1998 k2500 454 getting hot

[newguyinnc]

Put the Autometer capillary bulb/sending unit in a "tee" fitting with the computer's temp sensor then compare the temps.

Putting an electric fan switch in the cylinder head is a great way to make the fan come on earlier.

Autometer gauges are +/- 3% over the entire range of the gauge so they are pretty accurate.

I have thought about doing this to see if the sending unit for the ECU was what was giving me a bad reading and in turn causing the ECU to give a bad timing and fuel curve leading to a lean condition. Only reason I haven't so far is that with a scanner hooked up with live data, I've confirmed ECU temp readings with a good heat gun at the intake manifold below the thermostat housing. The sending unit for the gauge is much harder to verify with a heat gun because of it's proximity to the exhaust manifold, which is why I verified it's accuracy with an auto meter mechanical gauge. (making the same test run under the same conditions with the truck and getting same results). My mechanic already hotwired the aux fan to be "key on" hot. It dropped the temps by about 10°, but the getting hot after putting a load on it still persists. Without the fan running it would run 220° down the highway, then creep up to 235° after pulling off the highway. After hot wiring fan it runs down the highway at 212-215° and creeps to just over 220° after pulling off highway. This is all with an empty truck. I used the truck to pull my dump trailer home from my shop for some yard cleanup and even with the aux fan hotwired, the truck ran 220° and when pulling up to a stoplight crept up to 235° again. I almost definitely have a flow problem or a restriction somewhere.

 

[Erik the Awful]

When the new motor was installed, the coolant was vacuum filled.

Never heard of that, and having bled thousands of cooling systems, I don't trust it as much.

The funnel shaped tool that someone posted earlier is a good tool, I use that one all the time. Turn your heater on, so you know you have coolant flow through the heater core too, then get the engine up to operating temps by holding it at maybe 2500 RPM or so, until the fan starts cycling. Then let it idle, top up the coolant in the funnel if necessary, and then blip the throttle a few times, right up to like 4000 RPM, and let it idle for a minute. You'll see some air bubbles working their way up to the radiator and out through the funnel.

Also, jack the front end up about a foot (or park on a slope). It absolutely sounds like something's keeping the coolant from bleeding properly.

Use the coolant funnel - it absolutely helps. Keep it filled an inch or two above the bottom.
Raise the front.
Turn the heater on to full heat.
Stick something in the throttle to keep the engine at 2000-3000 rpm.
Let it run until the thermostat opens, because it'll suck down more coolant after it opens.
Plug the funnel, remove it, and cap the radiator.

 

[newguyinnc]

Never heard of that, and having bled thousands of cooling systems, I don't trust it as much.


Also, jack the front end up about a foot (or park on a slope). It absolutely sounds like something's keeping the coolant from bleeding properly.

Use the coolant funnel - it absolutely helps. Keep it filled an inch or two above the bottom.
Raise the front.
Turn the heater on to full heat.
Stick something in the throttle to keep the engine at 2000-3000 rpm.
Let it run until the thermostat opens, because it'll suck down more coolant after it opens.
Plug the funnel, remove it, and cap the radiator.

I have the funnel you're talking about and did this procedure before having the engine pulled to rebuilt. I put the front of the truck up on ramps , heater on high, and sat in the truck with the door open for an hour keeping it revved up. It made no change. I'm baffled, my mechanic is baffled....we're pulling the water pump and making sure the impeller or hub isnt slipping on the pump shaft and if it isn't, we're gonna flow test the block on each side and see if there is a restriction somewhere while the pump is already off.

 

[yevgenievich]

Maybe a freeze plug that got pushed inside and got stuck somewhere in the way?

 

[newguyinnc]

Maybe a freeze plug that got pushed inside and got stuck somewhere in the way?

I doubt it. My engine man is pretty thorough and I told him when he got the motor to rebuild I thought there was something restricting flow in the block or the heads. I did have one new water mump that only lasted 50 miles because the hub came off the shaft and sent the fan into the radiator. Replaced with a delco pump, but we're still gonna pull it and remove the rear plate to make sure the impeller and hub aren't rotating on the shaft.

 

[454cid]

I just re-read most of this thread. Please verify that your coolant bypass hose connected between the water pump and intake manifold isn't kinked on the backside. Being in "good shape" so you re-used it doesn't mean it's not installed kinked.

To me it seems that you have a blockage/flow-problem someplace, as your radiator temps seem low, yet the engine is running normal to hot.

You've replaced the pump a couple of times, other than the Edelbrock that doesn't fit right, what pumps are you buying? What thermostats are you buying? Hoses?..... any chance you're getting a hose collapsing? You're installing the thermostat, spring side down, right? What about a radiator cap? It's not a Murry/Moto-Rad is it? I got a Murry that wouldn't adequately make contact inside the radiator neck so the system wasn't pressurizing.

 

[wb292]

Are you certain the water pump isn't a standard rotation pump?

 

[newguyinnc]

I just re-read most of this thread. Please verify that your coolant bypass hose connected between the water pump and intake manifold isn't kinked on the backside. Being in "good shape" so you re-used it doesn't mean it's not installed kinked.

To me it seems that you have a blockage/flow-problem someplace, as your radiator temps seem low, yet the engine is running normal to hot.

You've replaced the pump a couple of times, other than the Edelbrock that doesn't fit right, what pumps are you buying? What thermostats are you buying? Hoses?..... any chance you're getting a hose collapsing? You're installing the thermostat, spring side down, right? What about a radiator cap? It's not a Murry/Moto-Rad is it? I got a Murry that wouldn't adequately make contact inside the radiator neck so the system wasn't pressurizing.

The first was a high volume water pump, don't remember the brand name, but the hub came off the shaft in the first 50 miles. Second one was a Delco. Definitely all reverse rotation pumps. I'll check it again when I go to the mechanics after work tomorrow, but every time I've looked at it the bypass hose still has a good factory radius going into the intake. If it didn't, then I'd have cut 1/4" off the bottom of it to stretch it back straighter. Thermostats all installed spring side down. I've even cut the center section out of an old one and just used it as a restrictor before I had the motor rebuilt. Mechanic ordered a new water pump from Chevy that arrived today. Should know something good or bad tomorrow. I've had guys say they've had big blocks with cracked plenums that gave hot problems before and went away when swapped out, but that makes no sense to me. If it were something like that, then my temps at the intake should still be close to the same as the gauge if the engine circuit is flowing the way it should , not 30° different. I'm with you in thinking there has to be something restricting flow within the block.

 

[L31MaxExpress]

Late to the thread but there are two different styles of big block cooling passageways through the deck surface and matching gaskets. Mark VI vs Gen 5. Gen 6 is all together different but the head bolt pattern is different.

 

[454cid]

Late to the thread but there are two different styles of big block cooling passageways through the deck surface and matching gaskets. Mark VI vs Gen 5. Gen 6 is all together different but the head bolt pattern is different.

I think you're thinking of the 8.1l gen vii head bolt pattern.

Cooling passages are all that I think are different prior to that. Oiling for the blocks.