Hi All,

A couple of years ago, I installed an L98 383 into my 86 vette and immediately experienced a creeping temp rise towards overheating.
The symptoms were that the temps always creep upwards towards overheating when idling in traffic even WITHOUT an AC.

The setup is a new stock water pump, an aluminum be cool radiator along with a robert shaw 160 degree thermostat and twin spal fans both coming on at full blast at 165 triggered by a temp switch.

The engine builder suggested that the coolant was flowing too fast and he also suggested that I restrict the coolant flow by installing a drain plug with a 5/16" hole in the lower rad hose. That helped a little bit but the temps still creeped... I varied the hole size but ALWAYS crept towards overheating. When the hole reached 1 inch in diameter, I raced towards overheating meaning it was now too big. I put back the best working freeze plug with the 5/16 inch hole in it. I can now idle at a 2 minute light and only go up 15 degrees or so. After that, I definitely feel like I should find a stretch where I can go 50 mph to let the engine cool down a bit NO MATTER WHERE I"M HEADED....

Yesterday I put in a flowkooler pump and now I can idle with air conditioning for a few minutes but I STILL creep up towards ????

When I get going again and hit 50 mph for a couple of minutes the engine cools down by a little bit but it's always fighting to overheat.. I never let it get past 205 and I end up shutting it off when it get's there.

WHAT in the world is going with this engine? Do I need a bigger water pump? SHould I get a stewart? Should I install a variable 1" valve on the lower hose to experiment with flow speed? Does timing and advance on this ecm controlled engine come into play? It is a custom chip and it had to be since the stock chip wouldn't even get the car started. 24ib injectors and a racetronix fuel pump.

Thanks to all in advance ( pardon the pun :-) )

Lee

 

You keep talking about creeping up...but what does it creep up to? Your main cooling fan won't come on until 228* F. If you turn on the air they will come on a a stop light. A temp of 230* t0 235* is normal in stop and go traffic in warm weather. A temp of 205* is just getting to a good efficient operating temperature.

 

Hi Badduck,

Both my fans are wired to come on at 165F using an external temperature switch. The ecm doesn't control em anymore. I guess I never really waited to see how high up temps would go. I'm assuming that the creep is indicative of insufficient cooling since I've heard others talk about pegging the coolant temp to the thermostat opening temp.

My main expectation is to be able to sit in traffic WITH the AC on for a good 20-30 minutes (that happens on the way to the beach every summer) without seeing "the creep". I end up focusing on the coolant temp and nothing else. I guess I want to experience a COP like heavy duty cooling cycle in the vette. I wanna idle with the AC on and windows up ( minus the donuts ....)

Thanks
Lee

 

Past threads and information on high performance engines such as yours suggest that more flow is needed, not less. You can go to a high flow belt driven water pump or an electric one such as Meseire. I would be willing to bet it would solve your problem. My DeWitt rad and 160 t-stat never runs over 185.
Bernie

 

have you verified with a seperate gauge that these readings are accurate?

 

with the 205. What bothers me is the combination you're running. A 160 stat, with a fan temp switch of 165 turning on both fans and still having it climb to 205. I think maybe the 165 switch is to low.

This is how my 87 is set up..a 180 stat, both main and aux. fans wired like yours (both come on together).....my switch is an on at 205, off at 185. As soon as my fans come on (in traffic even with ambient temps in the high 90s) I can watch temps start dropping almost immediately.They don't continue to climb much over 205..maybe 207-208. And with my stock guages I can almost see the actions of the stat.

It would seem to me with the 160/165 combination the stat would always be open and above 165 the fans would run constantly. In my mind (what little is left) you're not allowing any time for coolant in the radiator to cool down. Just a continous cycle. Could be wrong!

 

Lee,
Now I see what you are saying, but having a "mental" limit of 205* while idling for long periods doesn't seem realistic to me. In addition, I'm not sure it is possible without a major change in the cooling system design. In other words it wasn't designed to do that. It is not a good idea to stop the engine at 205* in traffic. The cooling system heat and pressure spikes up when you do that. The owners manual says to shut off and cool down at 260* IIRC.
I put a 200* aux fan sensor and a 170* thermostat in my 1989 and it will still go well above 205* before coming down. The fan cuts off at 185* so I can stay between 170* and 215* most of the time. These old cars ain't Crown Vics, good luck though.

 

Hi all,

Thanks very much to everyone for answering. I really appreciate the time you all take to try to help.

Well, the numbers are correct since I shot the t-stat housing with a temp gun and it read 3 degress lower than the car temp guage. The tuner pro program also verifies the temp guage is off by 3 degrees exactly.

I guess I'm beginning to understand the cooling cycle a little better and am leaning towards the assumption that the cycle is no longer a cycle but one continuously open coolant path like Rick said. I do see a quic temp drop the very first time I hit 163 and I guess that's the coolant from the radiator mixing with the hot coolant around the engine.

I'll try to install a 180 t-stat just to see if I get a better cycle. I don't mind higher operating temps but I really would like to see the temps stabilize and not just keep going up. Bernie I'll check to see if Mezeire makes a pump that actually fits with the right bracket hole on top etc. The thought of digging into the water pump again is scary...

I love this car and have owned it for 16 years but I REALLY regret going with a bigger engine. It seems that the original L98 didn't behave this away albeit that it had nowhere near the amount of power I now have. All this new power is useless if I'm on edge and constantly worried about a runaway cooling system.

I'm going to smoke a cigar while letting it idle in the driveway tonight to see where it actually creeps to. If by some miracle it levels off (or heaven forbid) backs down, I'll smile and just consider it fixed and myself paranoid. If on the other hand I see 230. I'll shut it off and go back to my head scratching ....

Thanks again you guys. I really appreciate the help!
Lee

 

With Rick Lambert. A 160 stat may not fully open til 170, then you have your fans on. Turn them on a little later and get that restrictor out of your system . If it were me get a good watr pump (Stewart) or a Meziere, make sure theres no debris stuck in your cooling fins on the condenser, etc. These will want to creep up a bit sitting at lights and then cool down as you get rolling, thats typical.

Wonder if youre running a little lean, have you had the A/F ratio checked? How old is that thermosta, do you know its opening all the way?

 

Lee, your expectations of driving in stop and go traffic for 20-to-30 minutes without the temp creaping up is not going to happen.

My 96' runs extremely cool and almost cold but in heavy traffic for 20-30 minutes, even mine starts to get up there (201-210). At 50 mph and above, I usually run at 170-172 until that first red light.

 

But you don't want to revert to a 180 stat and leave the fan temp switch at 165. If I were you I'd start with a higher fan temp switch.

When your system is operating properly this is how it should function.

using a 180 stat, a fan temp switch of on 205, off 185,

car warms up, at 180 stat opens, temps continue to rise until fan(s) come on in slower or stop and go traffic, temps drop back down to the 180 range. Now once cruising my temps vary between 175-180,below 180 the stat is closed and the coolant in the radiator is cooled by air, but once the engine again goes above 180 the stat opens again. The whole thing is a cycle.Hope I explained it properly?

 

Get that restrictor out of your lower hose. There is no such thing as "too much" coolant flow.

Your electric fan shutoff temp needs to be above your tstat temp. Otherwise it will still be running when the stat is shut, and never


http://www.stewartcomponents.com/tec...ech_Tips_3.htm

 

the engine temp is basically cooled by 3 methods.
1. air heat exchange by air blowing through the fins in the radiator.
1A air flowing out the bottom of the car carrying the residual heat.
2. water flowing in the block carrying the heat to the radiator, and the air carrying away the heat,
3. oil flowing around internal engine components washing the heat with it to the pan.

any of those being compromised will begin the creep, but basically, airflow over your engine surfaces, radiator fins, and the air exiting under the car and through the louvers does the most work. The water carries the heat to the radiator and then the radiator does it's thing.
The best thing you can do is take a chill pill (pun intended), drive the car through the worst traffic you can find, watch water and oil temps, and know the oil temp is serioius when it reaches 254*, and the water temp is serious when it reaches 240*. That way, you will know exactly how hot the thing gets when it's self regulated. not assisted by you on some freeway blast.
If the car never reaches those, temps,it is within it's design parameters, and you have to live with that. Remember it's not a 59 buick where 212* means a boil over and a long walk to a gas station.
There is another real factor that you have to live with also.
Fiberglass is an insulator. In saying that, you will have to remember that your hood and car body holds in the heat. The heat removing items like oil, water, and air have to be at their optimum for them to all do their jobs in keeping you cool. a breakdown of one means the others have that much more to handle.
In the summer time, low water, low oil, slow driving all create a situation that can make us unravel.
I also have an 86, and the thing runs 189 all day in 113 degree heat on the freeway at 75, but slow down to a crawl, with the air on, it stays at 215 degrees. Pick up the pace a lil, and it hovers around 200 degrees. I live in Arizona, so hot is the norm.
Oh, by the way, if it reaches 230, don't shut it off, go for a drive until it cools off

 

With that radiator and those fans you ought to be able to carry ice cream home from the grocery under your hood. When was the last time you had the radiator out for a cleaning, and to remove the debris from between the radiator and condenser? Is the engine still new? New, tight, engines naturally run hotter than normal, when fresh. The chip burner should be able to tell you where to set your base timing. Often the stock 6° (ESC disconnected) is best. Don't be afraid to let it warm up and run at a healthy temp. Your fans and thermostat are way too cool for best efficiency and engine life. Even with them set as low as they are, they are no help in stopping your temps from "creeping" to, and through the 200° mark. That shows something else is wrong. Keep looking (especially in front of the radiator) and I'm sure you'll find why your temps are "creeping".

RACE ON!!!

 

Hi again all,

Well, I let the car idle in the driveway last night with the hood closed and AC off. It took a little over 12 minutes for it to reach 230. At that point I hopped in it and dove down the street and back and it quickly cooled down to 202 by the time I got back and shut it off.

More Info
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The radiator is less than 6 months old, the condenser is brand new and there are no restrictions at all in front of the rad or between the rad and the condenser. I am now using a flowkooler water pump but ordered a Stewart from summit yesterday. I checked into Meziere and the summit guy said that they don't make an electric pump for a C4 but have a short style mechanical pump, which might work, but it won't have the threaded hole for the screw holding the emission stuff down. I decided to go with the Stewart and a Robert Shaw modified 180-degree t-stat.

I should also say that when the fans are still off, the coolant temp rises at right around 5-6 degrees a minute. When the fans come on and I'm in stalled traffic, the temps go up about 2-3 degrees per minute. What was really interesting was that as soon as I stepped on the gas, I could see the temps level off and in a couple of cases actually drop by 1-2 degrees. I attribute that to a higher flow at higher rpm's?? It's almost as if I needed help with flow at idle. The flowkooler was supposed to fix that but didn't. It might have improved things a tiny bit over the stock pump.

It's actually scary at a traffic light. I fear overheating just sitting there. I somehow think that the speed with which the coolant temp rises shouldn't be this fast. ???? How fast do temps rise in a stock 86 L98 with a stock rad and fan????

The engine is definitely tight and new (less than 3000 miles) so I can understand it making more heat but 5 degrees a minute???

I'm not sure what the air fuel mixture is and I guess I've been too intimidated to mess with timing but that's next!

What To DO
---------------

This weekend, I'll change water pumps AGAIN (Grrrr.....) and take the restrictor out and test again. Never mind that it's now in the seventies and I should be out there in the car with the top down.... I'll also check the timing. Can anyone think of anything else ???

I swear I just do NOT like seeing the 220's and above in that car. This is especially true with regards to the speed at which the engine heats up the coolant. It COMPLETELY takes away the fun and enjoyment of driving the car. It's certainly making me feel terrible about having changed the factory equation by dropping in a 383. What a Big mistake!!!!! It's sort of like re-engineering part of the car without paying any attention to everything else....I've got to figure this out. I can't sell the car... Too many memories .. Got married in it etc.

Next week I might be asking. Anyone have a stock low mileage 30-40 K L-98 with aluminum heads for sale ????

Thanks again profusely to everyone who's participating and trying to help. I appreciate it a lot y'all. Great community!!!!!!!!!!!!!!!!!!

Lee

 

Be patient - once this is solved, you won't regret the 383!