overheating

[JUSTIN]

my 4.3L v6 chevy truck gets too hot. new coolant, removed thermostat, new belt. only happens in the summer when the temp is over 90. stopping at a light it just starts going up. once it gets about 230 then it starts making the transmission shift late. 135,000 miles. anybody had this? I know its not a buick buts its a GM and it could be a buick. I can only think of these possibilities:<BR>1. flush radiator - coolant looks clean but I bought some flush stuff but havent used it yet.<BR>2. water pump is inadequate. maybe the waterpump I put on a couple of years ago doesnt have enough vanes<BR>3. fan clutch - since it starts to head when I sit at a light i thought maybe the fan isnt pulling enough air thru the radiator<P><BR>I posted this here since I have got all the good scoop on my riv and I trust you guys.<P>any suggestions?

[Guest]

could be a partial blockage in the radiator. let it warm up just a little and check for cool spots on the radiator. Also remove the radiator cap and start her up cool, See if the water is moving well. If you see bubbles it could be the head gasket. I'm not familar with the thermostats here but check it maybe its sticking or frozen.

[Dave@Moon]

If running the heater when the engine starts to heat up helps, then it's not the water pump. If the fan clutch isn't working the fan will be moving very slowly relative to the engine/pulleys at idle when hot, and you can check that visually usually. <P>Also, check your timing. If it is off it <I> may </I> be partially responsible. Otherwise your radiator is a likely culprit. Check the cost on a replacement at Pep Boys or Advance before committing to a recore, they're often cheaper to replace.

[JUSTIN]

i think I'll try a fan clutch. should be cheap and easy to replace? will keep you updated.<P>I have never had a radiator go bad since I stopped filling them with water. can they still gum/clog up?

[Dave@Moon]

I got a gallon of cheap anti-freeze one time at a drug store one time (store brand) that plugged up a nearly new radiator in 6 months. No amount of flushing, with or without flushing compound, woud get rid of that stuff. <P>f you have hard water where you live it could produce a precipitate that does the same thing. <P>Have you tried cleaning/straightening the radiator fins? If they (or the a/c condensor) is sufficiently blocked with bugs, etc. you could be getting the same problem.

[Guest 70 Electra]

One thing you didn't mention (I don't think) is when all this started happening. I think this might give some good clues. Did it happen gradually over several years? All of a sudden, this summer? How did the timing of the problem compare to the replacement of parts?<P>If the problem didn't occur after changing the water pump, it's unlikely that's the problem--they go bad by leaking, not by slowly degrading their pumping ability.<P>When was the thermostat last changed? They do go bad frequently, but contrary to popular opinion, the most common problem is not closing tightly, and causing warm-up issues---not overheating.<P>The radiator could explain the problem. It would result in gradual degradation. You didn't mention the year of the vehicle, but there are some service bulletins out there for 4.3 trucks that experience crudded-up radiators (a major field problem on certain years). A replacement or good thorough (professional) cleaning could fix this.<P>The fan clutch can be a problem, but usually they fail such that the fan is always on, and the car sounds like an airplane!! By the way, changing the clutch is not a particulary cheap experiment, as the quality ones are usually over $100. <P>Lastly, at the risk of the obvious, are you REALLY sure the thing is running that hot? There's a sender unit and gauge that you're relying on and although usually trouble-free, they could be malfunctioning (out of calibration).<P>Goodness knows you've got enough miles to have just about any problem, but the rad one sounds most plausible to me!!<p>[ 07-08-2001: Message edited by: 70 Electra ]

[Guest John Chapman]

Hard water? Why would that matter?<BR> <BR>You always use <B>distilled</B> water to mix with the coolant, right? If you don't use distilled water, the particulates and disolved solids in tap water will precipitate out, solidify with compounds in the coolant and muck up your cooling system.<P>Tap water will ruin batteries for the same reasons.<P>Cheers,<BR>John

[Guest oldtimer]

first off if its a new 4.3 (late 80's or 90's) then you NEED a thermostat for computer reasons (prob. a 195 deg). second no thermostat is bad also, the water moves too fast and doesn't cool properly (most race cars use a restricter plate). third, if it cools down at freeway speeds its not a radiator (look at the fam clutch). so put a new thermostat in (dealer) and check the fan clutch, thats what it sounds like if it only does it in summer.

[JUSTIN]

Its a 1993. I changed the clutch. short test drive didnt show much. I will keep you all uptodate. my basic idea is . drive it and if it heats up then get on the freeway. If it is the radiator then it shouldn't cool off. but if it cools off then what?<P>thanks guys. This is my daughters transportation and my backup when my riv is down.

[Jyrki]

Justin, if it only overheats in slow traffic, but not on freeway, your problem is inadequate flow of air or water, or both.<BR>Then, it may also be that your engine is running lean. Are you running straight antifreeze? The thermal conductivity of antifreeze (glycol) is only 1/4 of that of straight water. So a 50/50 mix is 50% worse than water. I suggest you go to Pep Boys and get a bottle of Red Line Water Wetter, and mix that with straight water. It will give you the corrosion protection, and cool down your fluid some 15 degrees. Racers use it instead of glycol. IT WORKS!<BR>On the other hand, get a Robertshaw thermostat from Summit or similar store. That's the best. <BR>Road salt and humidity will eat your radiator from the outside - check the condition of vanes, visually, or you can also tap them slightly with your finger and see if they break. <BR>You don't have undedrive pulleys, do you? Those, together with a typical water pump, are the main reason for inadequate water flow at low RPM's<BR>Let us know how it turns out!<BR>Jyrki

[Guest]

Justin,<P>Be sure to "Back-Flush" entire cooling system..not just the radiator. By an in-line flush kit(prestone makes a popular choice that works well). Connect the source water(garden hose) to the bottom of the rad, then connect the out-flow hose to the top of the rad where the cap is. You can buy radiator caps that have a garden hose connector on it. Turn on the water, then run the engine with heater on for about 20 minutes, or till water is coming out crystal clear. I have had your exact same problem before, and I never had it again after I did this.<P>Good Luck <P>Matt<BR>BCA# 34544

[JUSTIN]

well now my radiator has a pin size leak at the top so I will have to plug it . but I will try the flush and water additive. thanks all. I will keep you posted.

[NTX5467]

Many good suggestions.<P>The "only in hot weather" issue tends to point toward a coolant flow situation. It is deceptively easy for a cross flow radiator to be plugged up on the bottom areas and still look decent through the radiator cap area. Not from not using regular tap water, but from the silicates in the coolant.<P>If you need a radiator, I'd recommend using one of the composite units from a later model S-truck (of the same body series) from AC-Delco instead of a copper one. The aluminum unit has much greater heat transfer characteristics than the copper ones. Also make sure you do a OEM-style thermostatic fan clutch, not to mention that all of the factory air dams are under the front end.<P>Most of the radiator cap issues in the GM service bulletins have dealt with only the last couple of model years. There have also been some part number and configuration changes in the radiator caps themselves.<P>There are some visuals on the cap issues in a link on <A HREF="http://www.aircondition.com" TARGET=_blank>www.aircondition.com</A> to the MACS 2001 convention. They are in the presentation that GM and Texaco did on the DexCool coolant. Very informative.<P>Enjoy!<BR>Willis

[JUSTIN]

had the radiator fixed at a shop. they also "boiled" it. well now it runs cool as a cucumber. I have learned my lesson. $108 was well worth it. I will have it done on my 65 riv just for grins next time I have it down for something else.<P>the bottom line is that my radiator had clogged up using the recommended antifreeze mix. its the first time that has ever happened to me. either radiators or antifreeze has changed over the years.<P>thanks all.