tbiga

I have a 65 convertible. The 327 had some issues so it came out. The current engine is a completely rebuilt 350, built to 1969/70 LT1 specs. Nothing to radical but some minor changes, overall its a pretty mild build. The temperature sending unit is not located in the intake or head but in the right side of the block just below the #6 spark plug. Its new, as is the 160 degree thermostat, waterpump is new and I'm running a 7 blade fan from a later model car.

I now have about 300 miles on the engine but it still seems that it wants to run hot. In town in traffic it starts to creep up and on the freeway running at 65-75 mph the temp will slowly climb to 240 maybe higher (the temp gauge is from a 66/67 that goes to 250). Today on the freeway everything came to a stop and it started to climb over 240 so I pulled off and let it cool. It takes several miles 20 or so before it starts to get really hot but steadily climbs to where I'm not comfortable. If i can get a chance I can push in the clutch and coast downhill the temp will drop but thats not always doable.

The only thing I don't have in place is the the fan shroud. Would that be something I need to direct the air for better cooling?

I'm no mechanic but I've done all the work to this on my own (its been a lot of fun so far). Not being an expert I'd like to know what else I can do to try and get it to run cooler.

midyearvette

the shroud is an important part of the cooling system, as is the proper clutch fan for the air flow the system was engineered to use....

65 vette dude

If you haven't done so, you really need to check the exact temperature on the top rad hose, just in front of the thermostat housing with a IR gun, and compare that reading with your temp gauge. You might find out your gauge is 20-40 degrees off. Then you'll get to do the "sending unit shuffle", like the rest of us.

narlee

Agree with the other posts. Get the shroud on, double check the actual temperature, and check your timing.

Frankie the Fink

Absolutely correct on the shroud. My C1 would run 'warm' until I packed the ill fitting, original shroud all around with foam pipe insulation (and eliminated the pesky fan clutch).

Kensmith

It should not climb on the freeway regardless of shroud. Yes, you need a shroud but I don't think that will fix the issue. Post all the information on the motor, radiator, water pump, timing, etc. But first, buy a IR gun and check the upper and lower radiator hoses, intake at the thermostat housing. Also water pump temps. Not sure why the sender is in the block? IMO it should be in the intake manifold or head.

JohnZ

The sender is in the cylinder head, not the block; that's where they were in 350's.

The shroud is important for idle and low-speed traffic cooling, but not for highway cooling; ram air over 30-35 mph provides all the airflow you need, and the fan is ineffective at that speed.

What kind of radiator do you have, and how old is it? A photo or two of the radiator and fan arrangement would be helpful.

1snake

You said you have a new sending unit. That's most likely the problem. Comfirm this with an IR gun.

Jim

tbiga

The engine is now kind of a mish-mash of parts. Head and intake are from an actual 70 Corvette LT1. When I started I also had the original block but it turned out to be to bad to salvage. Brand new pistons (.040 over) and rings reconditioned rods and crank.

The sending unit is in the side of the block because I didn't know better when assembling and the block i'm using is an early 80's 350 and that where I took its sending unit out of. If the location is causing issues I can move it but a couple others have told me the location shouldn't matter. But maybe the location is more of an issue since it would be reading a water temp further from the thermostat than what it should be. (there is no location to install the sending unit in the intake)

the radiator is brass and looks as if its been re-cored at some point but exactly when i don't know. I had it checked at a radiator shop before I put it back in and they said it was okay. I don't know if okay meant it didn't leak or if it also had good flow. Since the car is also an AC car the radiator is sized for that also.

I so need to not trust people to do the right thing when I take them something. I expected them to test it for flow and leak but maybe they only tested it for leaks. So it also in question.


From the advice I've gotten so far I'll relocate the sending unit to the head, get the radiator flow tested, and get the shroud installed. More work than I wanted but it has to be done.

JohnZ

The only sending unit used in a 350 block was a knock sensor, not a temp sending unit; the temp sender needs to be either in the cylinder head or in the intake manifold. In any event, you MUST check the accuracy of the sender and gauge by comparing the reading against an I.R. gun shot of the upper radiator hose just above the thermostat housing, especially if the original sender has been replaced - most cause gauge readings from 20* to 40* higher than actual, and you need to know what the gauge is really telling you before you proceed.

Chances are excellent that the replacement copper/brass radiator is the root cause of the problem (if it is indeed overheating); they have about 35% less cooling capacity than the correct Harrison stacked-plate aluminum radiator that was in the car originally, and the additional cooling load of the A/C just makes the mismatch worse.

Don't bother with a flow test - it's meaningless - all it says is whether the radiator is blocked or not; what matters is its cooling capacity (heat rejection capability), and we already know it's inadequate for the application.

You might want to read this before you go any further:

http://www.lbfun.com/warehouse/tech_...em/cooling.pdf

4440stevesvette

The timing has to be spot on. Retarded timing will make it run WAY TOO HOT!!!

tbiga

Thanks for all the great advice, I'm sure with this help I'll get it figured out soon.