1987 Chevrolet 350 tbi high idle

[Bextreme04]

Tomorrow I plan on driving the truck down the road and seeing how the temperature acts. It was getting warm today but never got to 260 as far as I saw while trying to get air out of the system.

The pulsating pressure in the upper hose and all of the other things you have said make me think the water pump is probably not in good shape. You are probably getting not nearly enough coolant flow through the engine and its getting localized hotspots. I would change the water pump ASAP before doing any more driving. I would also look at getting a better fan.. that three blade is pretty weak. The mechanical idle with the A-B pins shorted should be 650rpm. The IAC valve should then be pulling idle up to ~750rpm. Change the IAC and then do the IAC calibration and idle set procedures. Get a timing light and actually adjust it properly.

 

[AuroraGirl]

The truck after a few starts did settle down and quit the popping that was occurring. The idle seems too slow in my opinion, the truck doesn’t sound like it’s running at full potential, I feel like 750 would run better. The truck kinda shakes at 650 and if you accelerate and let off it bogs and runs rough then smooths back out to 650. The new IAC came in today will install in the morning just as an extra insurance.

install it only after you fix your timing stuff and other things.. you need to set the idle is why its sounding strange now.

 

[AuroraGirl]

The pulsating pressure in the upper hose and all of the other things you have said make me think the water pump is probably not in good shape. You are probably getting not nearly enough coolant flow through the engine and its getting localized hotspots. I would change the water pump ASAP before doing any more driving. I would also look at getting a better fan.. that three blade is pretty weak. The mechanical idle with the A-B pins shorted should be 650rpm. The IAC valve should then be pulling idle up to ~750rpm. Change the IAC and then do the IAC calibration and idle set procedures. Get a timing light and actually adjust it properly.

Also his shroud should be repaired or replaced. this combined would probably all get his fan where it "should" be which i believe the reason it appeared inset before was the broken part. He should get a neew clutch too

 

[iamtherealJayy]

@AuroraGirl how can I get a new fan/clutch assembly? I looked up fans and most of them are just electric fans? Is there something more specific I can call it to order a fan? And I’ll work on getting a water pump too.

 

[AuroraGirl]

@AuroraGirl how can I get a new fan/clutch assembly? I looked up fans and most of them are just electric fans? Is there something more specific I can call it to order a fan? And I’ll work on getting a water pump too.

you need a mechanical fan for a sbc just find one thats good diameter and more than 3 blades and probably not a plastic one. the clutch is just a fan clutch for your year

as far as SBC goes it should just "work" when not counting serpentine setups(not yours)

 

[iamtherealJayy]

When looking for a fan should it just be the fan or should there be a pulley or anything with it? And the fan clutch is just a replacement just to replace it because I’m changing the fan?

 

[iamtherealJayy]

@AuroraGirl do you know the general diameter fan I need? I’ve seen 16, 17, and 18-1/4 so far. I’ve seen a lot of 6 blade fans. None of them say specifically for a small block Chevy. I’ve never had to get a fan but looking up a fan at oreillys everything that comes up is electric, with the exception of a $220 fan clutch, and a few blade that don’t say anything about my vehicle.

 

[AuroraGirl]

Try google. youd have better luck than just oreillies

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[iamtherealJayy]

Do you know about what diameter I need? I have seen several sizes from 15” to 19” fan blades. Also is it just the pictures or are the 5 blade fans disproportionate? It looks like three fins on one side then 2 on other side? I’m seeing a lot of plastic fan blades, a few steel, and a lot of different sizes. I may go ahead and work on getting a water pump and while I’ve got the fan off measure everything about it like the size and center hole it looks like matters maybe? You asked last night about how the fan spun? What should it feel like? I don’t figure it should spin freely? If I tried to spin mine it spun until I stopped pushing it.

 

[AuroraGirl]

Do you know about what diameter I need? I have seen several sizes from 15” to 19” fan blades. Also is it just the pictures or are the 5 blade fans disproportionate? It looks like three fins on one side then 2 on other side? I’m seeing a lot of plastic fan blades, a few steel, and a lot of different sizes. I may go ahead and work on getting a water pump and while I’ve got the fan off measure everything about it like the size and center hole it looks like matters maybe? You asked last night about how the fan spun? What should it feel like? I don’t figure it should spin freely? If I tried to spin mine it spun until I stopped pushing it.

take a tape measure
go fix your shroud with some epoxy
measure your opening and also center on the spot that sticks out off the water pump pulley. so if you have to span 19 across centered on the pulley and it fits in the shroud dimensionally, go to town. you want to size it to be smaller than the opening of course, but not too small. i cant tell you how big your stuff is lol

 

[iamtherealJayy]

I didn’t know if there was like say 17 is standard and 19 would fit and 16 was for light use or something so I asked oops. If I get off work in time today I’m going to get the timing set at 0° and replace the iac after. And then see what the temps are doing. Possibly buy a new water pump.

 

[75gmck25]

The fan and shroud diameter must be matched. A rule of thumb is that the fan is about 2” smaller diameter than the shroud opening, so you have at about 1” clearance all the way around.

Heavy duty GM cooling systems will use a fan with more blades and/or a sharper blade pitch. I think my HD fan has 7 blades. However, the HD fan would load the engine down too much if running all the time, so they also use a fan clutch. There are light, medium and HD thermal clutches, and they change the rpm where the clutch engages and where it starts to free-wheel. For example, the Hayden HD clutch runs the fan at 20-30% of engine speed when cool, and 80-90% of engine speed when exposed to hot air.

Its also good to use a heavy duty 195 degree thermostat that has a bleed hole, or modify your stock thermostat by drilling a 1/8” hole in the outer section. That hole allows a small amount of coolant through even if the thermostat is closed, so it helps bleed air out of the system.

I’ll also repeat Auroragirl’s suggestion - start a new thread with each of your specific problems. Following a 24 page post with multiple problems is too complicated.

 

[iamtherealJayy]

@75gmck25 the truck definitely doesn’t get used for heavy duty work. I only use it for light driving to places, only pulled a trailer once and my master cylinder went out lol. Not a race truck so I never get above 3000 rpm, fastest it goes is about 60. I saw the Hayden fan clutches and I’m looking at some 6 blade fans on amazon, the reviews are saying they cool small block chevys amazingly. While I’m changing the water pump I’ll measure the shroud and fan etc. Im not positive how to tell if a fan clutch is going out but the fan spins with the engine on and with engine off the fan spins as far as you push it, it doesn’t freely spin.

 

[AuroraGirl]

@75gmck25 the truck definitely doesn’t get used for heavy duty work. I only use it for light driving to places, only pulled a trailer once and my master cylinder went out lol. Not a race truck so I never get above 3000 rpm, fastest it goes is about 60. I saw the Hayden fan clutches and I’m looking at some 6 blade fans on amazon, the reviews are saying they cool small block chevys amazingly. While I’m changing the water pump I’ll measure the shroud and fan etc. Im not positive how to tell if a fan clutch is going out but the fan spins with the engine on and with engine off the fan spins as far as you push it, it doesn’t freely spin.

5 blade.3 5 7 9 blade is the number of blades you wanna follow.

Why?

Balance, noise, etc.

 

[iamtherealJayy]

So I should focus more on odd numbers and not just settle for a 6? The only bad things I saw in the reviews for the 6 blade was wind noise one person compared it to a supercharger. One said jet engine. So I mean if I moves air no biggy, my truck is by no means quiet but it’s not obnoxiously loud. A little fan noise won’t bother me