I-6 engine temp question

[Knoxville71shortbed]

I finally installed an aftermarket temp gauge in my truck, because I only had the idiot lights, and didn't trust them. I have a stock, good running 250 I-6, and have been driving this truck daily for almost 2 years (100 miles per day). In the summer, when it was over 90 degrees and I had been driving for 45 minutes or so, the temp idiot light would come on briefly at stop lights, and then go out when I got moving again. This is what prompted me to install the gauge. Now that I have a gauge, I'm not too sure what a good operating temperature should be for this engine. It seems to run at around 230 to 240 degrees. Is this too hot, under normal conditions? I have installed a new radiator, and like I said, the engine really runs good. I'm just worried about long-term problems from high engine temp. Am I worrying over nothing? What would you recommend to bring the operating temperature down? I haven't replaced my water pump. It shows no signs of being worn out. Could it be that it's not moving the fluid fast enough? I set the timing by ear, since the polution control garbage has been removed (it's a 71, which originally had an air pump). It starts easy, and runs great. Could the timing setting be causing the engine to run hot? The I-6s did not come with a fan shroud. Should I consider installing one. Or am I just paranoid? What do you guys think?

[LeRoy]

Sounds pretty hot to me. I'd try a new t-stat, to start with. Probably a 195 Degree. With my ol 250. I took the factory fan off and installed an electric. I just went to the local wrecking yard and snaged one off of some Chrysler/Dodge. I put some weather striping between it and the radiator and then fastened it directly to it. I did put a 4 core in the truck so I only had to kick on the fan once in awhile in heavy traffic.

[Knoxville71shortbed]

I've already replaced the thermostat, and the heater works great, so I don't think there's a thermostat problem.

[stelth2002]

Fan Shroud!!! I installed one and my temps went doen consideratbly. This was before I started the resto. I dont think I would be able to run without it now, at least not in town. I also have a balnced 7 or 8 flex fan that pulls a lot better than the stock 4. Just a thought. 230 is to high for that engine unless you are pulling quite a load. Mine would be shut off if it went past 200 while not pullin. It not barly climbs up to the middle range.

[72CustomCamper]

Is your existing fan a clutch type or a flex type?

Although rare, the clutches can go out on clutch type fans. Because they operate cetrifugally, that might explain your momentary overheating when at idle...in other words, the fan is barely turning.

With little or no air flow through the radiator, your coolant temp will stagnate no matter how new the thermostat is.

[PICKMUP]

A V8 radiator is wider, so it cools better. Just move the mounts to the outside locations and it fits. The V8 fan shroud will then bolt up. You may have to do some centering on the I6 fan. You still have a heating problem that needs to be found. That I6 with its new radiator, even the smaller one, should handle all your needs and not heat up.

[dashadow]

I agree with PICKMUP. I have a 250 with an old leaky radiator and haven't had a problem. I would try replacing the water pump as soon as possible. I have had one go bad and never leak a drop or make a sound. Easy to replace and not expensive.

[Fred T]

A lot of things could be wrong. You should only be running 190-200 with the 250. What kind of flow are you getting in the radiator? What kind of shape are your hoses in? They have been known to separate and collapse internally. Any changes made to the pulleys? You can turn the pump too fast, and the coolant won't have time to transfer the heat. Have you back-flushed your block? Do you get coolant to flow out the drain on the side of the block? Have you checked the coolant temp with a thermometer to verify the gauge?

I would also get a vacuum gauge and hook it up. It's a great (and cheap) diagnostic tool. http://www.centuryperformance.com/vacuum.htm

[Knoxville71shortbed]

Thanks for all the responses. Based on your points, I will add the following info: the new radiator is a V-8 radiator, the fan is not a clutch fan, just a 4-blade standard fan, all hoses are new, the only change to any pulleys/belts is the removal of the air pump (which I would not think would affect the rotational speed of the water pump), I'm not sure how to check the "flow" in the radiator, I did attempt to flush the block when I installed the new radiator, and I thought the flow seemed good, I was not aware that there was a "drain" on the side of the block (where is it, can you post a pic, must I use this drain to properly flush the system?), I have not yet replaced the water pump. So far, from all your advice, it looks like I should put on a new water pump, and add a fan shroud, and see what happens. Does that sound about right to everyone? Should I give serious consideration to changing the fan to one with more blades? Any other ideas? Thanks.

[Fred T]

Chevy sixes have a block drain on the driver's side. From memory it should be about aft of the exhaust manifold and in the lower portion of the block. It could be just a square end pipe plug or a drain cock. This is a portion of the block that does get plugged with sediment. If you get coolant to flow out, you're okay there. If not, get a piece of baling wire or a similar substitute and start poking around inside until coolant comes out.

Coolant flow in the radiator. I've seen enough that I just know from experience how fast. Warm up the engine with the cap off the radiator. After the thermostat open, watch the flow. It will help if you have another vehicle to compare with. If it barely moves water, the pump or thermostat needs replaced. Since you haven't swapped the pulleys, it shouldn't be flowing too fast. This is also a good time to stick a thermometer in the radiator to check the temp. I use a meat thermometer, then wash it off and put it back in the kitchen. It will give you something to check your temp gauge by.

Now, you said the temp rises when you slow down. Is the 230 reading on the road or stopped? What does it read at both places? And did you check your timing? I set timing on sixes with a vacuum gauge.

I wouldn't advise replacing anything more until you get more info, you can throw a lot of money down the drain in search of the solution.

[72CustomCamper]

It helps to drain the radiator about 4 inches below the cap prior to this test.

Assuming your cap is on the end and not in the center, you will see indications of flow as coolant spills out of the heat exchanger portion of the radiator. With it filled, the best you can hope for is some mixing and swirling.

If you do not want to drain anything, the other sign of a good thermostat/water pump is the sudden surge in level when the thermostat first opens. The hot coolant occupies more volume so a full radiator with the cap off will start to overflow when the thermostat initially opens.

Another thought...what is the pressure setting on your cap?

A 16lb cap means that the cap will port coolant to an overflow canister when the radiator pressure reaches 16psig due to the expansion I mentioned above.

Pressurized (more dense) coolant carries heat from the engine more efficiently so if the cap is bad, your cooling capicity will be lower.

From experience, a BB operates 15-25 degrees warmer with a 7lb cap than with a 16lb.

Either way, if your heater core is getting the hot coolant, than most likely you do not have a water pump problem since it is supplied directly from the pump bypassing the thermostat.

[Knoxville71shortbed]

Hey guys, I'm going to be working on my truck this weekend, to try and remedy this problem. All your suggestions have been good, and I will be using most of them. But I would like some opinions on something that a guy at Advance showed me. They sell a product (I believe it's called "-40 degrees"), which is some form of liquid, that comes in approximately a quart can, and when added to the coolant in your radiator, is "guaranteed" to reduce engine temperature by 30 to 40 degrees. It sounds like snake-oil to me, but I though I'd ask if anyone has ever used this product. It's not cheap. It costs almost $30 for the can. I have no idea what is in it. But the guy at Advance said it does work. Does anybody else think this could be for real? Anybody know what's actually in this stuff? It claims to void no vehicle warranties, and cause no engine problems. I just can't figure out how this stuff could actually work. Opinions? Thanks.

[72CustomCamper]

My .02:

A properly tuned engine needs NO additives. Not in the fuel, oil, coolant, transmission...anywhere.

GM engineers NEVER use additives when designing these drivetrains.

Look into the cheaper possibilities first (radiator cap, thermostat) then move to the other stuff (water pump, temp sending unit, gauge calibration, fan, etc.)

That -40 stuff will cover up a symptom but will not fix the problem.

Let us know what you find!

[72 Chevy Frank]

if you want to check out another collant additive that has a great breakdown of what is in it . Try going to www.redlineoil.com and check out thier product called watterwetter. I use this in my big block 402 to keep the temp down during cruise nights in the summer.

[Knoxville71shortbed]

Just to update those who offered suggestions, here's how it went. I found the block drain plug, removed it, and had very good flow. Determined that there was no obstruction of engine cooling passages. Checked the flow in the radiator, and it didn't seem too good. I went ahead and changed the water pump, and while I was at it, I switched to a 180 degree thermostat. The water pump has helped significantly. The temp gauge now seems to stay between 200 and 210 degrees. It never went above 210, even after driving for an hour. I'm still not sure what the engine operating temp was designed to be, but since the factory installed thermostat was 195 degrees, I assume that they intended the engine water temp to reach 200 degrees. Of course, this is winter, and I don't know what the temp might do when it get's to be 90 degrees this summer. My thinking right now is to leave it as-is for now, and if the temp goes much higher during the summer, the next step would be to add the fan shroud. Does this seem like a sound plan to everyone? Again, thanks for your help.

[Fred T]

Sounds like a good plan. Temp range is usually plus or minus 10 from the thermostat. I recall dad having a Dodge that wouldn't stay cool, the dealer never could figure it out. Finally sold it, but I wanted to tear down the engine and he wouldn't let me. Second and last dodge he ever bought.