1992 Blazer Cooling Issues

MI0706 · 12-21-2007, 05:17 AM

Hello all... I'm new here and was hoping that some of you could give me some advice on my cooling system. I have a 1992 Blazer Sport with a 350 CID engine.

About a month ago, I noticed that when my Blazer is heating up from cold, the temperature gauge will climb to the 215F/230F range before it starts regulating (the weird thing is this is when I'm driving at approximately 40mph or higher, if I'm going under that speed, it will climb to the 230F range). If I let it idle the entire time during warmup, it will climb to the 230F range and stay there permanently until I drive it.

Once either of these ranges are hit, it will stay there for approximately 30 seconds and then dive back down to the 195F range and regulate normally. It will continue to regulate normally even if the engine is turned off and started back up (while it is still warm, if it is allowed to cool down, it will go through again what was previously mentioned).

I also noticed that the radiator had a leak during this timeframe. So, in the last month, I've changed the thermostat (195F), the radiator cap (16 psi), the temperature sensor, the radiator, and the drive belt. Next month I will be taking it to a shop to have the cooling system flushed (I'm only doing this because I do not know when it, if ever, was done).

I've only had the vehicle for two months and I never noticed the temperature gauge doing this until 1 month ago.

Is this normal? Should I be looking at the water pump? The fan clutch?

MI0706 · 12-21-2007, 07:49 PM

wow... not one single reply...

Hayden · 12-22-2007, 12:11 AM

Try another temp sensor and check the wiring.

crabtruck · 12-22-2007, 02:35 AM

welcome to the forum MI0706.
Nice to see an EE that likes trucks.
Seems it would have been a good idea to flush system while you had everything open.
Oh well... could be the flow is insuficient for the t-stat while at low rpms.
So maybe looking at restriction but I'm thinking more the pump is going.

MI0706 · 12-26-2007, 01:19 PM

crabtruck: I agree, I should've went ahead and did a flush while everything was open.

I was thinking about insufficient flow at low rpm's as well. But the one thing I can't get my head around is that after the "initial" heat up, the temperature regulates normally (while driving and idling, never going below 190F and never going above 200F).

Hayden: I don't think it's the temp sensor. This is the second one. The previous sensor was doing the same thing. Now, it could be a wiring issue. However, why does it only do this on the "initial" heat up and then show normal from then on?!?

I don't know, it's got me confused. I was hoping that someone else here had a 92-94 Blazer just so I could compare with them.

Thanks for all the replies.

75K30 · 12-26-2007, 02:45 PM

I think you have air in the system. A pocket of air that stays in the engine can cause hot pockets or even turn to steam. Is that 16 psi cap the right cap? Have you tried to run the engine up to operating temps with the cap removed? I believe you are getting proper flow, and the syatem seems to be working well, it just has a small variable that seems to be related to having the system open.
You should see the system "burp" with the engine running and the radiator cap off when the t-stat opens. Would imagine that you will even have to add some fluid after it "burps".

MI0706 · 12-27-2007, 04:56 AM

75K30: Thanks for the advice. I did not think of that.

So, let me get this straight... Take the cap off. Start the engine, let it idle, and warmup. Watch it to see if some trapped air comes out (burp). How high do I let the temperature go before shutting off the engine (meaning, if the engine gets up to XXX amount and still hasn't burped, shut it off)? Keep in mind, the last time I let it idle on an initial warmup, it went to 230F and stayed there.

As for the cap, that is the pressure rating of the one that came off of there. The book calls for a 15psi. Locally I could only find a 16psi cap. I called the local Chevy dealership (service department) and they said that a 16psi would be fine. You think I should find a 15psi via the net?

MI0706 · 12-27-2007, 05:31 AM

The cap that I have is a safety cap that has the lever on it (allows venting to the reservoir). Instead of taking the cap off and potentially losing coolant on the ground, can I let it vent to the reservoir while trying to "burp" the system?

75K30 · 12-27-2007, 09:23 AM

You culd try just lifting the lever, but this method does not allow you to visually confirm that air is actually being let out, nor does it allow you to watch the level change as the t-stat opens.
How hot do you let it get? Well if the system is working properly, it will not overheat, and will reach operating temps safely. You will spill some fluid, and will more than likely have to add some to top it off, or at the very least add enough fluid to take the place of the trapped air. This may be a little, and could be quite a bit. Would be willing to gamble a little here, and say that when the t-stat opens, the tank in the radiator will empty out quite a bit. More than you can add to just the recovery bottle. This would explain why the problem continues to exist. As you add coolant to the empty radiator, it will be much cooler than the engine and can cause the t-stat to close, so allowing it to once again warm enough to cycle the t-stat open again will be necessary. A candy type, or meat thermometer stuck in the filler neck is a good tool here.
The 16 lb cap should be just fine.

MI0706 · 12-27-2007, 12:15 PM

75K30: Thanks for the advice. I will try this and see what happens.

12-21-2007, 05:17 AM	#1
MI0706 Senior Member Join Date: Dec 2007 Location: Crawfordsville, Indiana Posts: 84	1992 Blazer Cooling Issues Hello all... I'm new here and was hoping that some of you could give me some advice on my cooling system. I have a 1992 Blazer Sport with a 350 CID engine. About a month ago, I noticed that when my Blazer is heating up from cold, the temperature gauge will climb to the 215F/230F range before it starts regulating (the weird thing is this is when I'm driving at approximately 40mph or higher, if I'm going under that speed, it will climb to the 230F range). If I let it idle the entire time during warmup, it will climb to the 230F range and stay there permanently until I drive it. Once either of these ranges are hit, it will stay there for approximately 30 seconds and then dive back down to the 195F range and regulate normally. It will continue to regulate normally even if the engine is turned off and started back up (while it is still warm, if it is allowed to cool down, it will go through again what was previously mentioned). I also noticed that the radiator had a leak during this timeframe. So, in the last month, I've changed the thermostat (195F), the radiator cap (16 psi), the temperature sensor, the radiator, and the drive belt. Next month I will be taking it to a shop to have the cooling system flushed (I'm only doing this because I do not know when it, if ever, was done). I've only had the vehicle for two months and I never noticed the temperature gauge doing this until 1 month ago. Is this normal? Should I be looking at the water pump? The fan clutch?

12-22-2007, 12:11 AM	#3
Hayden Senior Member Join Date: May 2006 Location: Bay City,Michigan Posts: 383	Try another temp sensor and check the wiring. __________________ There Is No Replacement For Displacement

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12-21-2007, 07:49 PM	#2
MI0706 Senior Member Join Date: Dec 2007 Location: Crawfordsville, Indiana Posts: 84	wow... not one single reply...

12-22-2007, 02:35 AM	#4
crabtruck Senior Member Join Date: Jul 2007 Location: on your 9 Posts: 3,366	welcome to the forum MI0706. Nice to see an EE that likes trucks. Seems it would have been a good idea to flush system while you had everything open. Oh well... could be the flow is insuficient for the t-stat while at low rpms. So maybe looking at restriction but I'm thinking more the pump is going.

12-26-2007, 01:19 PM	#5
MI0706 Senior Member Join Date: Dec 2007 Location: Crawfordsville, Indiana Posts: 84	crabtruck: I agree, I should've went ahead and did a flush while everything was open. I was thinking about insufficient flow at low rpm's as well. But the one thing I can't get my head around is that after the "initial" heat up, the temperature regulates normally (while driving and idling, never going below 190F and never going above 200F). Hayden: I don't think it's the temp sensor. This is the second one. The previous sensor was doing the same thing. Now, it could be a wiring issue. However, why does it only do this on the "initial" heat up and then show normal from then on?!? I don't know, it's got me confused. I was hoping that someone else here had a 92-94 Blazer just so I could compare with them. Thanks for all the replies.

12-26-2007, 02:45 PM	#6
75K30 Senior Member Join Date: Jul 2006 Posts: 2,992	I think you have air in the system. A pocket of air that stays in the engine can cause hot pockets or even turn to steam. Is that 16 psi cap the right cap? Have you tried to run the engine up to operating temps with the cap removed? I believe you are getting proper flow, and the syatem seems to be working well, it just has a small variable that seems to be related to having the system open. You should see the system "burp" with the engine running and the radiator cap off when the t-stat opens. Would imagine that you will even have to add some fluid after it "burps".

12-27-2007, 04:56 AM	#7
MI0706 Senior Member Join Date: Dec 2007 Location: Crawfordsville, Indiana Posts: 84	75K30: Thanks for the advice. I did not think of that. So, let me get this straight... Take the cap off. Start the engine, let it idle, and warmup. Watch it to see if some trapped air comes out (burp). How high do I let the temperature go before shutting off the engine (meaning, if the engine gets up to XXX amount and still hasn't burped, shut it off)? Keep in mind, the last time I let it idle on an initial warmup, it went to 230F and stayed there. As for the cap, that is the pressure rating of the one that came off of there. The book calls for a 15psi. Locally I could only find a 16psi cap. I called the local Chevy dealership (service department) and they said that a 16psi would be fine. You think I should find a 15psi via the net?

12-27-2007, 05:31 AM	#8
MI0706 Senior Member Join Date: Dec 2007 Location: Crawfordsville, Indiana Posts: 84	The cap that I have is a safety cap that has the lever on it (allows venting to the reservoir). Instead of taking the cap off and potentially losing coolant on the ground, can I let it vent to the reservoir while trying to "burp" the system?

12-27-2007, 09:23 AM	#9
75K30 Senior Member Join Date: Jul 2006 Posts: 2,992	You culd try just lifting the lever, but this method does not allow you to visually confirm that air is actually being let out, nor does it allow you to watch the level change as the t-stat opens. How hot do you let it get? Well if the system is working properly, it will not overheat, and will reach operating temps safely. You will spill some fluid, and will more than likely have to add some to top it off, or at the very least add enough fluid to take the place of the trapped air. This may be a little, and could be quite a bit. Would be willing to gamble a little here, and say that when the t-stat opens, the tank in the radiator will empty out quite a bit. More than you can add to just the recovery bottle. This would explain why the problem continues to exist. As you add coolant to the empty radiator, it will be much cooler than the engine and can cause the t-stat to close, so allowing it to once again warm enough to cycle the t-stat open again will be necessary. A candy type, or meat thermometer stuck in the filler neck is a good tool here. The 16 lb cap should be just fine.

12-27-2007, 12:15 PM	#10
MI0706 Senior Member Join Date: Dec 2007 Location: Crawfordsville, Indiana Posts: 84	75K30: Thanks for the advice. I will try this and see what happens.