Performance loss

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Jul 22, 2006 | 10:06 AM

Red C4

Thread Starter

Racer

Joined: Apr 2006

Posts: 378

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From: Whitby Ontario

Performance loss

Just wondering were would be a good place to start.
I noticed that my '91 L98 Coupe was running a litte warmer on a hot day than normal on a hot day . I removed the Rad and cleaned out 15 years of crap.Both fans operate normally.Thermostat is recent and seems to be working . No Coolant leaks , no white smoke.
Ran a little cooler but not much ,I expected more results with the dirt I cleaned out.Cleaned and Renewed the K&N filter.

I find I have plenty of power when the engine is cool but once it reaches proper operating temps the power drops off like a rock.
I'm going to replace the EGR valve ....just because it's old.
Any thoughts on suspect items that might cause this loss of power when the engine is warm ?
This is 150,000 mile extremely well maintained L98 .24# injectors, Hypertech chip ,K&N Filter ,open breather box. Induction air foil. All these things have been on the car for three years without probs.

Any suggestions would be appreciated.

Jul 22, 2006 | 10:55 AM

FrankCandid

Intermediate

Joined: May 2005

Posts: 42

Likes: 0

From: Toronto

What temperature is your thermostat?

I'm no expert by any means but you could try a 160 degree thermostat if you don't have one.

I was running a 180 degree thermostat which I thought would be fine for my car but I had similar, less extreme, symptoms.

Mine runs real hot because of my long tubes but after I put in the 160 degree thermostat, I noticed a real difference.

For $5-$10 bucks and 20 minutes of your time to swap thermostats, it might be worth a try.

Good luck.

Jul 22, 2006 | 11:30 AM

sami85L98

Le Mans Master

Joined: Apr 2005

Posts: 8,077

Likes: 4

From: Scarborough ONTARIO

Mine does same thing, i drove 40 miles one way to work, when i close to work my vette has no power even though temp 200-210 range, when its cold it drives like a rape ape and drive like crap when its hot specially on street driving.

My whole engine is new 383/219/dart 200cc/SR intake/180 thermstat/new EGR valve........i think 160* thermostat is a good idea.

I will see if someone chime in with some solution to this problem.

Jul 22, 2006 | 12:30 PM

CFI-EFI

Race Director

Joined: Sep 2000

Posts: 17,298

Likes: 32

From: The Top of Utah

Quote:

Originally Posted by FrankCandid

I'm no expert by any means but you could try a 160 degree thermostat if you don't have one.

I was running a 180 degree thermostat which I thought would be fine for my car but I had similar, less extreme, symptoms.

Mine runs real hot because of my long tubes but after I put in the 160 degree thermostat, I noticed a real difference.

If the car was running warmer than the old thermostat temp, swapping the stat for a cooler one only serves to prolong the warm up. The stat only establishes the minimum, warm, operating temp. Once the thermostat has opened, whether at 160°, 180°, or at 195°, if the engine is running hotter than the stat opening point, it doesn't matter how little or how much hotter, the stat can have no influence over the operating temp of the engine.

RACE ON!!!

Jul 22, 2006 | 01:03 PM

GKK

Safety Car

Joined: Jan 2004

Posts: 3,783

Likes: 15

From: Northern California

The chip increases timing which would also, cause your L98 to run hotter than normal but, since you said everythings been running fine for 3 years with those parts installed, I would start with the basics with a thorough cleaning of the inside of the radiator and engine block.

Also, my "91" with stock 195* thermostat in 105* temps, reads normal (needle pointing in the center) on the temp gauge. When was the O2 sensor replaced? Your engines air fuel ratio might be on the lean side causing it too run hotter than normal.

Jul 22, 2006 | 01:15 PM

vader86

Team Owner

Joined: Sep 2001

Posts: 62,067

Likes: 1,723

From: Athens AL

C7 of the Year - Unmodified Finalist 2021

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Some dropoff is to be expected when the intake gets heat soaked, its a problem common to L98. The intake system gets hot and preheats your incoming air charge, which takes away the power you've got on cold starts. Its one of the reasons we install these lower temp. thermostats.

If you think something is up then give it a tuneup.

Jul 22, 2006 | 01:25 PM

RRT vette

Le Mans Master

Joined: Feb 2006

Posts: 8,753

Likes: 9

From: Louisiana

Quote:

Originally Posted by Red C4

I noticed that my '91 L98 Coupe was running a litte warmer on a hot day than normal on a hot day .

What kind of engine temperatures are we talking about here??

I had a 91 vette about 8 years ago that ran hot if you sit at idle too long. I didn't even have to look at the guage to tell it was hot. It started to shake a bit and when I took off it was sluggish. My secondary fan was not working and caused this.

Jul 22, 2006 | 03:29 PM

Red C4

Thread Starter

Racer

Joined: Apr 2006

Posts: 378

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From: Whitby Ontario

Thanks Guys,
I think I'll start with a General Tune up .
I'll then change the O2 sensor and the EGR just because they have not been changed in 5 years or nearly 50,000 miles.
I put the 160 degree stat in when I put the chip in but maybe I should replace it ,just because it too has been in there over 3 years.

Thanks a Lot guys , Hopefully the general tuneup will solve it.