350 small bock question

[Condor]

I need to pick a brain or two.

 

I have a 98 1500 suburban 5.7 Vortec that I'm having some heating problems with.

 

I had a new radiator, water pump, and thermostat installed early this last summer. I noticed that the radiator cap went on without having to push down on it. So I bought a new cap and the new one did the same thing, and I wasn't getting any pressure build up in the system. So I bent the tabs on the new cap a bit and then I got compression.

 

So now, this what it was doing. Start off in the AM and the guage will run up to 240 degrees before dropping back down to around 160-170. Then slowly rise again to about 210 and then back down, finally settling in at about 190. I'm suspecting a screwed up thermostat. Also... it had that orange coolant in the system. Actually the coolant looked clear but the cr@p floating around in the system plugging everyting up looked like rust/orange. Anyway I digress. So I took the car down to a good mechanic and they flushed the sytstem, put in fresh 'green' coolant, and installed a new HD 195 thermostat. Not an 'el cheepo' but a good one. The one that came out was caked with the orange stuff. Ugly.

 

Now this is what it's doing. It still heats up and drops back down, but not as high a temp as before, but the bottem temp is the same. Fresh coolant, new thermostat, clean system. It's still acting like a bad thermostat.

 

Now I'm thinking. Could the sensor be bad, and sending signals to the computor, and the CU is retarding/advancing the timing and causing the problem???

 

Any ideas??

[Rick Haywood]

I need to pick a brain or two.

 

I have a 98 1500 suburban 5.7 Vortec that I'm having some heating problems with.

 

I had a new radiator, water pump, and thermostat installed early this last summer. I noticed that the radiator cap went on without having to push down on it. So I bought a new cap and the new one did the same thing, and I wasn't getting any pressure build up in the system. So I bent the tabs on the new cap a bit and then I got compression.

 

So now, this what it was doing. Start off in the AM and the guage will run up to 240 degrees before dropping back down to around 160-170. Then slowly rise again to about 210 and then back down, finally settling in at about 190. I'm suspecting a screwed up thermostat. Also... it had that orange coolant in the system. Actually the coolant looked clear but the cr@p floating around in the system plugging everyting up looked like rust/orange. Anyway I digress. So I took the car down to a good mechanic and they flushed the sytstem, put in fresh 'green' coolant, and installed a new HD 195 thermostat. Not an 'el cheepo' but a good one. The one that came out was caked with the orange stuff. Ugly.

 

Now this is what it's doing. It still heats up and drops back down, but not as high a temp as before, but the bottem temp is the same. Fresh coolant, new thermostat, clean system. It's still acting like a bad thermostat.

 

Now I'm thinking. Could the sensor be bad, and sending signals to the computor, and the CU is retarding/advancing the timing and causing the problem???

 

Any ideas??

 

 

Have you pressure tested the whole system? Since you have done everything else it sure sounds like a head gasket seeping.

[Hummingbird]

if it's settling in around 190, isn't that where it's supposed to be ?? It seems all the newer vehicles run a lot hotter than the old small blocks did - 160 or so

[flb_78]

Are you going off the factory gauge or an aftermarket?

 

I wouldn't trust the factory gauge too much. It's a good reference, but nowhere near exact.

[Freebird]

That's what I was thinking. They may very well have put a 190 degree thermostat in it, that is not uncommon. So why do you think there is a problem? If the temp is settling out around 190 and the heater is still not getting hot, I would be looking at the heating system. It is possible that all that rust colored junk you are talking about has also plugged up your heater coil.

 

Although...having just read your post again. Maybe you AREN'T having problems with the heater but the running temperature of the truck.

[Condor]

if it's settling in around 190, isn't that where it's supposed to be ?? It seems all the newer vehicles run a lot hotter than the old small blocks did - 160 or so

 

Yeah, it is but it the road traveled from a cold start to get there. It doesn't just heat up to 190 and stay there.

Have you pressure tested the whole system? Since you have done everything else it sure sounds like a head gasket seeping.

The system was pressure tested while the flush was being done. If a gasket were leaking hot exhaust into the water jacket and would be causing the thing to heat up and boil over.... I think??

[Condor]

That's what I was thinking. They may very well have put a 190 degree thermostat in it, that is not uncommon. So why do you think there is a problem? If the temp is settling out around 190 and the heater is still not getting hot, I would be looking at the heating system. It is possible that all that rust colored junk you are talking about has also plugged up your heater coil.

 

I thought about that the mech stated that the flush even cleans out the heater core...

The reason I'm suspecting a problem is that it's never heated up to 240 and fluctuated like that in the past.

I just had another idea, and will check the fan clutch when I get the chance.

[Condor]

Are you going off the factory gauge or an aftermarket?

 

I wouldn't trust the factory gauge too much. It's a good reference, but nowhere near exact.

 

It's off the OEM. I'm not too worried about accuracy as much as the repeatability, and it does settle back in to the same place it always has....

[Flyinfool]

I have a '96 5.7 Vortec and it has done the same fluctuating since I bought it new in '95.

In the winter I really like the high spike to help get the windshield cleared quick.

The temp always settles out in the same place whether I am pulling a 6000 lb trailer in 100 temp or it is -20 in the winter. It is supposed to have the pink antifreeze in it not the green.

 

FWIW

I was told the the pink antifreeze avoids some of the galvanic corrosion of all of the dissimilar metals in the system, the green will let it corrode faster.

I do not know if this is really true or not.

Edited December 3, 2010 by Flyinfool

[Condor]

I have a '96 5.7 Vortec and it has done the same fluctuating since I bought it new in '95.

In the winter I really like the high spike to help get the windshield cleared quick.

The temp always settles out in the same place whether I am pulling a 6000 lb trailer in 100 temp or it is -20 in the winter. It is supposed to have the pink antifreeze in it not the green.

 

FWIW

I was told the the pink antifreeze avoids some of the galvanic corrosion of all of the dissimilar metals in the system, the green will let it corrode faster.

I do not if this is really true or not.

 

Interesting Jeff... Ours never did that until recently when I swapped out the water pump/radiator. Maybe it's finally running normal??? I thought that about the pick stuff too, but I ran green in it when we bought it used in 2001, and when I went to the pink/orange stuff things started to happen. BTW I still have the orange coolant in the '83VR.

[Flyinfool]

With the exception of the intake manifold gaskets, my entire cooling system is still original, has always had pink AF, and the AF was only changed once when the manifold gasket blew.

Thats 15 years old with over 1/4 million miles.

The AF in the radiator still looks like new and still tests as protecting to -40.

 

Now you have me thinking, is my '88 venture "supposed" to have other than the green AF in it? Mine came with the green.

[Black Owl]

Just a thought here... Have you considered the possibility of an air lock in the coolant system?

 

Not familiar with that specific motor, but on some of the newer motors they have a "burp" plug on the top of the block which needs to be opened to allow air to escape when you are refilling the water jacket. If there is an air lock in the system, it will restrict the flow of coolant fluid and you can end up running hot or get a fluctuation in the temps like you are describing.

[stroker ace]

I would think the same gunk is build up on your sensor and causing the fluctuation until it gets fully warm. Had the same issue with my 99 it was on the sensor for the fuel enrichment also so gas mileage was way down.

[93 venture]

Just a thought here... Have you considered the possibility of an air lock in the coolant system?

 

Not familiar with that specific motor, but on some of the newer motors they have a "burp" plug on the top of the block which needs to be opened to allow air to escape when you are refilling the water jacket. If there is an air lock in the system, it will restrict the flow of coolant fluid and you can end up running hot or get a fluctuation in the temps like you are describing.

Yep! or compression is leaking in system.

[BradT]

Just a thought here... Have you considered the possibility of an air lock in the coolant system?

.

 

When this happens the air from the heater system will go from hot to cold.

 

Brad

[Beau-Kat]

O.K. Here's a couple of questions and maybe a longshot thought:

 

How many miles are on the engine? You think you may have some catalytic converter pluggage?

 

I had a 1987 Ranger that was losing power and the temp was rising very quickly and falling slowly, then rising quickly again.

 

It also blew the PCV out of the right valve cover. I deduced that the catalytic converter was plugged (@ 150k miles) and backpressuring that head. With very limited exhaust being able to escape that head, it would heat up, hence my temp would heat up quickly. Then the thermostat would open and slowly bring the temp down. As soon as the thermostat closed, the temp would quickly rise again.

 

I rodded out and gutted the cat and then it ran great. Then the computer figured out that the cat was gone and it idled like crap.

 

I cured that by getting rid of the truck.

 

I now have a 2003 Z71 with the 5.3L engine @ 107k miles. It also warms up very quickly, but then stays in the normal range like it should.

 

Hope you get it figured out.

[eusa1]

Just a thought here... Have you considered the possibility of an air lock in the coolant system?

 

Not familiar with that specific motor, but on some of the newer motors they have a "burp" plug on the top of the block which needs to be opened to allow air to escape when you are refilling the water jacket. If there is an air lock in the system, it will restrict the flow of coolant fluid and you can end up running hot or get a fluctuation in the temps like you are describing.

this is a common concern with that generation of gm trucks... the reason is because the heater core is located higher in the firewall than the highest point of the radiator and allows air to get trapped in the system when repairs are performed.

yes a good gm mechanic that has a few gray hairs, will know this and have the tools to burp the air from the system "some have the bleeder " some early models do not have them.

poor mans fix??? you ask??

park your truck with the nose of the truck higher than the dash, jack it up, or park in the ditch.... then remove the radiator cap, turn on the heater at the defroster setting and lowest blower speed, start the truck and let it idle for about a half hour, and add some coolant whenever the level drops. you may have to add a few times as the air works it's way to the radiator, don't be afraid to let a bit of coolant burb out onto the ground

and if you have an hour to spare, you can be certain that all the air is gone.

put the cap back on and put it back on level ground and get back to us with your results. mike

[Shorty]

My 94 Ford six overheated so I replaced the Water Pump (one of them Blanky Blank China built junk), fixed it for a short time. While I was in Orlando for the winter my son called me and said it was over-heating again... he said you did replace the water-pump didn't you? He went thru everything including taking the head off and it still over-heated. Sooooooooooooo he pulled that Blanky Blank China built junk of a water-pump and found that all the Fins were on one side. When I got home I took it back to Advance Auto and got my money back. It ended up costing over $450 just to find out about that China crap.

 

Might be worth it to check out your new water-pump.

[snow4brains]

Sounds like a plugged heater core. It's a simple check to verify, just start the truck and let it run till the temp gets over 120 or so and then feel the heater hoses. If one or both of the hoses are cool or cold there is something blocking coolant from flowing through the heater core. And with all the gunk you're seeing in the cooling system I'll bet theres a big slug of it in the core. I know you said they flushed the system, but it's VERY common with some of the new equipment out there (read environmentally friendly) that systems don't get flushed as much as they get drained and filled under pressure.

 

Anywho, best way to flush the heater core is pulling both heater hoses at the motor/radiator, stick the hose that was warmer into a bucket and connect a garden hose to the other, and turn the hose on SLOWLY. Some city water pressure can go over 35PSI, safe cooling system pressure = 15PSI, just be careful and don't rush it. If it's plugged you'll know right away LOL you'll normally get a big old PLOP and then the water starts flowing, just let er run for a minute or two.

 

Hope this helps.

 

edit; a plugged heater can also make the gauge swing more than normal.