Help! 95 vette over heats when iddling

[vett-dood2]

My 95 vette started over heating when iddling but when driving down the road the temp stayed normal. The fans weren'tworking so i took it to a shop for repair. First time they told me it was ok just the heat gage was wrong.After taking a good drive and having to stop for road work it was still over heating while iddling. Took it back to the shop so they said the ecm (computer) had to be sent off for repair. I got my car back and still the temp runs high when iddling.One deference now is if the air is on the fans will run faster but off an on.
Has any one out there had the same problem and what else could be the problem? Thanks vett-dood2

 

[Hib Halverson]

Have you or the shop which does your service work run the cooling fan tests in the Service Manual?

What ECT are you seeing on the IP's digital display?

 

[vett-dood2]

Have you or the shop which does your service work run the cooling fan tests in the Service Manual?

What ECT are you seeing on the IP's digital display?

I The shop suppost to but i don't have a manual for it.
The garage spent several hrs running test. I sit and watch the heat guage climb to around 250 then the fans will come on and start cooling it down but before the ecm was repaired it would reach 260

 

[boomdriver]

You need a shop with more Vette experience...

The gauge gets its info off a separate sensor. The fans get turned on thru the ECM via their own sensor. This shop is throwing parts at a problem they do not understand.

Has anyone verified that the shroud is clean?

This sounds more like a bad sensor issue. Not an ECM...

 

[vett-dood2]

Yeah I think thats right that the shop is doing what i could have done.

You need a shop with more Vette experience...

The gauge gets its info off a separate sensor. The fans get turned on thru the ECM via their own sensor. This shop is throwing parts at a problem they do not understand.

Has anyone verified that the shroud is clean?

This sounds more like a bad sensor issue. Not an ECM...

This shop is always busy so i thought they could just diagnose an fix it but they have had it twice and had it for 3 months and iot is still not right.
I checked for obstruction around the radiator and its clean. the fans do come on now where before they didn't but don't stay on long enough to keep it cool iddling. One sencer was replaced the first time in the shop.
The ecm was sent out for repair but it didn't fix my problem. I do appreciat any help i can get with what might cause this problem. Thanks

 

[XLR8]

vett-dood2... I can't help with your technical issue but you've got excellent resources in this thread already so I just wanted to say hello and welcome to the Corvette Action Center!

Enjoy the forums!
Jane Ann

 

[vett-dood2]

Thank's

vett-dood2... I can't help with your technical issue but you've got excellent resources in this thread already so I just wanted to say hello and welcome to the Corvette Action Center!

Enjoy the forums!
Jane Ann

Thanks Jane
It's good to find other vett people are kind enough to help other vett owners solve thier problems if they can.

 

[John Robinson]

Welcome to the CAC

When you say you have watched the gauge climb to 250 to 260 degrees are you referring to the analog gauge or the digital gauge? At this point all you know is a gauge is indicating a high temperature but you have not proven that the gauge is correct. The gauge is only as good as the sensor that talks to it so you might want to find someone who understands systems and not part changing. Unfortunately too many so called mechanics want to use old school thinking when working on new school technology. In the case of the ECM it only can respond to what it is told from sensors etc. Think of the ECM as a computer. A computer requires input of information for it to give back information. Now the sensors are the source of that information and if they are running on the GI GO system (Garbage IN - Garbage Out) the so called mechanic who does not understand what is happening reaches for the most expensive and least understood part and replaces it. After all he has heard all the horror story's about these so called new fangled things and so another victim of his ignorance is sucked in and given the we can fix it as long as your wallet holds out an the parts house does not run out of parts.

Sorry for airing my pet peeve about bad mechanics. If you can find someone with a temperature reader that is hand held you might try to read the temperature around the temp sensor on the water pump and the one on the right side of the block between the back two spark plugs then you will have a better idea of what the temp is to compare to what the gauges are telling you. And while I am thinking about it has anyone pressure tested the radiator cap.

 

[Hib Halverson]

If you're going to attempt repair of this DIY, you first need the Factory Service Manual for it's cooling fan diagnostic information.

Next you need to make sure your air dam is in place and functional. Then you need to pull the top off the cooling stack and remove any debris trapped between the HVAC and the radiator.

The analog gauge on the right side of the IP is inaccurate. Use the gauges button on the DIC to put the coolant temp up on the IP display or use a scan tester to read ECT. Those are the only accurate measurement of engine coolant temp (ECT).

With the ECT displayed, start the engine with the HVAC off. When the ECT reaches 226°F the fans will come on at low speed. If the ECT reaches 235° the fans will switch to high speed.

If the cooling fans don't work in that manner, troubleshoot the system per the service manual and repair as necessary.

 

[John Robinson]

If you're going to attempt repair of this DIY, you first need the Factory Service Manual for it's cooling fan diagnostic information.


Hib I think the op is asking for ideas so they can take it to a mechanic and tell them what to check for. Great minds must think a like. Thanks for confirming my thought about a bad gauge. I think your start and idle to temp listing for the fans to kick on is a neat way to see if the system is functioning as it is supposed to . Some of us are good at working on our cars and others enjoy the car but are better as musicians, or doctors etc all of which I am not nor would I ever presume to be. If I was asked to be able to read a music score it would do me no good. For those things I can't do I search for the pros who do know how to read music or diagnose a bad heart etc. So I again welcome this new poster who is needing our expertise. As you and I both know our cars can be a learning experience.

 

[Hib Halverson]

If you're going to attempt repair of this DIY, you first need the Factory Service Manual for it's cooling fan diagnostic information.

Hib I think the op is asking for ideas so they can take it to a mechanic and tell them what to check for.

I understood that. The problem is the diagnostic charts for cooling fan diagnosis are six pages in the FSM. This is because of the complexity of the system. I want to help but I don't have the time to manually key-in all that info. The proper way to address an assumed cooling fan problem is to first see if the system works properly and if it doesn't, then go to the FSM page 6E-C12-1 and do the diagnostic. Because there are two fans, three relays and a two-step fan-on strategy, it's pretty tough to fully diagnose the system before purchase of parts without that info.

Great minds must think a like

Boy...have I got you fooled.

Thanks for confirming my thought about a bad gauge.

It's not a "bad" gauge in the sense of a faulty gauge, it's that the design is bad. The two match-needle gauges temp. gauges in the late c4 IP are inaccurate.

I think your start and idle to temp listing for the fans to kick on is a neat way to see if the system is functioning as it is supposed to . Some of us are good at working on our cars and others enjoy the car but are better as musicians, or doctors etc all of which I am not nor would I ever presume to be. If I was asked to be able to read a music score it would do me no good. For those things I can't do I search for the pros who do know how to read music or diagnose a bad heart etc. So I again welcome this new poster who is needing our expertise. As you and I both know our cars can be a learning experience.

It is a learning experience...I'll never argue with that but, part of the "learning experience" is to have a Service Manual and, when confronted with a problem (in this case, high ECTs), use the book as a starting point in the diagnostic process. IMO, that rule applies to professional service techs as well as we DIYs.

I don't have the time right now and I lack a flatbed scanner but maybe you can scan the pages in the FSM for the OP and email the images to him.

 

[captainrags]

ecm

Who flashed the ECM unit did they get the VIM # correct

 

[K & B Special Products]

Who flashed the ECM unit did they get the VIM # correct

The "VIN" would make no difference. Seriously doubt it was ever sent out for "repair" as we repair them & have never seen a temp fan control failure.