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Old 05-04-2008, 07:30 AM   #1
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Bad engine water pump?

I am battling indications of my Suburban’s 454 cid engine running hot at times. Odd things are happening whether towing or not.

The radiator, hoses, coolant, thermostat (two times/ two different brands), fan clutch, plugs, wires, and cap have all been replaced in the last six months.

Compression pressures range between 155 and 165 psi cold. Timing has been checked. There appear to be no internal or external coolant leaks. Overall engine power is good.

Towing my Airstream is one set of heating issues. But just yesterday, I was on the road at 65 mph without my Overlander. The outside temperature was 65 degrees F, and I was not running the air conditioner. The temperature gauge needle was at mid-gauge (normal) the whole time.

A half-hour later, I pulled into a convenience store and left the motor running while I went inside. Returning three or four minutes later, I found the temperature gauge needle at 5/8ths or better of scale.

After pulling away from the store, I could hear the fan clutch engage, and the temperature quickly came down to normal.

On a similar outing, when running the air conditioner, simply pulling up to a red light was enough to make the needle go up.

Now, the needle has yet to go into the red, but it used to never do this. I tend to trust the gauge because the fan clutch’s engagement coincides with the needle going high.

At this point, the water pump is only cooling system component that has not been replaced. But the pump is only 3 years/11,500 miles old and does not leak.

I have never seen nor heard of a GM big-block water pump that went bad by anything other than leaking or seizing. But right now, indications are, to me, that the water pump is not pumping a sufficient quantity of coolant through the system.

Has anyone every seen a case of this?

Thanks,
Tom
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Old 05-04-2008, 08:13 AM   #2
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My first thought was a plugged radiator, but you say that has been changed. How old is the engine? Any chance there is a blockage inside the block someplace? How about a bad sending unit on the temp sensor? Bad wire? Probably not likely.

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Old 05-04-2008, 08:30 AM   #3
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thermostat?
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Old 05-04-2008, 08:54 AM   #4
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What year is it? I had lots of issues with overheating on my 85 SOB Motorhome. I did everything you have done AND added another fan with a toggle switch. When the exhaust manifold went for the second time, I put headers on and ran cooler from then on. No issues at all!
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Old 05-04-2008, 09:01 AM   #5
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I had a similar problem with my old 2000 GMC van. It turned out to be a bad thermostat (which was only a few months old). A "new" part doesn't always mean a "good" part...
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Old 05-04-2008, 10:16 AM   #6
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Mine has always acted that way when I run it for any length of time over 2600 RPM. The 454 is a heat pig.

I have installed temp senders in the oil pan (screws right in the drain plug) and one in the transmission pan trying to figure it out.

When I get into this thermal run away like you are seeing I find that they oil temp and ATF TEMP is up. If I run 70mph (about 2900rpm) for about 20 miles my oil temp gets up to around 260-280F even with Synthetic oil and the factory AUX oil cooler my truck was equipped with. When I get off the hwy the coolant temp spikes like yours.

The temp sender I used is a Hayden that I found at Pepboys. Bought a second sender for the oil pan and I wired them through a switch so I could use a single gage to monitor both oil and ATF.


Does your truck have the factory oil cooler? The one thing I have never checked is the oil cooler set up. I read that the oil cooler has a thermostatic valve and that the oil cooler is bypassed till around 180F of oil temp. I believe it is just a bimetal spring in the adaptor between the block and oil filter. I suppose it is possible that it stick closed. Never looked or tried to jam it open to see what happened with the temp.


My solution has been to drive a max of 65. Fact is at 55-60mph I can squeak 11.5mpg with the AC on 10.5 with 6500lb of Toyota on trailer behind it. 65-70 it was 10mpg with nothing in tow. The wind drag goes up that much and the RPM get out of the motors sweet spot. The 454 is a low RPM motor and it just isn't happy spinning 3k. It really needs Overdrive to run any faster. That why all these MH's pop them in 80k. They spin them at 3000 rpm to move that weight. Shortens the lifespan.

You need to remember when these trucks were built the national speed limit was 55mph. The Cooling system was designed around that.

I did try "Water Wetter" type of product I found at NAPA. It did help some but of course it did not help the oil temps.

You do know there is a bigger radiator then what is listed for the 454 truck? The Diesels got a radiator that was about 4-6 inches wider. If you look at the top of the core-support the mounting holes are there. The Driverside corsuport vertical brace has holes in it to alow the air through it. Just need to junkyard the top plate and its a bolt in.

Does you truck have the factory electric fan? They don't come on until 220F. The sender is in the passenger-side head. You could put a switch on it to over ride.

Other thing to check...they just went to a summer blend of fuel (to lower smog) in Atlanta metro where I live. Its oxygenated and low sulfur. Both of these things will make of a little leaner (hotter) burn. I notice a change in performance when the blends change. Did AL just start adopting this sort of fuel change as well?

Lean will make the engine run hotter. Does your truck have that thermostatic control on the Rochester? It will have a wire running from a temp sender either on the water neck or next to it to a connection on the side of top of the carb.

ESC spark control with the knock sensor? Bad knock sensor might prevent the timing retarding and that could kick the heat up.

To be honest I'm eyeing a really rusted out low mile 89 burb to harvest the 350 and 700R4. A 2wd 1500 Burb of the same vintage can swing 17mpg with a light foot. Its that or sell it.


PS go the the dealer and get a AC Delco thermostat at the factory rated temp.
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Old 05-04-2008, 10:40 AM   #7
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I would try this first....Jet 180 Degree Stainless Steel Thermostat

Installed one in my 95 Burb 454, at 20k and never had an issue in 163k.

As my Dad used to say, keep it stupid, simple.

The only time I've seen a "new" replacement w/p cause overheating is

because of improper assembly. Pump vanes slipping on the shaft. (once in

30yrs in the business.)

More common was improper pump installation, the drive belt was turning

the pump backwards. Not likely in your case though, as this was an instant

o/h problem.

If your using the "red stuff" antifreeze, you might consider a chemical back

flush and replace with the "green"
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Old 05-04-2008, 10:53 AM   #8
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Be careful going with anything but factory temperature thermostats!

If that has the temp sensor for the carb it will change the fuel mixture if you change the temp of the thermostat. If it says a 195F run a 195F.

All the FI from 87 up run 195f from the factory. 87 up runs an normal operating temp of 190-205 and that is what GM set it to run. With the FI if you drop a low temp thermostat in it it will change the fuel mixture. Not sure if that mixture control Rochester will be that sensitive or run that high of a thermostat but it is something to watch out for.
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Old 05-04-2008, 11:04 AM   #9
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Overheating

Tom,
You didn't mention the model year. However, attached is a GM service bulletin for your reference. Sounds as though you been throwing some money at this problem. I would suggest checking your coolant protection level. The higher your coolant protection is above 50%, the engine cooling efficiency is proportionally reduced. Secondly, use a infra-red thermoter or better yet a multimeter with the temperature attachment and check the temp ar various points, radiator inlet and outlet, engine inlet and water pump outlet. A significant temp differance would indicate a restriction between those two points. You've replaced the radiator. I assume it was replaced in-kind (4 core radiator). Holding the fan clutch blade while someone starts the engine, you should feel resistance. If not, worn fan clutch (not a highly recommended practice for just anyone). Also, visually inspect for foreign debris between the condenser and radiator that could impede air flow. Don't overlook checking the fins on your A/C condensor. Good luck,
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File Type: pdf Document ID_ 287108.pdf (69.3 KB, 91 views)
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Old 05-04-2008, 01:04 PM   #10
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Quote:
Originally Posted by lsinclair
Tom,
You didn't mention the model year. However, attached is a GM service bulletin for your reference. Sounds as though you been throwing some money at this problem. I would suggest checking your coolant protection level. The higher your coolant protection is above 50%, the engine cooling efficiency is proportionally reduced. Secondly, use a infra-red thermoter or better yet a multimeter with the temperature attachment and check the temp ar various points, radiator inlet and outlet, engine inlet and water pump outlet. A significant temp differance would indicate a restriction between those two points. You've replaced the radiator. I assume it was replaced in-kind (4 core radiator). Holding the fan clutch blade while someone starts the engine, you should feel resistance. If not, worn fan clutch (not a highly recommended practice for just anyone). Also, visually inspect for foreign debris between the condenser and radiator that could impede air flow. Don't overlook checking the fins on your A/C condensor. Good luck,
Interesting Document. I had not run across that. According to that my truck is missing the under bumper spoiler/deflector. Wonder if I can make GM cough one up for me at no charge.

According to that GM considers 225 to be within normal operating temp as thats the temp the clutched fan and the electric fan are calibrated for.
You don't happen to have access to the images do you? When you try to view it says you are not allowed.
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Old 05-04-2008, 02:49 PM   #11
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Tom, I have seen the impeller blades rotted off the water pump. A compression leak into the cooling system is not indicated, as the temp would shoot up as soon as the load increased. The problem seems to be flow related, either water or air. A blockage would also not be indicated, it would heat up as soon as a load was put on it, rather than the other way around.
A very simple test for water flow would be to make sure the water is below the fill neck in the radiator, remove the cap (engine cool, of course), and start the engine. When it gets to operating temperature, the thermostat should open, and water should visibly flow through the radiator, from the top hose past the fill neck. You'll see water pouring out the tubes in the radiator through the side tank. If the water (coolant) doesn't flow pretty fast, or only flows when you rev the engine, you probably have a bad impeller on the water pump.
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Old 05-04-2008, 03:12 PM   #12
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not to miss any of the bases here........

many lower hoses require a spring inside to keep the hose from collapsing from the suction of the pump pulling the water at a high rate.

a thermostat that is stuck open can cause overheating if the water flows too quickly through the radiator.

it is normal for the temp. to spike after a hard run or a short rest.
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Old 05-04-2008, 07:14 PM   #13
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TSB pictures

Quote:
Originally Posted by 59toaster
Interesting Document. I had not run across that. According to that my truck is missing the under bumper spoiler/deflector. Wonder if I can make GM cough one up for me at no charge.

According to that GM considers 225 to be within normal operating temp as thats the temp the clutched fan and the electric fan are calibrated for.
You don't happen to have access to the images do you? When you try to view it says you are not allowed.
59toaster,
Most all trucks have 210 thermostats. 210 to 230 is considered normal operating range. I had to copy the pictures, so hopefully this works for you. Hope I didn't overload?
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Old 05-04-2008, 07:25 PM   #14
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OEM thermostats are 195 degree nominal opening temp. I have never seen an automobile.light truck thermostat designed to open at 210. 220 is considered to be high normal. Just like blood pressure, lower is better, up to a point. My truck overheated with a 160 thermostat installed, I put a 195 in it, and it no longer overheats.
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