O.k. Folks,

I have a overheating problem at speed (65+ MPH). Doing a search on overheating, my problem is not uncommon. Several posts mention changing out the fan clutch to solve the problem. Without going into my details, I just need a couple of questions answered.

1. Has anyone solved overheating (say speeds higher than say 50 MPH) problems by changing out the fan clutch?
2. Has anyone had an experience with overheating caused by too much flow through radiator? (had owner of radiator shop mention this as a possible problem)

Thanks

 

At normal temps how fast does the clutch fan stop when you turn the motor off?
At highway speed you should get enough air flow to keep your engine temps in line.
A few questions, what motor and what rear gears?
Do you have a chin spoiler?
Lower radiator hose with a spring in it?
Are all the seals around the radiator in place?
What thermostat?
How hot is hot and have you confirmed the temperature with an IR gun?
Have you changed the temp sensor?
A little more information will help. PG.

 

My chin spoiler was so soft and old that it would deform when in high-way speeds, I removed it and put Indy spoiler instead, now whan I drive my car in high-way the electric fans never goes on no matter what the ambient temp. is.

 

Yes, check if the lower radiator hose isn't collapsing at high revving speeds. Check thermostat opening. Some of them can close partially with high water flow. Choose a high flow thermostat that will open widely ( MILODON, Mr GASKET,... ) and will stay open under high pressure / high flow circumstances.

 

To answer Petes74ttop questions.
Fan turns about 2 revolutions after motor is shut off when gauge showing 200-205 F.
Motor is stock L-48 w/3:55 gears (runs about 3100 RPM @ 70 MPH)
Chin spoiler is in place
Lower radiator hose is suppose to be new style that doesn't need spring, however I transferred my old spring from previous hose. I have also checked for hose collasping with engine at speed.
Seals are in place
Standard 180 thermostat -new-checked and opens fine
Radiator is new, brought back to check for solder blockage and is fine.
Running hot for me is anything over about 220.
Checked with IR - Gauge showing about 180 and temps showing 185 w/IR so don't suspect gauge.

Problem started when I changed radiator from what I call 3 row to a 4 row style.
car would run 180 all day no matter what speed I was running or ambient temp was.
Sending unit and gauge have not been replaced, but I don't suspect them since only change was radiator and how closely the IR readings match the gauge display
I have recently replaced water pump w/stock unit with no changes.

 

I did not see what year vette you had or if you have done any modifications. I can tell you that my 78 L-82 4 Speed (pretty much stock except shorty headers and true duals) with 3.70 gears which I have owned since 1983 always had a problem getting hot on the highway (3,500 RPM @70 MPH) until recently. Before I tell you how I solved the problem, I would like to run through a littany of things changed that DID NOT solve the problem until recently:

1. Replaced OEM radiator with another copper/brass one (no change)
2. Replaced water pump with OEM type water pump (no change)
3. Replaced fan clutch (no change)
4. Robertshaw thermostats, 160 and 180 (no change).
5. Verified timing static, mechanical, vacuum and total advance (no change)
6. Water wetter (no change)
7. Front spoiler extension from 79 corvette (no change)
8. Correct lower hose (no change).
9. Checked and reinforced all radiator airflow seals (no change).

At 70-80 MPH on a 90 degree day the temp would creep to about 225 degrees on the highway only, not driving around town, which indicates to me a radiator capacity issue, airflow issue, or both. Incidentally, GM changed the 12 O'Clock reading on the temp gauge in 1979 from 200 (1978) to 225, I believe, since the L-82's were running so hot and they were probably getting questions and complaints from customers when the cars were new!

This year I replaced the OEM type radiator with a Dewitts Aluminum replacement, a stewart stage 2 water pump, and a Robertshaw high performance 180 thermostat (holes drilled in the thermostat for flow when closed). Car now runs in the same conditions about 185-190 on the highway and 175-180 around town.

I think that the mid 70's to 80 vettes have three things going against them, especially vettes that rev high on the highway with high numerical gears:

1. Smog heads do not flow water or cool efficiently! GM wanted the temp high to burn emissions!
2. Radiator capacity is inadequate for the revs on the highway combined with the poor air intake of the sharks (starting in the early 80's, the C3 got aluminum radiators (I think) and revved much lower on the highway thus less air requirements needed.

3. As stated above, too many revs for the radiator capacity. Base cars with economy gears generally do not have a high temp issue, in my experience, if everything is functioning well.

I would definitely start with an aluminum radiator and NOT run the auto transmission lines into the radiator (automatic transmission fluid gets VERY hot on the highway) and would try to mount the biggest double stack (not tube and finn) cooler you can get into the grille area, to cool the tranny fluid (24,000- 28,000 GVW cooler, Long for example). I have a 1994 Mustang GT Auto that I disconneted the cooler lines from the radiator and run a Long double stack 28,000 GVW cooler only for the trans and was shocked at how much the engine temperature dropped while moving, changing nothing else.

Hope that this helps!

 

Well then, why would you look anywhere else but here?

 

I missed that point! Sounds like a definite radiator issue if nothing else changed although totally perplexed why going from a 3 to 4 row would make it run hot! I agree!

 

Don't know much about 4-row style radiators, but is the core thicker than 3-row style ones ?
If it is, this could be some kind of air flow restriction ???

 

Running warm on the highway has nothing to do with the clutch fan and everything to do with the radiator. I would be looking at a Dewitt's radiator.

 

When you replaced the radiator, did you leave off the gaskets around it?

 

This spring I had to to replace my stock L-48 engine (2 colapsed lifters/wiped lobes) in my '80. Installed a GMPP 350/330HO engine. Had stock 3 row radiator re-cored to a 4 row. With 180 degree thermostat at idle with 70 degree air temp. I have 50 degrees of cooling from top radiator hose to bottom radiator hose. Automatic transmission cooling lines go to radiator. Temp. stays between 180-190 @ 70mph/2800rpm.

Whats the temperture drop across your radiator?
All 4 row radiators are not created equal, ie, tube diameter, # of fins, fin spacing. Hope this helps.

 

Like Bashcraft pointed out, I definately figured it was the radiator. Unfortunately, a friend was in need of a radiator for his '76 and I had given the original radiator to him to use. Looks like I am stuck with trying to make this one work or upgrade to aluminum (kid in college makes it hard to do).

The four row is physically wider in the core area, but the tanks are about the same size so it fits the radiator support. I dont think it will restict flow, but the extra back tubes may not transfer heat as well.

71270HP has it right about not being created the same. Mine, I found out later has about a 10 fin/inch count where better radiators have a higher (14 + fin/inch) count.

I installed seals when I installed the new radiator and have the factory spoiler in place.

Thanks for all the input. At least I am not crazy in trying to solve this issue.

 

Sorry, reading through some posts and didn't answer some questions.

the car is a '77 L-48, 4-speed car. It has A/C (condensor hindering air flow) and is stock.

It's been awhile since the IR, but I think drop was about 30 F across radiator.

 

That's true, but a good clutch fan will stop in less that 1 revolution after a 15 minute drive.

The thermostat only controls the minimum operating temperature but I would still start with a new Mr Gasket 180* fail safe.

You say the problems started only after going from a 3 row to a 4 row radiator, is it possible that the 4 row holds less coolant than the 3 row? PG.

 

One last thought, you said all the seals are in place, are you sure that the one on the top of the radiator seals tight when the hood is closed? PG.

 

Air cleaner has an intake scoop that sits on top of the radiator support and is roughly a foot wide. I have the seals starting on either side of the air intake and running to the channel at the edge of the hood. These "filler" pieces have been compressed to the shape of the underside of the hood, so I would say my upper seal is a good one.