Author Topic: 91 Suburban over heating question  (Read 3728 times)

Offline Deercreekfarm

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91 Suburban over heating question
« on: September 07, 2019, 05:28:52 PM »
So the temp started rising on the burban. Noticed a small leak in the radiator so replaced it with a new one. Still no change, replaced thermostat and no change. Replaced the fan clutch and again no change. Yanked of the water pump went to get a new one and nothing matched it. Everything for a 91 v2500 4x4 6.2 Diesel did not match. Finally a pump for an 85 Suburban fit. Problem now is small leak from between the face plate and the engine. Yank it off, wipe everything down, new gasket, bolt it back on multiple times and still a small leak.

Anyone had this problem? Any tricks or secret fix?

Also now I have to track down the VIN on the engine block and figure out whatís going on with only the 85 water pump matching up. Only thing I can think is previous owner replaced engine block and put all the 91 electronics on it.

Offline MIKE S

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Re: 91 Suburban over heating question
« Reply #1 on: September 07, 2019, 06:44:16 PM »
91 is reverse rotation. 85 is standard rotation. Make sure it matches your set up

Offline Deercreekfarm

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Re: 91 Suburban over heating question
« Reply #2 on: September 07, 2019, 09:35:13 PM »
91 is reverse rotation. 85 is standard rotation. Make sure it matches your set up

Yeah like I said now I have to do some research because when I picked up the 91 water pump from the parts store it looks almost the same as the one that came off the engine but the internal channels look a little different and the bolt pattern is different. So we tried an older one 85 and it matched perfect to the pump that came off of the engine.

So Iím thinking the previous owner swapped motors or is there a chance that the front plate (not sure of actual name) that the water pump bolts to then that plate bolts to the front of the engine, is there a chance these are interchangeable over multiple years?

But then again I was having an overheating issue before so Iím at a loss.

Offline Deercreekfarm

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Re: 91 Suburban over heating question
« Reply #3 on: September 10, 2019, 10:01:49 PM »
At a total loss!!!!!!   

New thermostat, new radiator, new water pump and sheís still overheating. Does anyone have any ideas or suggestions?

Could a clogged heater core make the engine overheat?

Offline Irish_Alley

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Re: 91 Suburban over heating question
« Reply #4 on: September 10, 2019, 10:23:34 PM »
warped head or blow head gasket would cause it to overheat. if it ran out of coolant and over heated it might have did more damage to it. my cummins had an overheating problem but it was blowing coolant out of the overflow tank. never replaced anything trying to troubleshoot it. unhooked the turbo and drove it without any boost and it was gutless and i was on it easy but it didnt overheat. replaced the head gasket and no more problems. take the rad cap off and start the truck, do you notice bubbles in the coolant when the engine is running? let it warm up with the cap still off and look for bubbles. normally the coolant will have some bubbles due to the flow but you might notice more than normal amount of bubbles. also a bad rad cap will cause it to overheat
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Offline Deercreekfarm

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Re: 91 Suburban over heating question
« Reply #5 on: September 10, 2019, 10:33:35 PM »
warped head or blow head gasket would cause it to overheat. if it ran out of coolant and over heated it might have did more damage to it. my cummins had an overheating problem but it was blowing coolant out of the overflow tank. never replaced anything trying to troubleshoot it. unhooked the turbo and drove it without any boost and it was gutless and i was on it easy but it didnt overheat. replaced the head gasket and no more problems. take the rad cap off and start the truck, do you notice bubbles in the coolant when the engine is running? let it warm up with the cap still off and look for bubbles. normally the coolant will have some bubbles due to the flow but you might notice more than normal amount of bubbles. also a bad rad cap will cause it to overheat
Thanks for the info. I will check that out.

Offline Deercreekfarm

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Re: 91 Suburban over heating question
« Reply #6 on: September 21, 2019, 08:58:03 PM »
Update.............. 9-21-2019

After flushing the cooling system and installing a new radiator, new water pump, new t-stat (180), radiator cap and a new fan clutch and bleeding off all the trapped air  the old girl is still overheating.

When I take off it will climb up to red line for a couple of seconds then fall back down and while driving freeway speeds temp rarely gets over 180. When Iím idling or driving in town temps climb up. Thought maybe it was  a bad t-stat off the shelf so yanked it and ran it straight through no t-stat but itís the same thing.

So now Iím thinking itís the dreaded HEAD Gaskets leaking!!!!!!!!!!!!! No coolant in oil, no leaking coolant anywhere and to be honest no real loss of coolant. She just gets hot and pushes all the coolant into the overflow bottle and fills it up. Almost like theres too much pressure in the engine and itís keeping the coolant from cycling through the engine and just pushing it into the overflow bottle.

When I flushed (multiple times more than 10) the water is cycling through the engine fine but when everything is put back together she over heats.

Does this sound like head gaskets going or am I missing something here?

Offline JohnnyPopper

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Re: 91 Suburban over heating question
« Reply #7 on: September 21, 2019, 09:27:07 PM »
From your description you have a Diesel.
Sorry to sound ignorant, but is there a way to test compression on a Diesel?
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1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
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Offline Deercreekfarm

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Re: 91 Suburban over heating question
« Reply #8 on: September 21, 2019, 11:11:05 PM »
From your description you have a Diesel.
Sorry to sound ignorant, but is there a way to test compression on a Diesel?

Yes itís a 6.2 Diesel and I can test the compression on it. Like I mentioned I think the head gasket may be leaking and causing pressure to build up in the radiator and push everything to the overflow bottle. Just wondering if anyone else had experienced this or knew a little more than me before I go tearing down the top end of the engine.

Offline VileZambonie

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Re: 91 Suburban over heating question
« Reply #9 on: September 22, 2019, 07:33:49 AM »
Get yourself a combustion leak test kit. Any auto parts store should carry one suitable for diesel. If it identifies positive, then the next thing to do is remove the cylinder heads and inspect. Check for warpage, cracks and obviously a blown head gasket. You should definitely try to get a positive ID on your engine.
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Offline JohnnyPopper

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Re: 91 Suburban over heating question
« Reply #10 on: September 22, 2019, 04:46:48 PM »
So a combustion leak test will show you if any hydrocarbons i.e. diesel fuel or byproducts of oxidized fuel are in your cooling system.

Since you flushed yours so many times, it should show up plainly if indeed your heads/gaskets are the issue.

What is Bizarre is that you run normal on the freeway...

Earlier in your thread, Mike mentioned the two years are reverse direction from each other.

Did you check to see that your fan belt driven components are turning clockwise?

If the combustion test is negative, I would look at the long shot that your water pump is going the wrong way.

If it is, it would make sense that your getting hot from a reverse flow of hot water, not up through the cooler block into the hotter head surfaces.

More likely the heads are the issue. Can't see GM make such a vulnerable possibility, but wait....
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Deercreekfarm

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Re: 91 Suburban over heating question
« Reply #11 on: November 03, 2019, 05:56:57 PM »
So a combustion leak test will show you if any hydrocarbons i.e. diesel fuel or byproducts of oxidized fuel are in your cooling system.

Since you flushed yours so many times, it should show up plainly if indeed your heads/gaskets are the issue.

What is Bizarre is that you run normal on the freeway...

Earlier in your thread, Mike mentioned the two years are reverse direction from each other.

Did you check to see that your fan belt driven components are turning clockwise?

If the combustion test is negative, I would look at the long shot that your water pump is going the wrong way.

If it is, it would make sense that your getting hot from a reverse flow of hot water, not up through the cooler block into the hotter head surfaces.

More likely the heads are the issue. Can't see GM make such a vulnerable possibility, but wait....

You are correct the 91 6.2L do have a reverse water pump. When I ordered the new on it looked nothing like the one I took off of mine. Turned out I had to order an 85-87 water pump so obviously itís not the engine that came with the truck. Another tell tell sign is the VIN is a J code burban which I believe were all serpentine belt driven, this engine has 3 separate belts.

UNLESS; there is a way to remove the front plate off of the engine and install an older plate and pump. Then I guess they would have changed out the serpentine belt which I couldnít see why anyone would do that so my guess is they dropped another (earlier model) engine in it.

Well hereís the update; doing head gaskets now so next weekend the wife and I will take it for a road trip and see how it does. If itís running good then I will start looking into doing the lift, tires and paint job.

Iím trying to find somewhere near NC or SC who builds custom roof racks.

Offline JohnnyPopper

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Re: 91 Suburban over heating question
« Reply #12 on: November 04, 2019, 03:44:08 PM »
Better have a spare vehicle just in case...dead truck + mad wife=deadly combo :-[
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Irish_Alley

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Re: 91 Suburban over heating question
« Reply #13 on: November 04, 2019, 06:16:13 PM »
Better have a spare vehicle just in case...dead truck + mad wife=deadly combo :-[
this is why i try to keep 4 vehicles on the road at all times. this way even if one goes up and funds arnt there i can still risk loosing another vehicle and theres no rush to fix the broken vehicle on the weekend or call offs from work
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When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Deercreekfarm

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Re: 91 Suburban over heating question
« Reply #14 on: November 04, 2019, 07:25:09 PM »
Better have a spare vehicle just in case...dead truck + mad wife=deadly combo :-[

Ainít that the truth!!!!!