350 is overheating in idle/park/heavy traffic

[Bull72]

Can someone provide some insight to this issue I am having? My 1972 blazer is overheating when in drive but not giving it any gas. For example I was in very heavy traffic today and it was stop/go and it started overheating quickly. It will also overheat in idle or at the drive through.

As soon as I start driving though the temperature goes down. Has anybody had this issue before? What would be the suggestions to look at. I take my truck to the same shop and they told me they weren't sure what the issue was. So far I have replaced the radiator, put in a failsafe thermo. and the temp guage is working good. When driving it shows cool and heats up a little when driving long distances. As soon as i am in traffic or park/idle though it just rises.

Any suggestions?

[turp mcspray]

Are you running a shroud, clutch fan, and the stock pulleys?

[Critter]

Fan clutch came to mind. Can you give any more info on the engine itself? Recent rebuild, original 72 engine, is it built up for extra horsepower etc?

[mdunn]

After you check the above mentioned, check your timing also.

[AlaskaMatt]

Fan clutch. Mine acted exactly how you describe when it went out.

[Bull72]

Originally Posted by Critter

Fan clutch came to mind. Can you give any more info on the engine itself? Recent rebuild, original 72 engine, is it built up for extra horsepower etc?

Thanks everyone!

It has a fan shroud. Not sure about the pulleys though. Im not sure if you can tell from these pics but I attached a couple. As for the engine it was rebuilt about 9 years ago and then sat for 6 and has been running the past 3 years. I believe it has a performance cam. I will take it back to the shop this week and ask them to check the fan clutch and timing for me. Thanks again everyone and I will give you the verdict after it gets out.

[Critter]

Well, let us know.

[Bull72]

The beast is in the shop today, I will let you know what they say...

[Bull72]

I have not picked it up yet, but they told me they found the issue my rad fluid was low. But I'm not so sure that was it because I just changed the radiator out last month and filled it myself.

They told me after filling the rad up they tried to "recreate" the overheating and it wasn't overheating. So shame on me if that's all it was.... but have a feeling today's weather could affect their testing because it is pretty cold here in San Antonio today. We shall see when I pick it up tomorrow and take it for a cruise.

They did recommended that I get an overflow tank for the radiator fluid because even if it is full it may burp some fluid out of the hose and without the overflow tank... obviously can't suck any more up. That makes sense to me and would explain why the coolant may be low.

updates to come....

[tubbedII]

Well, from what I've read (mostly from a lot of cdowns' posts), the radiator is supposed to be about 1'-2" low on these things since there is no overflow/resevoir tank. For the first few drives in mine, I kept filling it up but noticed it always went back down to about that level. Now I just keep it there, and check it about every 4-5 drives...doesn't seem to move.

[cleszkie]

You can develop steam or air pockets if the system if not properly bled or burped. If your shop didn't have the wherewithall to check things like fan clutch, timing, and coolant level before they tell you they don't know what the issue is, its time to get a new shop in my opinion.

If you continue to have the problem, check timing. Too much advance will run hot. Also check fuel mixture at idle. A lean mix will run hot. Good luck.

[Bull72]

So I guess it was shame on me for not trying more rad fluid first I didn't check because when I changed out the radiator I filled it to the top. Brand new rad so it was not leaking at all. Their thoughts were as it was burping out the extra fluid maybe the suction let too much go. I drove the truck home yesterday in traffic and it stayed cool and didn't rise above the cross hatching of the most left cool area of the gauge, so I was happy.

Until this morning....I'm waiting on the tow truck now. dohh: I tried to start it this morning and it won't start, it is cranking very slow and isn't turning over. Will let you know what it is this time. My poor truck on the flatbed...

[AJs72K5]

I'm going to assume that when you removed the lower radiator hose, you dumped a bunch of fluid from the block. Just filling the rad when you put the new one on wouldn't have accounted for that.

Typically you'd want to install the new rad without the thermostat to help bleed it. Run the engine for a few mins to circulate coolant, reinstall thermostat and top the coolant off.

[Bull72]

Originally Posted by AJs72K5

I'm going to assume that when you removed the lower radiator hose, you dumped a bunch of fluid from the block. Just filling the rad when you put the new one on wouldn't have accounted for that.

Typically you'd want to install the new rad without the thermostat to help bleed it. Run the engine for a few mins to circulate coolant, reinstall thermostat and top the coolant off.

You are probably right AJs72k5 when I put on the rad and filled it up I did let it run for a few minutes to let it cycle. But I did nothing with the thermostat... I heard once that some guys have skills and some have bills, I am most definitely the latter!

[mdunn]

You can also leave the radiator cap off the first time and watch the level fall as the thermostat opens. After it does, continue to fill slowly to the proper height, and put the cap back on. After it cools, check the level again. Top it off if needed. Little less work than pulling the thermostat, but either way should work.

Did you check the battery voltage before you had it towed? sounds like you just needed a new battery.

[Bull72]

Originally Posted by mdunn

You can also leave the radiator cap off the first time and watch the level fall as the thermostat opens. After it does, continue to fill slowly to the proper height, and put the cap back on. After it cools, check the level again. Top it off if needed. Little less work than pulling the thermostat, but either way should work.

Did you check the battery voltage before you had it towed? sounds like you just needed a new battery.

Did try jumping the battery but it was brand new (replaced the battery about 3 weeks ago) because it was swelling, no luck. A few weeks ago the alternator was putting out higher voltage than was called for and so they put on an external regulator. They guessed the alternator was running like that for so long (before I owned it) that it caused it fail. They are replacing it now and should be ready to go this afternoon.

[Bull72]

Thanks everyone for your help, if it overheats in idle again I will have them check the fan clutch and timing as well. I'm also planning on adding that overflow tank within the next few weeks just as a little extra precaution and looks of the chrome fluid container.

As for the immediate moment we are back in business. Today it needed a new alternator and my shop whipped that out this morning. Blue Thunder was nice enough to give me a ride and pick up my beast.... good to see a couple of K5's together on the road, can't wait to see a big group of us somewhere here in San Antonio when everyone is ready.

[mr48chev]

Just out of curiosity, what ratio of antifreeze to water are you running in the radiator?

It's pretty common to see guys who moved up here from southern areas beside the road with their rig steaming on the first day that the temperature drops below freezing but if your rig tends to cool off when you get up to road speed that wouldn't be the problem/

Also how high is High on the temp. All the way to the top or just up above normal more than usual.

You have the short pump so pump rotation shouldn't be an issue in this case.

I'm inclined to think that the fan clutch isn't working right, that's fairly easy to check if the fan keeps spinning for a while after you shut the engine off or if there is any oil leaking out of the hub or if the fan feel loose when you move it fore and aft with your hand, it shouldn't wobble at all.

Also early or late timing will cause issues with the temperature.

[BLUE THUNDER]

No sweat Bull. I had a good time today. You've got a nice rig. You're def right about getting a couple of other rigs together and hanging out. We'll see about putting something together once the weather gets better.

[yellowdawg]

ill buy your hard topper

[Bull72]

Originally Posted by mr48chev

Just out of curiosity, what ratio of antifreeze to water are you running in the radiator?

It's pretty common to see guys who moved up here from southern areas beside the road with their rig steaming on the first day that the temperature drops below freezing but if your rig tends to cool off when you get up to road speed that wouldn't be the problem/

Also how high is High on the temp. All the way to the top or just up above normal more than usual.

You have the short pump so pump rotation shouldn't be an issue in this case.

I'm inclined to think that the fan clutch isn't working right, that's fairly easy to check if the fan keeps spinning for a while after you shut the engine off or if there is any oil leaking out of the hub or if the fan feel loose when you move it fore and aft with your hand, it shouldn't wobble at all.

Also early or late timing will cause issues with the temperature.

I think it was the Oreiley's pre dilluted 50/50. The temp was rising when in idle/park for too long. and It was rising all the way to the right in in "heat" are crosshatching of the gauge.

It seems to be doing ok now, I still haven't really had the time to fully test it to make sure, but it seems to be running a lot cooler (all the way to the left now). There was a small oil leak and the gasket was replaced and no longer leaking. I will check the fan and see if it is tight as you mentioned it should be.

So when i shut the engine off the fan should still be moving for a few seconds/minutes?

[JOHNORO]

I had the exact same issue on a rebuilt engine.
Turns out it was a bad thermostat (cheap off shore part)
I replaced it and my problem was Gone ...
Posted via Mobile Device

[DANTIP]

Testing the fan-clutch is very easy to do. Roll up a section of newspaper or a magazine and slowly put the edge of the paper up against the moving fan blades. If the clutch is bad, the paper will significantly slow or stop the fan. If it shaves the edge of the paper off, the clutch is good.