Ok what i have is a 92 rs with a carb 350.

When i purchased this car it was pretty rough, lots of wiring issues from the po and hokey set ups. It would overheat fast after ignition 260 in 2 min.

I replaced the radiator, hoses, water pump, thermo, thermo housing, intake mani and fans. fan set up is dual electric with a flip switch, rad is alum 2 core, thermo is 185.Temp gauge is aftermarket set up. All hoses are oem from gm.

Here is the issue. When driving city it runs 200 to 210 no big deal, when running highway it runs 190 to 220(temp has been checked and is dead on)

Now when i run on the highway and then go to city the temp keeps climbing to 240 245.

The fans seem to do nothing to cool it down, the only thing that will help is to shut it down or get back on the highway. It vap locks all the time after getting hot also.

The one thing I have noticed is when the motor gets warm around 200 and up my oil pressure drops to between 0 and 25 at an idle (aftermarket gauge) when i give it gas it does go up to 35 to 50.

I did take it in to a mech and have him check the compression, head gasket is good(according to him)

Any ideas here?

 

Fans pulling through the radiator?

 

Yes the fans do pull.

 

Sounds kinda like maybe the fans have their polarity reversed, like they are pushing the air back through the radiator once they turn on. Also I would check your ignition timing.

 

Second the ignition timing. Was the distributor replaced when the FI was removed?

 

Distributor was replaced upon fi removal, Had timing checked when i had a strting issue a month ago and was told it was dead on. Motor itself runs perfect no issues at all except the cooling problem when coming off highway.

 

As far as driving-- do you have the air dam?
For the fast overheating-- flush the cooling system.

Just a thought.

 

All right here is a bit more info, took it in to the shop for a looksy. They checked compression,timing, coolant system pressure, fan flow, thermo, hoses, flushed system and changed coolant. No problems found.. Do have air dam also.

The one thing that was pointed out to me is that my fans are set back about 3/4 of an inch from the rad. He suggested that maybe that gap is causing the fans to pull air from around the rad instead of through it. Does this sound possible? It kind of makes sense to me. The only problem I see with that is there is no other way for them to hook up without modifications.

Any one deal with this before?

 

That may be an issue, but instead of putting the fans all the way against the radiator, what about making a shroud for them? the other thing, is the space between the condenser and radiator clear? you didn't accidentally get the wrong rotation water pump, did you? At this point, it seems like you shouldn't have a problem anymore, or at least found the cause.

 

In short, no.

Lets use some common sense for a sec. In 1991, Would GM have produced the car with fan's that were "3/4 inch" away from the rad if they didn't work to cool the vehicle? Again, No.
Would they have put a fan shroud on instead of mounting them like they had if it needed one. Yes. Remember, a fan shroud works both ways, restricting/channeling flow.
I say this because your car should cool from natural air flow while moving. Fans should only come on while stopped/moving slowly (under ~35-40mph)

Not striving to get on your bad side here, just something to think about.
A stock cooling system is setup to cool the OEM engine setup. You have added a 2 core Alum radiator to your mix, which should only help. What has been done to the engine?

2 things cause overheating (on an otherwise stock system)
1) lack of coolant flow (stat not opening, pump is weak/worn out/installed wrong/reversed flow, ports are clogged)
2) lack of air flow through the radiator (fans not working/air dam not installed or installed incorrectly, radiator fins are all bent over)

 

I have not had a chance to do anymore digging on this issue yet but I was able to talk with a gm mech about it for a while today.

Keoman- He agreed that the fans should be fine.

What he did suggest was that maybe it has all to do with my oil, using 5 30. He suggested maybe the oil is just getting to hot and losing to much viscossity. Told me to try a heavy weight oil for the summer and that may shed a lot of the heat issues.

Also he made a suggestion that i could add a fan to the front of the radiator blowing in since I have all that extra space.

Now that in mind he said there is no way to tell for sure unless i brought it in for him to tear into and it could be something else entirely.

Anybody think the oil idea is a possible candidate for the problem?

If that doesnt crack it I think i will put on the extra fan and then tear into it this winter and start over.

As far as what has been done to the motor I only know for sure what i have done and then what the PO says was done.

Motor was removed old 5.0 replaced with a 5.7 from 89 formula.
PO claims complete rebuild. Was def rebuilt but I don't believe with all the performance parts he claimed.( i knew that going in and was ok)

What I know for sure:
Fuel injection was removed is now carb with holley 600 cfm, and aluminum intake.
Msd ignition(distibutor,wires, ect....)
Hedman headers with Borla cat back
New rad,hoses,water pump,serp,thermo housing,temp guage, Alt,starter,

This motor does put out pretty good power for a 5.7 though trans is old and does not keep up.

The car did sit for almost 3 years before I bought it -hence the complete coolant system overhaul.

 

Couple things that come to mind to check:
Timing. I'm no carb expert but on a buddy's 79 Caballero with a mild 355, we run at 34* Around 3000 RPM's. Good power output but no cooling issues. Burning extremely hot as well as a light weight oil mixed with summer heat may amount to your problem.

While its on my mind I would ask you how long this problem has been going on? Have you owned this car in colder temperatures? IE 50-70* Did it react the same?

Just re-read your original message again and loosin oil pressure at idle also suggests your oil is thinning badly with the heat or your bottom end is very tired. Personally I run full synth 5/30 in the 95*+ heat here And don't loose pressure on a stock bottom end of an L98 with over 200k miles. But it depends widely on how it's been treated.

Fans: I think you said they were added on, each fan needs to have its own 30 amp relay circuit. Power wire and ground should be at least 14AWG.

I'm no expert, just throwing somethin out from my perspectives.

 

Thanks Keoman,

I have had the car for some cooler temps, bought it in December and at that time it wouldnt cool at all. garaged it and replaced cooling system. I brought it out in the spring and at that time it did pretty good. It seems to be if temps are below 80 it does wonderfull, still will get 210 to 220 but thats not too bad. At night on the highway when its around the 70s it will run from 180 to 210 depending on how i drive. When the sun is out and the temps are up it will hit 245 on the guage.

I think I am going to have another look at the timming and see if anything changes and i will be doing the oil change out prob next week.

oh and the fan set up came on it. I just fixed the po's back asswards wiring.

I am thinking there may be something to the oil issue, not sure if that will solve it but I will change it and add the extra fan on front and see what happens.

Thinking that i really need to tear this motor down and see for myself how she sits. I hate not knowing how and exactly what was done!!!!!!!!!!

I will let you all know what i come up with next week when I crack back into it.

 

Get a 3 row aluminum rad. A 2 row will NOT cool a 300hp motor. As far as the thicker oil goes, I'd be worried about your bearing clearances. Go too thick and the oil can't get into the cavities it needs to, to lubricate everything. I would say no more than 10-40.

 

I should have done a 3 row when i replaced everything else (Hindsight) I do have that in future plans, though they may end up being sooner than expected.

I was curious as to what adverse reactions a thicker oil may have in this motor and the gm guy told me that if its running that hot it should thin it out enough to be fine.

I don't really like should and maybe. I like will and will not!

But yes I am planning to try the 10/40 first and if that works great, if it helps but still has trouble i may go up a bit more. The 15/50 mixed with 5/30 that he suggested seems a bit thick. I'm sure a some gm engineer would blow a gasket hearing a gm mechanic offer that up.

But hey gm engineers also came up with the whole dex cool idea.

 

Update###
I had a bit of time to tinker with the car today, the first thing I found while going over the cooling system again was my lower hose sucking shut when the motor revs. hmmm that was a brand new hose yay.. So i took off the old hose and decided to flush out the motor again.

There was a lot of nasty junk that came out and this was the third flush since purchase.

I went for a new hose and discovered that the hose i got from gm does not have the coil in it to keep it from collapsing nor do any of the hoses available at the local parts stores. I took a cheapo hose and put it on to test and it collapses at 2000 to 3000rpm in park.

Where do I find a hose that will not collapse? I think this stupid hose is the core of all my cooling troubles.

 

Ok found a guy at Oreilly auto parts that knew what i was talking about with the hose. He said they don't make them with the wire anymore because the new materials should not collapse??? Well i have two brand new hoses that collapse under rpms.

Anybody have a line on a good hose?

 

www.cjponyparts.com

They have the stainless steel lower radio hose springs.
Cut to fit & all is good

 

Sweet! Thank You for the info. I just ordered it.
I am also going to check out the local plumbing store and see what they have for future use.

I do feel a bit funny buying something from a pony shop, but I need what I need.

 

On another forum, a guy said it would work for a small block chevy.
I need 1 too but have to wait til I get some gremlins out of the wire works : (

 

My hose is from work (oreilly) and I've never noticed it collapsing, even with a brand new water pump.

 

Don't worry too much about buying stuff from a pony store, they have been putting LS engines into their cars.

 

It's Alive!!! Kinda....

Changed out the bad hose with a gates vulcan and no more collapsing issues. Flushed out the motor 3 more times and put it all back together.

Took it for a run last night after i finished i ran it hard on the highway and then on the street and it never got over 205. Ran it to work this morning also 45min hwy and it stayed right at 195 to 200.

After work on the way home it ran 210 hwy and then when i got off on to the street it got up to 235. Grrrrrrrr.......

So still running a bit too hot but moving in the right direction.

Have the heavier oil to put in yet and will try some water wetter then see what it does.

 

Age // condition of radiator cap?
Have you tried a new one?
Recovery tank working?
Just wondering if its all good.....

 

I replaced the cap with the radiator, it seems like it's holding pressure (hence when i pull the vent tab it vents very strong) thought that does not mean it is working perfect.

overflow seems to function fine.

One thing I'm going to check is the t stat, i put in an old 195 last night instead of the 180 i had in it. Possible problem.

Also ran water in the rad so i didnt waste more $$$ on coolant in case the repairs didnt work.

As soon as I get time this week I will pop in another 180tstat and fill with 50/50 and water wetter, then try the heavy weight oil.

Can't wait to get this cooling deal done so i can start throwing $$$$ at something fun, like some nice new tires or maybe some new interior!!!!!!

 

The 180 tstat won't make a difference for engine temperatures above...180.

Don't expect significant improvement from the use of the WaterWetter.

The lower rad hose can collapse from a high flow water pump or missing t-stat. It is also more likely to collapse at higher rpms, which doesn't fit your initial description of the problem?

 

Id hold off on the 50/50 coolant till you get your problem fixed or winter shows up. I run bout 10 hotter on 50/50 water wetter vs straight water.

 

I run a 70/30 mix in my car. Antifreeze/water. No additives.

 

Alright.... This is a love hate relationship turning to more hate than love.

Put on a new rad cap this morning and put in some purple ice, drove it to work again to test it out.

Ran perfect this morning once again 190 195 the whole way on hwy and only went to 200 on street. Outside temp this morning 67f.

Whole different story on way home. jumped up to 210 before getting on hwy(about 1.5 miles and 3 stop lights) After getting on hwy it ran at 210 for about 20 miles then started climbing and topped at 235. On the street 1 mile from hwy to home it kept climbing to 250. Boil over into overflow as i pulled in the driveway. Outside temp 88 to 90.

Will go through the basics once again and see what it is I'm missing.

 

I think I've figured out how to fix the problem. Just don't drive home from work! lol

 

Seems as if you have covered the basics pretty well, might want to look into the non-basics.
IE bad water pump/clogged head ports/pinched radiator cores.

 

Another update###

Played with the car a bit today, put the old rad cap back on and took it for a drive. I stopped by the local shop and asked if one of the guys had time to take a ride with me and check it out.

We took it on the highway (temp today 97) I expected it to start climbing very fast but to my suprise it didn't..... The temp got up to 220 then down to 210 then up to 215 then down to 200??? All over the place. Mechanic kicked on the heater at full blast and it was blowing cold then hot then cold then really hot.

What we ended up putting together was this:
Climbing up hill the temps drop by 20f and the heat cranks
Going down hill the temps climb 10 to 20 and no heat
On straight flats the temp climbs very slow but never comes down and the heat goes in and out

We decided it was gremlins and Burned the car. Jokes!

Anyway it has an air gremlin in it that refuses to come out so I am going to take it to a local 90 degree hill in hte morning and try to burp it out. If it doesnt come out I will take it in to his shop and let him do it.

One way or another by tomorrow night it will be cooling, I'm done with this prob and ready for the next.

Thnx for everyone's help you guys all rock!

 

And..... It's done!!!!! Cooling at nice 195 to 200 on a 97f day running around town for 40 min.
Very Happy gremlins are dead

Put it on a 90 degree incline and opened up the rad with the heater on full blast. After about 5 min it climbed up to 240 and ran there for a few min,then all of a sudden some steam came out and the radiator practically emptied into the block. I added a full gallon of 50/50 before it finally stayed full.

Also while I was watching the second fan came on and guess what? The darn thing was pushing air not pulling. So now it is wired to pull.

So this one is solved. And numerous people suggested a blockage and fan prob from the start. I'm not suprised that it slipped past me since I'm new to this but I spent a bit of money at the shop having them look at it and they told me fans where fine and that system was flowing properly. Time for new back up shop.

 

Great!!

 

A small hole drilled into the tstat will help prevent air pockets within the cooling system.