cool if you have them mismatched, but at higher RPM's they can't circulate the fluid as it should be and it will cause it to overheat. As stated too, bad valve adjustment, lean carb settings, and/or poor ignition time can cause high heat. If your exhaust pipes start glowing you will know /forums/images/icons/confused.gif The only reason I don't think it's timing is because if the timing is off, it usually will affect idle temps as well but not always so who knows. Let us know how you make out.
 
If you have a local radiator shop, see if they will flow test your radiator for free. If the thermostat is the sole problem, obviously removing it will completely eliminate the problem. At cruise your water pump should be moving a lot of water, (higher RPM's than idle) so that shouldn't be an issue.

I went to a bigger motor on a corroded radiator, and it wouldn't even idle without overheating, but a flow test confirmed it was corroded pretty heavily. The cores I could see inside looked good, but more than likely the lower ones were all corroded.

You can't move water too fast in these cooling systems, so thats not going to be an issue. Water can only absorb so much heat before boiling, and moving a lot of cold water past something and cooling that "smaller" amount of heat works better than letting it sit in place, get as hot as possible, then trying to cool that. The thermostat shouldn't be opening/closing fully all the time (or you'll see engine temp spikes with a constant load) it should be only closing or opening enough to maintain 195*

Replacing the radiator without knowing it to be the problem is costly, thus why I suggest a flow test if removing the t-stat doesn't solve the problem. A sticky t-stat can easily cause overheating or temperature spikes.
 
1st thing I would do is pressure test the radiator cap, or replace it. If the cap doesn't hold pressure it can run hot or even over heat. I agree with nvrenuf, I wouldn't run it without a thermostat, the water travel through the radiator too quickly and will not have a chance to cool. Retarded timing can also cause it to run hot. You can never go wrong with a 4 row radiator.
 
That is simply not true. I can take the thermostat out of mine and run at 100* all day long if I wanted to. Moving more water, faster, will only increase the cooling capability. (which is what happens by removing the thermostat) Of course, thats assuming the radiator isn't trash.
 
It is possible for the water to pass through the rad without significantly dropping in temperature, especially if the truck is originally equipped with a small rad (remember, the truck in question is a 305 truck). The amount of time the water spends in the rad directly effects the amount of heat it can dissipate (lowering the temp). If a thermostat was an unnecessary part, every car manufacturer would not be using them.
 
Remove t-stat, stick a hose in the radiator, turn it on, and run the vehicle. Tell me if it overheats.
 
I agree. In my experience, nothing can overheat without a thermostat. Mine would never even get to operating temperature.

I have heard that sometimes it doesn't work that way though because laminar flow isn't turbulant enough to dissipate the heat, but in actual practice, I've found that it's simply not the case.
 
If your radiator sucks, then no, you won't be able to keep it cool no matter what. (except the hose example)

The real problem with keeping the coolant in the radiator longer, is that block temps increase the longer you keep the water in the radiator, which leads to boiling around the cylinders, which equals lessened heat transfer to the coolant. The radiator can only "dissipate" so much heat, (based on surface area, construction material, airflow, coolant movement, etc) and the higher the *incoming* coolant temp, the less effective the radiator will be.

I had a GM V8 that I could stick my finger in the coolant after running for an hour, because the PO's didn't feel a t-stat necessary. I thought the gauge was bad until I popped the cap lol.
 
here is my 2 cents you spent alot of $$$ on your 350 HO spend a little more on a nice new 4 core radiator when i did my swap new radiator was one of the first things i bought? a 165 thermostat was the next thing, new water pump? it's like buying a $500.00 dollar suit and wearing dirty underware? just basic upgrades in my previous profession i was a marine mechanic any motor job i did i required new water pumps ,circulating pumps and manifolds if you didn't buy these parts you didn't get a warrenty??when your far from home those new parts you will buy will give you piece of mind??? /forums/images/icons/wink.gif ps my draws are useually clean good luck.
 
The way I look at it is, my motor is going to cost me around $3000 all said and done. Another $100 out of my pocket for a part that might be good, and can be tested to verify if it is or not, is money taken away from some part that I *know* needs replacing.

You don't throw your underwear away rather than washing them do you? /forums/images/icons/smile.gif
 
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