There are many many people on forums talking about their 2nd gen Blazers and S10’s are overheating. This overheating condition is actually pretty common, and I’m sure most 4.3 Vortec owners, especially on the S10 platform has experienced it at least once.

If possible, I want this post to be on the “Stickies” section, because this overheating issue is pretty common now with our Blazers and S10’s being 20+ years old and many of them have coolant sludge issues due to poor maintenance.

There are so many people saying no matter what they try, the car still keeps overheating, and most answers and reply’s on forums aren’t helping them fix their overheating issues. Well, then this post is the right one for you.



This is about to be a pretty lengthy post.

Ahyhow, I have a 2001 Chevy Blazer 4 door LS 4x4 with the 4.3 Vortec that I bought earlier this year. At the time I bought it, the car had 103,000 original miles on it. When I bought it, everything seemed great, until one day I decided to sit in a parking lot with my car running. My car was overheating really bad. The coolant temp gauge was at 3/4 mark, which was when I really knew something was wrong big time.

I flushed my cooling system 4 times, which was how many flushes it took to see clean coolant inside the radiator. But 4 times of flushing did not fix my overheating issue. I even replaced the radiator cap, and the thermostat with a 195 degree stock OEM spec thermostat.

I lived with this overheating issue for about 2 months after doing the cooling system flushes.

So the next thing I tried was replacing the clutch fan. I bought a Hayden Severe duty clutch fan, just because I live in SC, and the heat is brutal in the summer. I installed the severe duty fan clutch and now the car will never ever go above 200-210 degrees even with the AC on Max in August.


So this whole time, the real issue was the original fan clutch. Maybe just replacing it with a normal duty clutch might have fixed the overheating issue. I don’t know. I definitely feel great about flushing the cooling system 4 times, even though it didn’t fix my overheating issue.

But here’s the thing! Most of the time, when your blazer or s10 4.3 Vortec is overheating, it’s probably the fan clutch that isn’t working properly or there probably is too much varnish buildup inside the cooling system that prevents optimal heat transfer.

My original fan clutch seemed like it was working great. When the car got hot, the original fan clutch did kick on, and I even heard it inside the car.

OEM stock fan clutches spin at 20-30% engagement when cold, and it spins at 50-60% when hot.

Severe duty fan clutches spin at 20-30% engagement when cold, and it spins at 70-80% when hot.

I just needed that extra 20-30% more when hot to keep my engine at optimal temp.

Here’s the conclusion.

I’m very sure that all the varnish inside the radiator and probably most of the cooling system was what caused my overheating issue with the stock fan clutch. The varnish buildup, especially inside the radiator will reduce the heat transfer, so you need more airflow to compensate for it. If I were to do the flush again, I definitely would try to get rid of all the varnish inside the whole cooling system with some strong cleaner.


So always keep up on your cooling system maintenance so the varnish never builds up!

If your 4.3 Vortec is having the same issue I was describing, try a severe duty fan clutch after getting all the sludge out of the cooling system. It’s even better if you can get rid of every varnish buildup too, but I couldn't get all the brown varnish out after using a flush/cleaning product designed for radiators.

With the severe duty fan clutch, my car still gets up to normal operating temperature of 195-210 degrees very quickly, but it will never go above 210 degrees even when I go up a steep hill or when I sit and idle with the AC on max which is what I like.

Using the Severe duty clutch is fine, because if the engine isn’t at full operating temp, the clutch will still spin at the stock 20-30% engagement, but will only kick upto 80% when needed.

Just thought I would share how I fixed my overheating issue, and I hope this post helps other people that has been having the same overheating issue I used to have.

 

Thanks for posting this.

Checking my fan clutch has been on my to do list but it has never quite gotten to the top of it. Your post confirms my suspicion that checking it and possibly replacing it us well worth doing.

This topic is one I have focused on since I use my Blazer to tow my boat where I have some pretty steep and long grades, e.g., 1,700 ft/6 miles, where it can be very hot, 100'F.

To address this I've installed an oversized all aluminum radiator and the largest Hayden transmission cooler I could find. ( Details on my build thread.) These have helped a lot as measured by my separate transmission fluid and engine coolant temperature gauges. ( an Ultra Gauge) That all said, I think my next upgrade is likely a HD fan clutch.

I think going to electric fans would work too but my replacement radiator would not accomodate them. I just today I learned that Champion Radiators has a radiator that can accomodate fans.

 

I've overheated three times due to water loss - a heater hose, the seal on the LIM, and radiator leak. Ya just gotta wait for it, it will come!