The Stovebolt Site Forums The Shop Area Engine Shop 250 running hot

All,

My 250 is running hot, gets to about 235 sitting idling. Cools down a little from that on highway.

New water pump, gauge/sender, failsafe tstat, original radiator was tested/flushed at shop, original fan, no shroud, belt is tight, timing is set, carb is new/rebuilt. Fan is a little far from the radiator, going to put a spacer in.

Any ideas?

I may take to a radiator shop and have them do a leakdown test. The motor has gotten hot a couple of times briefly, maybe blew a head gasket?

I have no idea on the history of the engine.

i dont know if the 250 has a pet cock on the drivers side near the rear of the block or not. if it does remove it and see what comes out. ive had to rod out and flush the blocks on all my trucks in that location. pretty nasty stuff comes out when you start to get it to come out. i like to catch as much as i can. im suprized at how big the pile of crap can get during the process.

Head gaskets going bad will either use coolant and steam out the tail pipe (smell to), or blow coolant out of the radiator overflow. Pull the radiator cap when the engine is at idle and watch for bubbles (not the monkey!) in the coolant.

Fan should be in the 3/4" range from radiator core.

Sounds like air flow problems, since it cools down when moving. I assume you are using stock pulleys? Plugged radiators generally heat up out on the road and can't get rid of the heat through air flow. A lean carburetor will also heat up a engine pretty fast along with a plugged exhaust system.

Get a infrared heat gun and check the thermostat housing, block, head, and radiator to get a idea of true temp of the coolant. Also get a candy thermometer in the neck as a back up. You should see no more then one or two degrees above T-stat temp.

Mine reads about 20 hotter then it really is using the OEM hole between #1 and #2 cylinders. I moved the probe to the T-stat housing and now the gauge read actual coolant temp, 190 right on the money.

i don't know what yoear your truck is but the 250 i put in my 64 ran hot in the summer and towing for 2 years. not as hot as yours but it could creap over 200 sitting at a light. when i would pull a long hill the temp would climb, when i would go down the other side with the truck pushing the engine it would cool down. the orig 6 rad tested ok but i switched it out for a new v8 one and that took care of it. no more fluctuations at lights or hills.

Bumping this up.

As far as head gasket, no smoke, no antifreeze in the oil, no bubbles. It does overflow though. When it gets to 230 or so and you turn it off, the coolant is boiling in the overflow bottle (and howling).

I have a heat gun and my gauge and sender are ok.

Meyer,

I sure don't know the particulars on your situation but 99% of all heating problems stem from a radiator that has plugged tubes. A radiator shop can flush and boil till hell freezes over and those tubes will still be plugged....it comes with age. The radiator is where the rubber meets the road, if it's not transferring heat the whole equation doesn't work.

HEY...a birthday cake! KOOL...

Stuart

as stu says
and my thoughts are you say you got the rad flushed
gettin' flushed is NOT gettin' rodded. in other words have the radiator cap removed and the shop will run a flat bar down each tube making sure all tubes are fully open, so flow is at it's maximum rate. then re-install it.
a wet/dry comp test should be able to tell you if you have a head gasket problem.

I am going to assume that the temp drops to normal when driving on the highway. If so, then it sounds like air flow. the best fan/shroud/radiator installation has the fan a minimum of 1/2 its hub diameter away from the radiator core, followed by a shroud that comes as close to the blades as possible. Moving the fan close to the radiator only moves air in the donut area where the blades are.

your description of no shroud and fan far away from the radiator means that the air is simply swirling around the blades and not moving thru the radiator. if at idle, a piece of card board can not be held against the radiator face by the air, you simply do not have enough air flow.

My recommendation is to simply add a fan shroud, and do not use a spacer. build the shroud to come out to the fan. If you do not want to do that, then remove the engine fan and go electric. with what you described, the fan is doing nothing more than robbing power and making noise.

If on the highway you are not running at the temp your thermostat is, then in addition to air management issues you have either a plugged core, or bad water flow.

Try taking the stat out and replacing it , there are alot of bad stats out there and it is cheap and easy to do, any time I have problems with a new install on a engine and have heat problems it has turned out to be a bad stat the quality control is just not there anymore .


Pete

I bit the bullet on my 235 and bought a new aluminum radiator and it made the world of difference. i had mine back flushed and rodded and wasted enough money to pay for the new radiator. ron got it here.

Get a new radiator, cools down when driving sounds like a bad radiator. Thermostats are cheap, so get a new one to go along with the radiator.

Update... when I last set the timing, I had the vacuum line attached to the distributor still, causing incorrect timing. Reset it, runs at 175 to 190 now, fixed.

51 Ashton, I amwondering if u can give me more info or a pic on this petcock. My father has a 250 chev (dont know hat year) in his boat that is continuously overheating. We have rulled out everything else except the engine. We are installing a new water pump but thats all we can think of- no water in oil or smell so we think the head gasket is good. We did notice that in the coolant lines was a lot of crud from the water cooled manifold so alot of that could be in the engine.

Howdy,

Here's yet another vote for the rad. On a '75 C-10 I used to own, I went through all the same stuff with the 250. I had the rad done and still no success. The only thing that fixed it was a new one, and it was a stock 2 row for the 6 cyl! It didn't look like much, but it worked like a champ!

best wishes,

Les