1993 Chevy S-10 transmission/radiator connection?

Hello! A few weeks ago, my 1993 S-10 began showing the service engine light sporadically over a couple of weeks. Then, while I was stopped and idling at a red light, the engine revved up really high suddenly for no reason. A few days later, as the automatic shifted from 2nd to 3rd it jerked a little, as if I’d tapped the brakes or something.
Around the time all this was going on, I heard something on Car Talk about the radiator and transmission being linked somehow. I checked my radiator, and sure enough the coolant was very cloudy and kinda sandy. I flushed the coolant and refilled and all the weird little transmission quirks seemed to vanish after that. Until yesterday, when the symptoms started appearing again. Any thoughts?

Since the Check Engine light has come on, the first that needs to be done is to see what codes may have been stored in the computer.

Here’s how you pull the codes from your OBDI Chevy.



I assume you have the 4.3 V6 . . .

2 possibilities . . . out of several

The transmission cooler . . . which is located inside the radiator . . . is leaking, which is causing transmission fluid and coolant to mix

The intake manifold gaskets are leaking, causing engine oil and coolant to mix

Also check the condition, (color, clarity, and smell) of the transmission fluid. If the transmission cooler is leaking, it probably will be putting coolant into the transmission…

Coolant is kinda cloudy. No weird smell. If the transmission cooler is the problem, is it something I can fix myself?

If the transmission cooler is the problem, you need to replace the radiator

Yes, you can do this yourself

And then change the transmission fluid and filter. Also flush the lines and the converter.

“If the transmission cooler is the problem, you need to replace the radiator.”

Not always. If the radiator is in good shape you can simply disconnect the transmission cooler lines and install an external transmission cooler to the radiator. It’s cheaper than replacing the entire radiator, is quick and easy to install and provides better cooling for your transmission. Win, win, win. Make sure to cap the transmission lines on the radiator when you do this.


But what if the factory trans cooler uses those quick disconnect fittings?

Aftermarket S10 radiators are plentiful and relatively cheap

Wouldn’t it be easier to just install an aftermarket radiator, and not worry about modifying anything?

I wouldn’t want to cut or modify the factory trans cooler lines, just to accommodate a cheap aftermarket external trans cooler

What if the radiator is still the original one from 1993?

That’s just my opinion

I see your point but a transmission cooler does not have to be of the cheap aftermarket variety. A decent transmission cooler can be had for little money and they offer superior performance over the OEM radiator/cooler combo. I had both a 2000 and 2001 S-10 and they both had standard connectors on the transmission cooler. I worked in the RV world for over 20 years and this alternative option was just about standard OP. Radiators do not “wear out” if they have had routine maintenance over the years.


We have 2000 and 2001 S10 trucks in our fleet, and they all have those quick disconnect fittings at the factory trans cooler

By the way, what do you consider to be “standard connectors”

I understand that radiators may not wear out . . . but the plastic tanks can crack and the tank seals can leak

I’ve noticed that about 15 years or so, those plastic tank radiators are on borrowed time . . . I mean the plastic tanks, not the aluminum cores

The standard connectors were hex head on metal tubing. The connectors don’t matter anyway because the transmission fluid coolers are attached with high pressure rubber hoses and a clamp. This is after you remove the fittings with a tubing cutter. I will agree that on an S-10…replacement of the radiator is probably a good idea since they are plentiful and pretty cheap.

How do I check to see if it’s a problem with the transmission cooler?

Pull the trans dipstick when it’s warmed up

Is the level way over filled?

Does the color look weird?

I drove it 15 minutes to a friend’s house, then checked the trans fluid with the engine running. There was nothing on the dipstick, I put it back in pull it back out and the level is in the full area. Bubbles in the fluid. The color was orange.

The trans fluid should be red

Orange might be contaminated

Does your trans pan have a drain plug?

Unless the transmission fluid is “muddy” I would suggest that checking the code as suggested already would be the next best move.

“Muddy” means thick and pasty. The consistency of spoiled milk.

It’s hard to say if you have a transmission cooler problem or not. It may be that your transmission fluid is just plumb worn out. I think what I’d do in that situation is first do a proper auto-transmission service, drop the pan, drain the fluid (sieve it to check for metal filings), then change the filter, replace the pan, then refill with fresh fluid. If that helped but didn’t fix it completely, after driving it for 50-100 miles, I do the whole thing again.

At that point you’ll know what new coolant and new transmission fluid look like. You can monitor both and note unusual changes in color, texture, or level, which might indicate a leak between the two.

Usually the way the transmission fluid is cooled is by running it through tubes in the bottom of the radiator. It may seem odd to try to cool something using a hot radiator, but the temperature of the radiator is less than the transmission fluid, so it is effective at removing the heat.

And it might be a good idea to start saving up some money for a transmission rebuild.

Ok, I’m gonna try getting the computer codes with a paperclip. I’ve read the instructions on how to do it, but I want to make sure of something first: after I’ve gotten the code, after I’ve disconnected the negative battery terminal for a minute and reconnected it, BEFORE I start the engine to get the code confirmed, is the paperclip still in the connector terminals this whole time?

I can’t get the codes if the check engine light isn’t on. And it only comes on right before the transmission starts acting funny. It has acted up in three days, and I drove it all over town yesterday. So am I right in thinking that I just need to drive it until the light comes on, pull over immediately and check the codes?

Disconnecting the battery erases codes on that truck. If the Check Engine Light comes on it will set a code and that code will remain in the memory for quite a while even if the light goes off if you don’t disconnect the battery.

To get the codes turn the key off, insert the jumper, turn the key on but don’t start the engine. Watch the light and count the blinks.