Sorry this is so long, but it seemed to all be relevant information.

Okay, all of the searches I do have revealed many threads from C4 owners who are concerned because the main fan does not seem to run as they believe. The standard answer is that the temp will rise to 229 or so then the fan comes on and it cools down to the 190's.

That is how my C4 behaved until about 2 weeks ago.

Driving home from work one night (200 miles round trip)the temp as i was approaching home was rising and when it passed 230 I was worried. I have the main fan wired to a switch to turn on when I want it on. Turning it on made no difference. The temp was 250 when I pulled into the garage.

When I popped the hood the system was so pressurized my son and I were almost thinking a hose would burst.

That weekend I decided to flush the radiator, change the thermostat and put in new Yellow coolant. I drove it locally for 50-100 miles and it behaved as normal.

Monday when I drove to work as I pulled into the lot the temp went past 229 again up into the 230's. Before I left that night I checked the fluid levels and all seemed good. After about 70-80 miles the temp started rising as I was cruising at 65. 220, 230, 240 I shut it down and coasted to a stop, let it cool down and then went another few miles before the temps topped 250. I shut it down coasted to a stop and waited 1/2 hour. At that point the water temp was down to 182. I started the car and was able to drive the remaining 20 miles. When I pulled into the garage it was at 250 again, and seemed to be really pressurized.

There is no indication that it is a cracked head, block or a gasket. The oil is good, no coolant or foam when I look into the valve cover access.

I decided to change the waterpump but as a precaution I pulled the radiator and took it over to my local radiator shop. The disassembled the tanks from the core and boiled it out, saying it was 80% clogged. The water pump appears to be fine and there is no weeping/leaking or noises coming from it.

I replaced the upper and lower hoses, replaced the radiator and all the coolant with more new coolant. I put the front end on the ramps to raise it up. We filled it burped the system as recommended here on the forum. 3x and it seemed good

I have the same problem today.

This morning all the way across the desert it ran at 186 and seemed to be operating normally. As I approached LA the temp started to go up but this time it did not seem so out of control as before and never got above 240. But it still seems like there must be some issue I am missing.

The heater/defroster was turned on it's highest setting when I refilled the radiator, the front was raised, the expansion tank was filled completely. There is no leaking after the car is stopped, there is no leaking in or on the engine that I can see, but I did notice that at lunch today I had to add about 1 qt to the exansion tank before I went to lunch. I operated normally in stop and go traffic and when I sat in the drive through.

I really could use some constructive hints if anyone has any on what this issue is. I can find no previous threads or posts that outline this type of problem.

Wish me luck, I need to drive the 100 miles home and hope that I don't have to pull over too many times.

 

A couple of things don't sound right. First a year would be good information. I have to assume that when the radiator was out, that you cleaned between the condenser and the radiator. I find it strange that cleaning an 80% blocked radiator didn't make a bigger difference. Hopefully now you know that flushing and changing the coolant on schedule is a good idea. You didn't mention it early on, but the later comment, "I did notice that at lunch today I had to add about 1 qt to the exansion tank before I went to lunch." makes me think you are at the early stages of a blown head gasket.

RACE ON!!!

 

Unless i missed it, did you replace the thermostat and cap? Also, not for sure if putting the yellow stuff in was a good idea or not? Assuming you ment dexcool, if it came with the green stuff you probably shouldn't have switched to the yellow.

 

I understand the 'yellow stuff' is green stuff, except it is bittered in CA.
Good questions though.

Any sign of leakage or hot A/F odors?

 

This is not a stupid question but is your fan wired to PULL air or could it be PUSHING ? You mentioned you had a switch which means the wiring was altered as a minimum.

Ground your ALDL (jumper the top two terminals with a paper clip) then turn the key to on but don't startr the car. You r fan(s) should run.

Put your hand behind the fan. If you don't feel air rushing at your hand, you may have wired the fan backwards.

Good luck

 

Check the foot well on the pasenger side under the carpet. If it is wet with AF your heater core has a leak.

 

I'm with CFI-EFI, I think you need to start testing for a blown gasket. I fought with wierd cooling issues for months (even installed a DeWitts) until I finally admitted it was head gasket. My symptoms were:

No white smoke
No cloudy oil or oily coolant
losing coolant (i.e. overflow tank emptying as the system cooled, expansion tank getting lower over time)
Occasional episodes of FULL overflow tank (on long journeys)
(and this is the kicker) - a bubbling noise in the overflow tank with the engine off - sure sign of exhaust gas in the coolant.

Because you mention that the system seems pressurized I would rule out a pressure cap, but they are cheap and probably worth replacing just as a trial.

Good luck - on the bright side a blown head gasket is a path to many worthwhile mods!!

 

I unfortunately concur with the diagnoisof CFI-EFI as well. Guess I just wanted to hear it from owners who may have had similar experiences. It makes sense that the car can be drive short distances of 60 miles or less with no problem but after the heat from the exhaust gases has a chance to adversely affect the coolant.

Well at least all of the cooling system except the waterpump and heater hoses is new. Glad I waited to do that WP last.

The car is an '89 coupe/auto. I bought it 3 months ago and have put 10,000 + miles on it since then. It has 173,000 miles on it now.

I flushed the entire system a week ago when I replaced the coolant. The cap is new, the thermostat is new and drilled. The heater core is new. The entire front of the car is completely debris free, especially easy with the radiator out.The fan is wired correctly. The problem is a matter of airflow. The fan comes on when it is suppoed to at 228-229 degrees. It is wired correctly throught the fan relay to pull through the radiator.

At idle turning on the fan will pull the temp from 220 down to 183 in a matter of minutes, it is only on there when I first got the car and did not understand how the system is designed to function and was freaking out at stoplights and in traffic when the temp climbed above 200 degrees.

The fan is irrelevant at speeds over 30 or so miles per hour. In fact at speeds above that having the fan on can impede the airflow more than assist it.

Thanks for the tips!

 

When my own 1991 had head gasket problems she was dumping coolant out the radiator cap. The garage test for carbon monoxide in the coolant was positive so the head gaskets were replaced. It may be worth getting your local garage to test for carbon monoxide in the coolant to see if the head gaskets are on their way out. Ecklers do a kit part number 40415 which makes the fans come on at 185 c which would help to keep the engine cool and stop you worrying about the temperature

 

Ray posted my suggestion, I was reading this last night around midnight and decided to forget about it until morning.

Ray handled it for us. Have the coolant checked

Just a General FYI...... I'd like to add that just because you may not get white smoke this does not mean that your head gasket is not blown. It just means that super heated gas is only going into the coolant system and no coolant is able to leak back into the combustion chamber after shut down.

 

Since the Vette has a 60 mi range I will drive it over to the shop this weekend.

I am pretty sure it has a blown head gasket. One additional clue I forgot to add was the overflowing foamy coolant in my expansion tank when shutting down after the hi temps, it looked like someone put in Mr. Bubble.

I am wondering though if at this point rather than just replacing the head gaskets if I should rebuild the whole motor. I can do the head gaskets this weekend but the rebuild will take a little longer.

The car is drivable and runs good. As long as you don't mind stopping every 60 miles to let it sit for 1/2 hour to cool off.

She still hasn't left me stranded or had to go on the hook so I'm happy.

When I bought this Vette I expected to have to spend this money, I was just surprised I got 10,000+ miles out of it before spending.

 

Also suggest testing for a head gasket.

 

All C4 radiators were a single row (1"tube) aluminum core with plastic tanks. These radiators are so inexpensive that no radiator shop would invest the time to doctor a radiator that is basically a throw away. I wonder if the radiator hasn't been replaced at some point with a less effective copper radiator with brass end tanks. This is the type of radiator a shop would un-solder and rot out.

Another common problem with C4 (90-96 mostly) is over filling the system and as a result, ballooning the flat tubes to round. This will in turn crush the fin, and block air flow completely. The coolant flow test will pass perfectly but zero air will go through the core. The obvious telltale sign of this problem is the top and bottom rail will be curved, not straight. You also will not be able to slide a zip tie through the core.

 

I'm with Tom

First change ou that old POS radiator......

I have one of Tom's and they are fantastic.

If you can't afford one of his just put in a wholesale replacement from Rockauto or one of the other wholesale radiator companies.

Then let us know what happens.

At speed your temps should drop like a rock, unless your radiator fins air flow is blocked.....sounds like that's the case and it is a very typical symptom of C4's.....

 

The radiator that is in the car is a Modine, 1" core single row with plastic tanks on each end. The radiator shop I took it to said that they pulled off the tanks, rotted it out, them reassembled the tanks to the core. The passenger side tank shows evidence of balloning from normal indicating appearant high pressures within the system.

There seems to be adequate spacing between the fins, I will try the zip-tie test.

I would much rather spend a few hundred on a good radiator if the head gaskets are not compromised.

I really think it has a blown head gasket but I will try any suggestions anyone has if it means kepping her on the road and not in pieces in my garage.

 

you could allways try some copper block seal

 

I may be disecting your words, but you can't balloon a plastic end tank. If you do, it cracks and it's done.

 

That's just the way the radiator guy described it. When he did I kind of thought exactly like you but we can't always all communicate on the same level especially here in Southern California.
He was a nice guy though.

Anyway there is a huge difference now in the flow through the core as opposed to how it flowed before he did whatever he did.

At least from a visual perspective as the temps rise when I am filling the thing up.

I really think the entire cooling system is operating very close to how it is supposed to, the engine just has a problem.

When I opened the expansion tank in the garage after the temps peaked as it was overheating and there was extensive foaming in the expansion tank when at the overheated system

In your experiences doesn't that indicate an internal sealing problem in the engine such as a head gasket or in worst case a fracture of the head or block?

 

The Modine is an excellent OE replacement. You made a wise purchase when you bought that. Beware of cheap replacements and hyped up multi row copper/brass replacements. It takes multi rows of copper/brass to equal the cooling of the stock, 1 row, aluminum radiator. Don't buy a non-aluminum radiator for a C4. If the stock or quality stock replacement won't do the job, and the rest of the cooling system (head gaskets included) are in good shape, then the the DeWitt 2 row all aluminum radiator is the best solution. Few people need them, and they are expensive, but there is no better alternative in those cases.

I got a similar, "it's shot" story on the second plastic tank I had replaced. I took the radiator in because we suspected a trans cooler problem. It turned out to be something else, but in the meantime, I got sold a replacement tank. The first tank, years earlier, had a leak.

RACE ON!!!

 

The foaming is due to the surfactants in your brand of antifreeze. Used for De foaming

http://en.wikipedia.org/wiki/Surfactant

Please, have a shop check for Hydrocarbons in the antifreeze.