SBC 350 gets hot above 50MPH. Why?

[nicholastheczar]

I have a 1970 with a SBC 350 and 700r4. I'm cooling it with a griffen 19x26 aluminum radiator and a flexalite mech fan with med duty fan clutch. I have full homemade shroud and a new reverse flow water pump. It runs at about 190* when cruising around town under 50Mph. At low speeds or crawling it runs fine. I went to Cruise Moab and had no overheating issues. When I drive it on the highway over 50mph the temp climbs to 210+. My RPMs are never above 2k, usually around 1700. If I slow back down to under 50 it starts to cool down to 190ish. Any ideas?

 

[elbigsam]

Weird turbulance from homemead shroud? Have you tried it shroudless

 

[TOBASH]

In any car there may be several reasons:

Dirty water ports in engine. Need an engine wash-out.

Bad water pump/defective pump even if new. Why go reverse flow instead of normal everyday GM designed flow?

Maybe rad hoses need re-routing as you have them backwards (ie.: with your reverse system remember inflow goes to top and outflow comes out bottom.)

Fan clutch is defective even if new.

You did not bleed all air from highest point in system.

Paper or crap blocking water flow in radiator.

A hose kink needs an inner hose spring to keep hose patent.

Too much ethylene vs water ratio.

Too many RPM at highways speed due to gearing issues.

Those are possibilities I would start with.

Best,

T

 

[yzftaco]

Mine does the same thing.... Crawling or cruising around town I'm at 180* all day..

If I hit the freeway and get above 60 it rises to 200-205* until I slow down..

I'm sbc350 with stock radiator, and a sm420

 

[fieldsken1]

In any car there may be several reasons:

Dirty water ports in engine. Need an engine wash-out.

Bad water pump/defective pump even if new. Why go reverse flow instead of normal everyday GM designed flow?

Maybe rad hoses need re-routing as you have them backwards (ie.: with your reverse system remember inflow goes to top and outflow comes out bottom.)

Fan clutch is defective even if new.

You did not bleed all air from highest point in system.

Paper or **** blocking water flow in radiator.


A hose kink needs an inner hose spring to keep hose patent.

Too much ethylene vs water ratio.

Too many RPM at highways speed due to gearing issues.

Those are possibilities I would start with.

Best,

T

i agree with all above except for routing the radiator hoses. that will have nothing to do with it. all that would do is make the h2o pump work a little harder pushing the water uphill. the motor does not care which way the water flows from. but if you do have a reverse pump on the blades inside the pump wont work right i/e the blades will be backwards. on a 70 motor i dont knoqw why you would have a reverse pump anyway. another reason could be it that you stated that you are using a med duty fan clutch and they spin at about 60/75 percent of the motor rotation so a heavy duty fan clutch might be an answer also since they spin upwards of 90 percent of the rotation of the motor. the pitch on the fan blades may not be enough either

 

[jimd4x4]

Reverse rotation fan and fan clutch. I am guessing you are using the serpentine belt setup? Which is why you have a reverse rotation.

 

[reddingcruiser]

A picture of your shroud might help. Assuming all is well with the water pump, hoses, water jacket, timing, etc., there are a number of things that can be wrong with the shroud - including:
1) The placement of the fan relative to the back of the shroud.
2) Fan pitch at speed (flex fans, especially).
3) The gap/clearance between the fan blade tips and the shroud.
4) Any gaps between the shroud and the radiator on the backside.
5) Any gaps or the distance between the radiator and bib.
7) Placement of the trans cooler, if equipped.
8) Winch type and location, through the bumper or above the bumper, cover or no cover - anything that disrupts air flow at high speed.
6) Fan clutch efficiency.

There is a reason why propeller-driven planes have a maximum theoretical air speed, particulary in a dive. At some point there is only so much air that can be moved by the engine and propeller, after that the air in front is effectively compressed. Essentially, anything that helps move an unobstructed/lateral air flow maximizes cooling and anything that defelcts air flow or creates cavitation is bad.

 

[nicholastheczar]

Thanks for the replies. I do have a serpentine setup which is why I have the reverse rotation water pump and fan. I have a trans cooler and power steering cooler in front of the radiator.

Give me a quick run down on the proper technique for bleeding the cooling system.

I'll try to get some pics of the shroud. I have about half and half of the fan inside / outside the fan shroud.

I was also wondering if my fan clutch wasn't working properly. I've thought about switching to a HD version to see if this fixes my issues.

I'm TBI if that matters.

I have a warn 8274 on the front of the cruiser, but it did the same thing before I put that on there.

 

[Bret]

I have read that cooling at speed is generally a function of radiator surface area. It sounds like you have that covered though. Could your TBI be leaning out at cruising speed? Would it be worth it to bypass the coolers and remove them for a quick run down the road? Does the radiator have any dirt in the fins? I actually pulled mine out and hosed it off in the driveway, there was quite a bit of dirt and mud stuck in the fins.

I'm running a 19x26 Al radiator with a 7 blade clutch and never had a cooling issue with my SBC.

 

[fieldsken1]

I have read that cooling at speed is generally a function of radiator surface area. It sounds like you have that covered though. Could your TBI be leaning out at cruising speed? Would it be worth it to bypass the coolers and remove them for a quick run down the road? Does the radiator have any dirt in the fins? I actually pulled mine out and hosed it off in the driveway, there was quite a bit of dirt and mud stuck in the fins.

I'm running a 19x26 Al radiator with a 7 blade clutch and never had a cooling issue with my SBC.

what 7 blade clutch and fan are you using????????????

 

[LittleMan]

" I have a trans cooler and power steering cooler in front of the radiator.


I have a warn 8274 on the front of the cruiser, but it did the same thing before I put that on there.[/QUOTE]


These 3 things are likely Greatly reducing the effective surface area of your radiator. I had similar issues recently and relocated the trans cooler to one side of the radiator versus the center, opening up a larger area of radiator surface. (fan pulls harder @ center than @ edge of shroud) It got me about 15 deg cooler @ highway speed. HTH.

Jason

 

[Cdaniel]

This could be as simple as the lower hose collapsing at high RPM's/speed. I think TOBASH's inner hose spring is a good simple cheap start point.

Even if you know there is a support spring / wire in there, check to see if it's corroded away.

 

[camcruiser13]

Maybe the water is not staying in the radiator long enough. Small radiator fast flow not able to cool it before it heads back In to the block

 

[fieldsken1]

Maybe the water is not staying in the radiator long enough. Small radiator fast flow not able to cool it before it heads back In to the block

i stated that once and everyone said it does not work that way so i guess i was wrong. but thats ok i know i was right

 

[bikersmurf]

At 50 mph, the fan is of little benefit. I'd say the fan clutch was the problem if it was overheating at idle... But not at that speed.

The tranny cooler could actually be preheating the air coming into the rad.


Could engine timing, or lean fuel mixture also be contributing?

 

[FishNinJay]

Maybe the water is not staying in the radiator long enough. Small radiator fast flow not able to cool it before it heads back In to the block

Isn't this the rationale for trying a higher temp thermostat? to try and keep coolant in the radiator longer.. before recirc?

 

[bikersmurf]

It's sure a puzzle. With my stock 1970 Chev water pump with a smaller pulley (to make it spin faster) I've driven 25 of 27 hours straight at 65 mph (close to 3,000 rpm with stock 4 speed) without overheating problems. I'm running a recored stock 3 core rad (with higher density core). And no, it wasn't up north here... Trip was Pheonix, Arizona to Vancouver, British Columbia... (Although in the fall).

I'd guess one or more of the following is causing the problem...
1) fuel mixture and/or timing making engine run hot.
2) tranny cooler in front of rad.
3) something restricting coolant flow.

 

[nicholastheczar]

As far as the mixture, I'm not getting any check engine lights on when I drive it.

Both my tranny and power steering coolers are in the middle of my radiator, I may try moving them and see what happens.

My lower hose is a 1.5 year old Gates green stripe hose, I'll check it, but that thing is pretty beefy.

The one thing I have never looked at on this engine is the thermostat. If I remember correctly an 88 SBC TBI motor likes a 192* thermostat. Does this sound right?

My timing has always been an issue on this motor. When I got it, there were no timing marks on it and I have had a hell of a time getting it timed correctly. I took it to a mechanic to have him time it, and it came back running worse than when I took it in.

Lots of good info here. Thanks guys!

 

[pb4ugo]

I heard TBI sbc's need a 190* plus tstat. Does it stay around 210* or does it continually climb?

 

[Brian in Oregon]

Don't overlook the possibility of spinning the water pump too fast.

Water has to remain in the radiator long enough to transfer heat though the tubes and fins to the air. If there is not enough dwell time, the water will not have an optimum amount of heat exchange. This can be a problem with high flow water pumps, especially when used with smaller pulleys. If your setup is like this, you might try going up a couple of inches in diameter for the fan pulley.

In fact, for some air conditioning applications, particularly MOPAR, a smaller impeller was used to slow the water flow through the radiator, because the air conditioning condenser preheated the air, reducing cooling. I'm not familiar enough with individual SBC applications to know if GM used a smaller impeller like MOPAR, but, a larger diameter pulley would accomplish the same thing.

A rare out of left field problem could be a mismarked pump. You said it's supposed to be a reverse rotation. But, there have been cases of the wrong impeller being used, or some parts jockey puts two pumps on the counter for a customer to look at, then accidentally mixes the boxes up.