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Old 05-04-2008, 06:35 PM   #15
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Thermostats

Terry;
When I first started turning wrenches, we had 180 thermostats, then with more emissions came the 195 and now GM has 210. Just sharing my experiences. However, the shop service manual is the bible.
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Old 05-04-2008, 09:20 PM   #16
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Quote:
Originally Posted by lsinclair
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?
Thanks for posting those. Looks like the only one that will apply to me and the original poster is the chin spoiler. I'll see if I can get the dealer to work on it. Considering my company bought 30+ trucks through them in the last couple years I might be able to get a little help.


As for the Thermostat..... I know factory my R series 1988 454 Suburban is 195f as is all the R and V series 350 and 454 trucks 87 through 91.

I could see the newer miltiport injected Vortec's running something different. Lets not forget the rated temp of a thermostat is its full open temp. A 210f Thermostat would be partly open by 195f. The higher temps does help lower emissions and the newer motors are regulated more then the older ones.

This however does not apply to the posters vehicle. His truck is a 84 454cid C 20 Suburban with a Rochester Quadrajet if its factory.


From what I can tell the 84 was 195F factory and if it has the ESC and mixture control carb It should stay with that. If it has an aftermarket carb and a normal HEI distributor then a 180f would probably be OK but I wouldn't go lower as it may not allow the EGR to function properly. That will raise NOX and engine temp.
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Old 05-05-2008, 04:28 AM   #17
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Great responses

Thanks, everyone, for the ideas.

To followup a little on some of them, a Stant-brand thermostat was originally in place when the trouble started. But since I thought it was my radiator giving me the problem, the thermostat was replaced with a new, 195 degF Stant thermostat. I forgot to mention the radiator cap was also replaced.

Later, like about two weeks ago, I went down to the GMC dealership and bought an AC Delco, 195 degF thermost. After pulling the Stant out, both the OEM & Stant thermostats were brought to a boil in a pot of water to verify cracking temperature. Both thermostats passed. The AC Delco thermostat was then installed in the motor.

My Suburban is, like 59toaster mentioned, a 1984 model and it has lots of miles. But since the compression is good, it seems unlikely to me that age is the issue.

It does have the factory oil cooler, and thanks to Overlander63 (from a year or two ago), that cooler has new lines going to it. And the lines get hot, so I figure the cooler is funtioning.

My engine does have a Quadrajet, but no knock sensor, or any electronics on the carb.

The spring is in place in the lower radiator hose.

Interesting comment about pink versus green coolant. Yes, I am running pink coolant in the Suburban. Doing so means I only have to keep up with one type of coolant. I never thought it could cause an over heating problem.

Thanks, lsinclair, for that bulletin. "Impellor slipping on shaft" caught my eye.

In reading and talking to others, I found out race cars don't have thermostats per se. Those cars have orifice plates in place of thermostats. Apparently, the system needs a little bit of back pressure to keep the pump from cavitating. A disk with a hole is better than no thermostat at all.

If I decide that the thermostat is still my problem, the plan is to gut the old Stant thermostat and mount the resulting orifice plate.

I wonder if I have too much clearance between the water pump's impeller and the block?

Tom
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Old 05-05-2008, 06:05 AM   #18
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you've covered and recovered almost everything i can think of, except the fan clutch. you stated that the clutch engagement coinsides with the drop in temperature. could it be that the cluth should be slipping at idle?

is there a fan shroud on these vehicles?

has anyone replaced the clutch with a flex fan on these vehicles?
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Old 05-05-2008, 02:26 PM   #19
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Thanks for elaborating 59toaster. Good points one should be aware of.
Ricky also mentioned the fan clutch (and I agree). I mentioned a method for checking the fan clutch in a previous post here. Given the year, make, model (K2500?) and the lack of emissions for this vehicle, I would strongly suggest checking or having the fan clutch checked. As a loose rule of thumb, if you see an oil residue on the front of the fan clutch, you've lost fluid and the clutch may not be functioning as designed. As a side note, I don't recommend purchasing the so called blue light special parts. If the part does not meet or exceed the OEM spec, I would refrain from purchasing that part. Lastly, should you go to a shop, have someone who can do diagnosis and avoid the "parts changer". Unfortuantely, there's too many parts changers in the automotive field. Some lack the proper equipment to diagnosis and proceed on guess work or past experience...all at your expense!

PS; Quadrajets are a good carb. With high miles, one area to pay attention to is the throttle plate where the primary shaft goes through. If excessive play is noted, it will impact idle and MPG's.
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Old 05-05-2008, 02:38 PM   #20
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Quote:
Originally Posted by lsinclair
... Ricky also mentioned the fan clutch (and I agree). I mentioned a method for checking the fan clutch in a previous post here. Given the year, make, model (K2500?) ... Quadrajets are a good carb. With high miles, one area to pay attention to is the throttle plate where the primary shaft goes through. If excessive play is noted, it will impact idle and MPG's.
Larry,

The fan clutch is brand-new, and operates like I think it should.

The last one lasted about three years before leaking all it's silicone fluid out and doing nothing but freewheel.

The one before it seized on my Overlander's first trip.

My Quadrajet has the throttle shaft play you mentioned. If I could find a decent machinest AND new bushings, I would fix it. Care to recommend anyone?

Thanks for your insight - I do appreciate it.

Tom
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Old 05-05-2008, 03:18 PM   #21
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Interesting reading

Quote:
Originally Posted by TomW
...Interesting comment about pink versus green coolant. Yes, I am running pink coolant in the Suburban. Doing so means I only have to keep up with one type of coolant. I never thought it could cause an over heating problem...
Forum member ROBERT CROSS replied to a PM I sent him about DexCool:

Quote:
... Probably the biggest mistake people make with antifreeze is the mixture. It needs to be a 50/50 mixture, without the proper amount of water a straight mixture will not cool properly.

http://www.consumeraffairs.com/news0...m_dexcool.html


Autoblog

...
Anyone have anthing to add?

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Old 05-05-2008, 04:37 PM   #22
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Quote:
Originally Posted by TomW
Anyone have anthing to add?

Tom
Just that the impeller on the water pump is a couple of inches from the block, with a steel plate on the back of the pump. I would think if the impeller were slipping, it would do so more at higher engine speeds, as there would be more resistance to movement from the natural viscousity of the coolant.
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Old 05-05-2008, 04:50 PM   #23
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Quote:
Originally Posted by TomW
Forum member ROBERT CROSS replied to a PM I sent him about DexCool:



Anyone have anthing to add?

Tom
That PDF link posted recommended a 44/56 antifreeze/water mix caught my eye.

I had read a good coolant article many years ago in Car & Driver and it had a lot of good info about Red verses green and mixtures including a 40/60 for warmer climates.

One thing I remember about that article is NEVER put Red in an older vehicle.

WOW! its still online!

Good read I thought and some of the gear heads here might be interested.
Red Verse Green
Top it Up with Green? Or Orange? Which Antifreeze? - Column/Patrick Bedard/C/D Staff/Columns/Features/Car and Driver - Car And Driver

Mixtures and older vehicles.
Dr. Turcotte Writes a Few Coolant Prescriptions. - Column/Patrick Bedard/C/D Staff/Columns/Features/Car and Driver - Car And Driver
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Old 05-05-2008, 04:54 PM   #24
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Quote:
Originally Posted by overlander63
Just that the impeller on the water pump is a couple of inches from the block, with a steel plate on the back of the pump. ...
That's a nice way of saying that I confused my Burb's water pump with another one of my vehicle's water pumps.

You're right, Terry. A Suburban water pump has a backing plate.

I noticed my mistake after the editing period was over, and hoped no one would notice.

I forgot about you....

Tom
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Old 05-05-2008, 05:36 PM   #25
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Quote:
Originally Posted by TomW
That's a nice way of saying that I confused my Burb's water pump with another one of my vehicle's water pumps.

You're right, Terry. A Suburban water pump has a backing plate.

I noticed my mistake after the editing period was over, and hoped no one would notice.

I forgot about you....

Tom
The same thing happens to me at work, when I have a senior moment and hope no one notices...Inevitably some one does.
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Old 05-05-2008, 05:54 PM   #26
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radiator

have you checked the radiator for blockage ? you have hit on everything but that.A BLOCKED RADIATOR STILL SHOWS FLOW HAVE A hand held heat sensor movineing along the rad checking the temp from top to bottom and side to side.on that year vechile with milage you can expect some blockage. it happened to my truck and I change my antifreeze evey 2 yrs.had the rad recored and no more problems.boiling it out weakened the core on mine thats why the recore.
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Old 05-05-2008, 09:24 PM   #27
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GM TSB's on Overheating

Quote:
Originally Posted by TomW
Larry,

The fan clutch is brand-new, and operates like I think it should.

The last one lasted about three years before leaking all it's silicone fluid out and doing nothing but freewheel.

The one before it seized on my Overlander's first trip.

My Quadrajet has the throttle shaft play you mentioned. If I could find a decent machinest AND new bushings, I would fix it. Care to recommend anyone?

Thanks for your insight - I do appreciate it.

Tom
Tom;
I checked for all applicable TSB's on '84 model w/7.4 engine for overheating.
There are 3 TSB's (Technical Service Bulletins). They include pictures which for some reason don't open up in PDF format (?). I'll break this into 2 posts as follows; this post has 2 PDF's. One is a supplement to the other. Both have the same illustrations, so I won't duplicate. I would give serious consideration to an add-on GM electric cooling fan (part # in TSB) as this is an identified problem that relates to your symptoms in your 1st post.

As far as the Rochester Quad goes, I would suggest a machinest that has worked with aluminum and have some brass bushings made to fit the throttle plate/shaft. The only other quad issue has been the power valve has been known to stick in the down position resulting in noticeable loss of power. #0000 steel wool takes the scoring out of the brass valve restoring free up and down travel. No parts needed providing the air horn gasket isn't damaged.
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Old 05-05-2008, 09:42 PM   #28
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TSB Overheat part 2

Tom;
Here is the last TSB, which you should read first. Take note of the dates of each TSB. Before I spent any $, I'd verify good airflow through any coolers, condenser and lastly the radiator. There should be no debris causing any restriction. Per this TSB, I wouldn't worry about casting flash. With high miles, head gasket deteration would be a last resort possibilty. Hopefully this wil provide some direction for a cure to your woes with minimal expense.
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