Engine rev's High when start, overheating

[Designer5]

I just took a long trip in my 95 blazer, about 1300miles. I changed the belt before hitting the road. I noticed before I left that my engine started to rev high when I start her up, but after a minute it calms down. Now that i am out of state I am noticing that my engine is real hot and the temp has red lined once. I is running an average of 230. heres the thing when I have been driving and the engine is hot, then turn it off go into the store come back out and start it, the engine rev's high and then the temp red lines just about and hardly moves back down to a cooler temp.

I am thinking about relacing the Thermostat to see if this does anything. I had the water pump replaced about 3 to 4 years ago.

Any help would be appreciated!!!!!!!!!!!!!!!

Tony

[Chris Stewart]

The thermostat change is a good idea.
What's the RPM indicated on the tachometer on your instrument panel when it's reved up?

[Designer5]

2 Door, no tachometer, I would assume very high maybe 5000 to 6000 rpm's,

Here a few ?

What would cause the engine to rev so high on start up?

Is an average engine temp at 230 ok?

What else could cause the engine to run so hot (I see no leaks), Also I am in florida?

[ericn1300]

Originally Posted by Designer5

2 Door, no tachometer, I would assume very high maybe 5000 to 6000 rpm's,

Here a few ?

What would cause the engine to rev so high on start up?

Is an average engine temp at 230 ok?

What else could cause the engine to run so hot (I see no leaks), Also I am in florida?

lots of things could cause the hi revs on start and an engine temp of 230 is not going to kill a 4.3, i don't think the fan even kicks in until 235, but you should get it fixed soon before it goes higher. should be running between 195 and 210. so what have you've done so far?

when was the last coolant flush and pressure test?

and when was the last major tune-up (plugs, plug wires, dist cap, etc.) done?

[muddog321]

235 is a bad - 195 is operating and if its going over 210 I'd worry and say the system is clogged, the cap is not holding pressure, thermostat not opening, or the fan clutch is shot. You will blow a head gasket soon. I'm in FL and at 100 outside at idle in traffic with AC never over 210!

As for the revving do you smell gas and hows that CPI and nut kit (gas lines) under the upper intake - may be leaking internally. Or could be a sensor but until you get the overheating fixed (could be triggering the rpm surge) you will not have a stable air/fuel mix to fix.

[Chris Stewart]

Do you have a Check Engine light on?
A stuck open Idle Air Control valve (IAC) will let one rev up pretty high. Combine with the fan clutch pulled in and it'll sound like a runaway jet.
You can try wiping the plug valve of the IAC with a rag wet with carburetor cleaner (don't spray the IAC and don't push or force the IAC plug valve) ,
spray some carburetor cleaner and wipe inside the intake manifold hole where the IAC resides, reassemble and see if the RPM upon start returns to normal.
Check for disconnected vacuum lines...are the brakes good?

[1996LTOwner]

After flushing my '96 it would red line and the heater wouldn't work. It was low on fluid. Had to refill about three times before the system was full and all the air had circulated out. If all you did was replace the belt, I'd double check the routing to make sure you have it exactly as it is shown on the sticker under the hood.

[Designer5]

Well I am going to start with the theremostat then see what happens. The temp gauge seems to bounce around.

Where is the drain plug located, Is it on the bottom of the radiator?

95 blazer, 2 door, 4x4, 4.3 vortec

[1996LTOwner]

On the '96 it is a plastic thumb twist that backs out located on the lower back passenger side of the radiator. After replacing the thermostat, you may have to top off the fluid a few times until all of the air is out. If you're going to flush the radiator, pull off the lower hose to get a better flow, The "petcock" drains pretty slow. The temp indicator will go up and down if air is in the system. When the temp sensor isn't submersed it will read a higher air temp and then cycles back to actual water temp when it gets covered in water again.
Good Luck.

[Designer5]

Ok I decided not to replace it my self and took it to get it fixed, they couldn't get it to overheat. I guess this is cause it really only went red line once, really it runs hot all the time at 220-225. Then after I get off the express way in slow traffic it raises to 335. but anyways I had them replace the thermostat with one i purchased for $10 at advanced auto, 195deg. and flush the system and it still overheats.


I had the water pump replaced 3 years ago.

New radiator now?

WHAT Should I Do Now

[blazes9395]

I agree with muddog, its running hot. You have to get that temp down, or you'll have more problems soon.

Pressure test your cooling system. You have to make sure its holding pressure. If it isn't you have a leak somewhere, if it is holding pressure, flush your cooling system, make sure the rad is flowing good, make sure its clean(both inside the rad and outside). Also, if your rad cap is old, or even original, just change it, if its not holding to proper pressure, it will run hot.

As for the high rev, does it rev and calm down and its good for the rest of the time? Id say the best thing to do would be to check for vacuum leaks, and it might be a good idea to get it scanned.

Also, hows the charging system, is it charging properly, hows the charge on your battery?

[Designer5]

It was pressure tested and is holding pressure

System flushed today and replaced thermostat

water pump replaced 3 yrs ago

I will replace the radiator cap, not sure about the condition of the radiator? how would you check if its flowing inside, its prolly clogged up.

as for the battery I have a cheap walmart duralast, But the volt gauge seems to vibrate back and forth a little, the alternator was replaced like 4 years ago.

anymore feedback would be great!!!!!!!!!

Thanks everyone


Oh yeah something else I noticed is that my vent is stuck on blowing air by the windshield and at the floor, which is the same as when you run your heat, even if I use A/C bi level, or vent, it still will not switch to the vents that are blow on the person. Does this spring some ideas

[blazes9395]

There really is no way of testing rad flow, but take the cap off, how does it look inside? The first thing I would do is replace the rad cap and see what that does. I have seen this many times the cap can't hold proper cooling system pressure and you have poor cooling system performance. If that doesn't solve it, pull the rad, plug the tranny line holes, and clean it up real good. Pour some cooling system flush in the ran with it sitting on a floor facing up, and fill the rest up with water, let it sit for a couple of hours, and take the hose to it. Back flush it real good. If its clogged, take your time and you'll get it.

As for the vent issue, the selector knob inside the truck commnly goes bad and needs to be replaced. The default is the defroster. But before changing the knob, make sure your vaccuum lines are good, check the vaccuum source that is on the back passenger side of the upper intake manifold. A good way to test for vaccuum is getting a vaccuum tester and hooking it up inside. This way you'll know right away.

[Chris Stewart]

Your glovebox gurgle is a leaky radiator cap and it needs to be replaced.
On the cheap, you can try washing the radiator/air conditioner condenser with a garden hose with good pressure and check for trash, grocery sacks, birds nests and so on, that could be blocking airflow.
I put a piece of cardboard in front of the radiator in the cold winter to help the motor warm up on my truck and take it out when the weather warms up.

[Designer5]

Bare with me please...............

Ok I think i am getting somewhere but have wasted time and money!!! oh well at least I am learning something.

Anyways I replaced the radiator and still the same engine running HOT.

I took the blazer to AAP, and got the engine light diagnosed, the code came back P0507 "idle control system" RPM HIGH. I can hear a hissing sound if i put my head near the engine also.

I think I have been going in the wrong direction with the new thermostat and radiator. I checked my oil after a 30min drive and found about 6 to 8 tiny bubbles on the end of the dip stick. How would I check if I have blown the intake gasket or head gasket?

SOMEONE HELP