Heat issues

[davebloomer]

My 350 seems to be getting hot. When I am driving steady there is no problems. When I am setting at a red light with the AC on it will get up to 230 pretty quick. It normally runs around 195. Here's the kicker... when I turn the AC off the temp appears to go back to 195 in about 15 seconds... Does that seem possible?

Here's the equipment
Stock 350
165 degree thermostat (I should put a 190 in shouldn't I??)
Electric fan from a jeep grand cherokee ran off 185 degree thermostat and my in cab toggle switch..
And the AC of course...

So does anyone have any ideas or suggestions?

Thanks

Dave

[69GMCLonghorn]

You have to take the cooling system one piece at a time.

1) Start with the flow of coolant. Most people check the radiator first to make sure it's not plugged. This is a good idea and necessary, but you also have to make sure the BLOCK isn't plugged. Get it back flushed if you have a good shop in your area. This can help SO much I can't even tell you!

2) Check the water pump and make sure it didn't spin an impellor or is just plain going south.

3) That electric cooling fan. It wasn't designed for that vehicle so maybe it is not strong enough, maybe it is, who knows. Maybe it's a fan shroud issue... Oh and obviously, make sure it's turning on... duh!!!

4) Don't INCREASE the temp of the T-stat. Just get another GOOD 160° T-stat and install it, just to make sure it's not sticking, which it sounds like it could be. Cheap fix if that's what it is.

[mclairmo]

Make sure water pump pulley is smaller than crank pulley. Underdrive pulleys may cause low coolant flow issues. Also, make sure that the electric fan has a shroud covering the entire radiator core area. The fan needs to pull air in through the entire core, not just the round area where the round fan sits. Also, make sure that fan pulls enough CFM to cool your engine. Make sure wiring is big enough to feed it. Electric fans draw a lot of amps and need larger gauge wires. Try a high flow T-Stat and Water Wetter from Kragen or Autozone. Also, be sure that the fan is not pulling in hot air from the engine compartment through the radiator. Hot engine air sometimes travels under or over the radiator when truck is stopped and can get sucked back in through the radiator. You want only cool outside air going through the radiator. This is why many a/c equipped muscle cars had hood to core support seals to keep hot engine air away from the front of the radiator.

[cdowns]

sounds like the fan you're using is not adequate// maybe try a larger capacity fan or a 2fan setup

[cparman]

seems hard to believe that the temp would drop 30+ degrees in that short a period of time. I would suggest that you make sure that the engine is full of coolant, AFTER it has had time to completely cool down. Secondly I would verify that the temp gauges is telling you the truth. Third, I would keep the 160 thermostat. Does the A/C quit cooling when the engine heats up? I am thinking low coolant level, bad temp sender, MAYBE bad thermostat. Do your diagnostic work first. coolant level cold, test drive, and MAKE SURE IT IS RUNNING HOT before you start replacing parts that yoou do not need.

[69GMCLonghorn]

Originally Posted by cdowns

sounds like the fan you're using is not adequate// maybe try a larger capacity fan or a 2fan setup

One more thing: Why run one of those toy fans to begin with? Just run a regular fan with a fan clutch... These trucks did not overheat from the factory with A/C. With the addition of a fan clutch, the drag is minimal. I mean honestly, if you're trying to put less "drag" on the engine, you are putting perfume on the proverbial PIG! Don't bother!

If you're overheating and running less than a 500 HP blown engine, something ain't right and is probably plugged or about to fail.

[davebloomer]

Thanks guys.. Ill keep it all in mind as I go to working on it.


I had the issue before the fan was installed (part of the reason for getting it). It seems to pull huge volumes of air. I got the idea from this boards FAQ's and many others seemed to have good luck with it. I felt that since I was heating up at lower RPM's it may help to have a fan that does not depend on engine RPM to spin it.

[mclairmo]

If different fans don't help, then airflow is likely not the problem. Coolant flow may be the issue here. Do you have underdrive pulleys? Also, are you running vacuum advance? Is the carb running lean? No vacuum advance and a lean carb can cause heating issues.

[BCOWANWHEELS]

I had bad luck with my jeep electric fan, it ran hot too. Even on my 6cyl. 250 engine and a 160 thermostat. No way would it cool my 350. I went back to my 7 blade fan and clutch setup and it solved my problem.

[WorkinLonghorn]

I'm with cparman on this one (post #5 above). There is NO WAY that the system will shed 35 degrees in 15 seconds period!
Now maybe you were exagerating,but in any vehicle I've ever had,that kind of heat would take 3-4 minutes at fast idle, easy.
So I'm thinking your reading is faulty.
Two different fan systems,same result? Yeah,doesn't sound right,then a 15 second cool-down?
Try a different sender and gauge or use one of those point and shoot thermometers that uses laser (I just got one pretty cheap) and take a reading at the neck and see what you get.
Incidentally,these trucks were designed to run 195 degree thermostats and 15 psi radiator caps (with AC,heavy duty cooling or Big block).

[unclewatts]

Originally Posted by WorkinLonghorn

Incidentally,these trucks were designed to run 195 degree thermostats and 15 psi radiator caps (with AC,heavy duty cooling or Big block).

Workinglonghorn is right. I got a 195 degree thermostat and 15 PSI cap on my 350 and it runs cool as the proverbial cucumber. BTW, Harbor freight sells those laser non-contact thermometers for about 40 bucks. I bought it to check my tube amps.

[davebloomer]

Originally Posted by WorkinLonghorn

I'm with cparman on this one (post #5 above). There is NO WAY that the system will shed 35 degrees in 15 seconds period!
Now maybe you were exagerating,but in any vehicle I've ever had,that kind of heat would take 3-4 minutes at fast idle, easy.
So I'm thinking your reading is faulty.
Two different fan systems,same result? Yeah,doesn't sound right,then a 15 second cool-down?
Try a different sender and gauge or use one of those point and shoot thermometers that uses laser (I just got one pretty cheap) and take a reading at the neck and see what you get.
Incidentally,these trucks were designed to run 195 degree thermostats and 15 psi radiator caps (with AC,heavy duty cooling or Big block).

Yeah I believe I will start with my guages.

[69GMCLonghorn]

Maybe they did come with a 195 stock, but I'd never run one now. There isn't any reason to run an old engine at 195. They'll run just great at 160.

[davebloomer]

New development..... It heats up when in gear (low rpm) at a stop. If I simply put it in park (faster idle) it seems to cool down rather quickly.

[mclairmo]

Low coolant flow is the issue, raising the rpms increases coolant flow. You must be running underdrive pulleys or have a bad water pump or there is a resitriction in the system preventing adequate coolant flow, like maybe a bad T-Stat or plugged radiator or engine coolant passages.

[mr48chev]

Originally Posted by mclairmo

Low coolant flow is the issue, raising the rpms increases coolant flow. You must be running underdrive pulleys or have a bad water pump or there is a resitriction in the system preventing adequate coolant flow, like maybe a bad T-Stat or plugged radiator or engine coolant passages.

That was my thinking, either the block or radiator are plugged somewhat, or there is an issue with coolant flow.

Does it have the correct waterpump? Meaning is the pump designed for the belt system you have and run in the correct direction? This can be a problem when guys swap in a later engine and then run V belts on it.

Is the outside of the radiator clean and free of bugs and other trash, dirt and grease. I have a Van out here that fried the engine because they had a trans cooler leak and the oil and dirt had half the radiator plugged.

[WorkinLonghorn]

Maybe they did come with a 195 stock, but I'd never run one now. There isn't any reason to run an old engine at 195. They'll run just great at 160.

Sorry for the hijack davebloomer, but I wanted to respond to the esteemed 69GMCLonghorn by saying that on my truck at least,with a 195 degree thermostat, If I get on the freeway on-ramp and the temperature gauge is ANY less than the full 195 warm-up, The loss of power is very noticable. I's not "a little" loss, It's "Oh crap,where's my power?" loss.
Maybe it has something to do with fuel atomization in an engine that is running at the temperature designed by the engineers.
Don't know,but I would never dream of putting a 160 in mine and running around with less than max power,not to mention milage.
And what would be gained exactly?

[texanidiot25]

Running the motor too cool does effect fuel burning and efficiency. In fact, you'll notice a lot of late 70s and 80s cars run normal temps over 200 degrees, it was a cheap trick to clean up emissions that did not effect performance. Not over heating, my 3.1L V6 Firebird ran 220-230 if I remember right.

[mclairmo]

Yikes, if any of my old cars/trucks went up to 220-230 I would sh!t my pants. I would rather have them run at 160 and lose some (even a lot of) power and fuel efficiency just so I would not have to worry about the engine exploding on me. I hate having to watch the temp gauge more than road and I've been there before, no fun at all.

[mvfd70]

i've had vehicles that ran normal at around 220-230 degrees. Fuel atomizes better there and burns better. yeah water boils at 212 degrees but Thats at atmospheric pressure. If you're running a 15 psi radiator cap, then your cooling system is at somewhere just below 15 psi. A liquid under pressure has a higher boiling point. I'm not a physics expert but 220 degrees is not overheating an engine.

[davebloomer]

alright thanks guys.... It is a 94 model block so i will look into the water pump. Probably need to find a radiator shop too.

[texanidiot25]

Originally Posted by mvfd70

i've had vehicles that ran normal at around 220-230 degrees. Fuel atomizes better there and burns better. yeah water boils at 212 degrees but Thats at atmospheric pressure. If you're running a 15 psi radiator cap, then your cooling system is at somewhere just below 15 psi. A liquid under pressure has a higher boiling point. I'm not a physics expert but 220 degrees is not overheating an engine.

For every 1 PSI of pressure you put on water, the boiling point is raised by 1 degree F.



Public education did do me some good!

[davebloomer]

Originally Posted by mclairmo

Low coolant flow is the issue, raising the rpms increases coolant flow. You must be running underdrive pulleys or have a bad water pump or there is a resitriction in the system preventing adequate coolant flow, like maybe a bad T-Stat or plugged radiator or engine coolant passages.

Can anyone fill me in on what waterpump/pulley setup I should have... seems to me like this is the issue.. seems like a smaller pulley would increase rpms to the pump causing it to circulate better right?

I have a 94 350 in it... I will take pictures tomorrow where we can see what I'm even talking about... should've waited to post.