1999 Suburban Overheating

[RogerMcP]

Hello all,

I have been reading posts on this site for some time and enjoy all the expert advice that users and mechanics give other users. I have never posted before, but now I'm hoping that someone might know where I should go with an overheating problem that just started.

I have two 1999 2500 4wd Suburbans that I use for my work. Both are identical and are equipped with the Vortec 7400 (L29) 454 ci motor. As mentioned they are also 4wd and 3/4 ton. One has about 170k miles and the other has about 140k miles. All of a sudden the one with 170k miles has developed an overheating issue. If I'm driving around town it will get much hotter than normal (have not hooked a scan tool up to see the exact temp of "normal, but the needle on the temp gauge always used to rest on (or very near) the heavy mark to the left of the 210 degrees F mark). Around town, or on the freeway at speeds around 40 to 70 MPH, the needle will usually NOW come to rest right at, or a bit to the right (hotter) of 210 degrees F. If I'm towing a 3,500lb trailer, which I often do for work, it will keep rising (especially if the A/C is running) all the way up to the point where the "Check Gauges" lights up on the dash (around the heavy mark to the right of the 210 degrees on the gauge). At this point I have always shut it down and called for the other suburban to take over towing. Also, it may be important to know that every two years I have the radiators drained and refilled (they call it "flushing", but I don't think they actually backflush anything) by a local shop as part of routine maintenance.

I do not know much about auto repair, but am okay working with my hands. Thus, a friend who is a retired mechanic said that I should 1st check the fluids in both the radiator and overflow. I did and all check out just fine, then he told me to "burp" the system and gave me instructions on running the vehicle with the heater on and so forth. No change noticed. Next he told me to remove the thermostat (just for a test, not to leave it out) and plug the bypass (so all the fluid will go through the radiator). I did that and have found that the problem is still there, but appears to be a little bit better. It seems to take longer to climb into the hot zone and did not get hot enough to light the "check gauges" warning light. However, since this was a test tow it was a bit shorter so I don't know what would have happened if I kept going, I'm assuming that it would not have stabilized but probably would have kept climbing. Anyway, my friend now says that it might be the "fan clutch", but that I should speak to someone who knows GM vehicles better. Thus, I'm now posting...

I'd greatly appreciate any advice from you gurus as to what to do, or what to check next! My friend has a scan tool and says that I can borrow it if need be, I have not recently (many years now) seen the "check engine" light lit (in other words it is not currently on).

Thanks!
Roger

[TexasT]

Might be time for a new radiator. I don't know what your have be putting into the radiator as coolant but if the water is like mine it isn't good and has a lot of minerals in it. These can settle out on the bottom of the radiator. This lessens the ability for it to cool. I only use reverse osmosis water and coolant in mine to try to prevent this.
Also the water pump might be getting worn. The impeller might have some wear and isn't moving enough coolant.

Are you checking the coolant level before you start the truck in the morning? It could be low. I know mine has a radiator with the plastic end tanks. These tend to leak after a while and could cause a low coolant problem.

Let us know how you make out.

[Dr_Zero]

To check the clutch fan its pretty simple WITH THE ENGINE OFF give the fan a little spin it should not be too easy to spin or keep spinning.

If its spins pretty easy like then it probably needs replacement and when it comes to replacement you usually have some options you can get the standard one, the heavy duty and the severe duty model. The severe duty is for towing or for motor homes.

It looks like they list only the sever duty for your truck runs around $85

[L0sts0ul]

Hey texas, you and me keep meeting like this LOL.

I agree again with TexasT, I live in canada, and my temp goes from -40C to +40C in a year so what Im going to tell you is strictly if you live in a +5C and above environment.

I would check your water pump, I agree with hard mileage, and the size of that motor, the impeller could be worn, or a busted fin in general.

HOWEVER there are a few quick easy checks to see whats going on.

First, Check your fan belt, make sure its not too cracked or stretched...(you'd be surprised what a belt can screw up.

Next, check to see what the flow out put of your radiator is. Buy a rad flush kit from your nearby auto store (easy to use) and flush your system completely till the water runs clear.

Replace the thermostat, with a cooler range one ( you won't get as much heat from your heater core, but it will help keep the engine cooler.

At this point you HAVE to make sure your radiator is actually flowing though or the rest of this is useless.

You mentioned you did a lot of driving with AC, make sure your ac is fully recharged.

now the tricky part. IF you are in a warm temperant climate, you can get away with a 80/20 or even 90/10 water to antifreeze mixture. HOWEVER, the water has to be DE-MINERALIZED WATER. this is not the cheapest part but its the best.

This is a start... all of this should be less that 100 bucks really. its all good maintenance to practice every 1 or 2 years anyways.

Hope this helps.

[MrShorty]

One thing I haven't seen mentioned, yet: air flow. You say you've had the radiator drained regularly, and some have suggested checking water flow through the radiator. Definitely good ideas. Another thing I'd check would be air flow through the radiator. Make sure you haven't got a bunch of leaves/dirt/crud blocking the grill, nothing has gotten between the condenser and the radiator. Just need to make sure there is good air flow through the radiator.

[L0sts0ul]

One thing I haven't seen mentioned, yet: air flow. You say you've had the radiator drained regularly, and some have suggested checking water flow through the radiator. Definitely good ideas. Another thing I'd check would be air flow through the radiator. Make sure you haven't got a bunch of leaves/dirt/crud blocking the grill, nothing has gotten between the condenser and the radiator. Just need to make sure there is good air flow through the radiator.

Good point ^^ I missed that.. lol, that a great idea...

[RogerMcP]

Thanks for all the good info guys! I'll respond trying to keep with the order which I received replies...

TexasT: I understand about the new radiator and our water is very hard out here too. However, the radiator shop claims they do not use tap water because of it (don't know exactly what they use, I'd need to call). We have an RO unit at my work with a 15 gallon tank, I could easily use RO water if needed. Is there anyway to check the impellor without removing the water pump?

Dr_Zero: Thanks for the useful info regarding checking the clutch fan. What I came up with is that (with the engine off) the fan turns pretty easily. However, it will not keep spinning and there is a little tension on it (not much). Trying to think quickly, I did the same test with the other suburban that we have and it appears as though they move with the same amount of ease. Since that suburban's cooling system is still working well, I'm inclined to think this must not be the problem, do you think I'm on the right track?

L0sts0ul: I'm assuming that there is no way to check the impeller without removing the water pump? As for the fan belt it is a serpentine belt, was replaced somewhat recently (don't remember exactly, but it appears to be in good shape and does not have any cracks). I think this means that it is ok, but please correct me if my attempt at logic is incorrect. I will take your advice and purchase a radiator flush kit (they appear to have them at the local auto store) -I'm hoping to get that done today. As for the thermostat, at the moment it is completely out and I have removed and plugged the bypass line from the water pump to the intake manifold. When it comes time to put one back in I do not have any problem using a cooler one, but before this problem the temperature never moved much at all it always ran exactly where it did from the factory (including when towing -we never tow in overdrive). You also said to check the A/C and it is fully recharged and working perfectly. As for de-mineralized water, can I use the RO (reverse osmosis) water that I mentioned above since we have a 15 gallon tank here at work? Glad to hear you think the repair will be cheap, we obviously take having two of them for granted as we are really missing this one while it is down!

MrShorty: Actually this was my mistake, I forgot to mention that my friend (the retired mechanic) told me to check that right at the start (you two are thinking alike) and the air path is very clear. Also, I should mention that he also told me to check the radiator cap to make sure that this one did not go bad and was building up unnecessary pressure. I did not know how to check it, so I swapped them between suburbans without any change in temps to either one.

Ok, I think I'm down to flushing the radiator after purchasing a kit to do so and then if that does not work, checking/replacing the water pump. Do I have this right? Anything else that anyone can think of????

THANKS FOR ALL THE VALUABLE INPUT!
Roger

[RogerMcP]

An update:

I got motivated and purchased the pressurized back flushing kit and went through the procedure as described in the directions. The fluid was very clear and very green. We did not notice much come out of the system that should not have been there. I have re-filled the radiator with a 60 / 40 mix of RO water / antifreeze.

Unfortunately, the problem still exists! Do we all agree that next up is the water pump? Can I test it without removing it? If I need to remove it, how do I test it, or is it better to just replace it? Any other ideas?

BTW, I should have mentioned that the fluid is always full and is not leaking out. As far as I can remember it is the stock radiator, and if I'm reading the posts correctly, I guess it has plastic tanks, but no fluid is leaking even after 170k miles.

Thanks,
Roger

[97chevz71]

[L0sts0ul]

trolling? lol j/k

yeah RO would work fine I believe, and I always suggest a colder tstat in warmer environments where you don't usually use heat.