[bobbycjr]

I know it will be hard to diagnose without seeing the vehicle, but I tried to take my Can Am to a cruise-in about an hour away, and after about 15 to 20 minutes at 60 MPH, the temp. gauge kept creeping up beyond the 220 mark. I stopped and looked under the hood, and the radiator cap had a quiet hiss and the overflow bottle filled up half way. There was no violent boiling over or anything. When I tried to crank the car, it strained to turn over (it wouldn't turn over actually), so I went inside and ate. When I came back out, roughly an hour later, the overflow bottle was empty, the radiator was full, so I cranked the car and drove home at 50 MPH. The temp. seemed more stable at less than 220. Not until I got almost home did it get even close to being straight up 220. I pulled the car in the shop, shut it off and cranked it a couple of times, and everything seemed to be ok. The overflow bottle stayed almost empty. The engine is supposedly rebuilt, the radiator is new. I don't know about the thermostat and water pump. That's where I figured I would start my investigation. Any guidance would be appreciated.

[77 Canamman]

I would check the timing. From there I would replace the T-Stat, pull the water pump, and make sure you have a pump with a cast iron impeller. Check the o-rings in the front cover. They are usually hard and cracked. Make sure that the water pump spacer isn't rotted. Check the fan clutch to make sure that it is tight. Make sure the air dam is present on the bottom of the radiator support. Flush the system, as there may be buildup in the system.

[bobbycjr]

Originally Posted by 77 Canamman

I would check the timing. From there I would replace the T-Stat, pull the water pump, and make sure you have a pump with a cast iron impeller. Check the o-rings in the front cover. They are usually hard and cracked. Make sure that the water pump spacer isn't rotted. Check the fan clutch to make sure that it is tight. Make sure the air dam is present on the bottom of the radiator support. Flush the system, as there may be buildup in the system.

Thanks for pointing me in the right direction.

[77 Canamman]

Also, I forgot to mention to pressure test the cap, and or replace it, and make sure that you are using a 50/50 mix of coolant.

Another thing, I would make sure that it is really overheating, The stock gauges were never noted for their accuracy. If you have to replace the sending unit, use only a high quality replacement from Lectric Limited or NOS GM.


TEMPERATURE SENDING UNITS

A New Solution To An Old Problem!
Is your car running too hot?
Maybe your temperature gauge is not telling you the truth.
Most cars have had their temperature sending unit replaced with a GM/Delco or an
auto part's store replacement temperature sending unit. This may be your problem!





Lectric Limited now offers accurate temperature sending units for many Chevrolet, Buick, Oldsmobile, Pontiac & Cadillac vehicles. Months of research were devoted to this project in order to provide our customers with sending units that have the original-type terminal connection, housing and resistance (thermistor); resulting in an accurate gauge reading. They screw right into the 1/2" (not 3/8") pipe thread hole (as original).

Both auto part's stores and GM/Delco do sell replacement temperature sending unit, but they do not produce an accurate gauge reading in vintage cars. This is because sending units from an auto part's store and even GM, are only a generic replacement; often requiring a new, matching gauge or re-calibration of your original gauge.

Please Note: The terminal connections on all our sending units are exactly as-original.
Through the years, the mating terminal & connector on your harness may have been
changed by you or a previous owner. This change was most likely made in order to try
different sending units when the "exact replacement" unit didn't work or was not available.
If your harness had been modified from original, we do offer replacement
Temperature Sending Unit Lead Repair Kits. (See our “Repair Components” section.)

Consult our on-line catalog & order form for your application & price.

Made in U.S.A.

[bobbycjr]

[QUOTE=77 Canamman;3560497]Also, I forgot to mention to pressure test the cap, and or replace it, and make sure that you are using a 50/50 mix of coolant.

Another thing, I would make sure that it is really overheating, The stock gauges were never noted for their accuracy. If you have to replace the sending unit, use only a high quality replacement from Lectric Limited or NOS GM.


You're right. I've thought there was some inaccuracy in the gauge, and also due to the fact that the most noticeable result was the filling of the overflow bottle, and no other violent effects, that it might not be actually running hot, but showing some signs of running hot. I appreciate the info on the sending units.

[bobbycjr]

Originally Posted by 77 Canamman

I would check the timing. From there I would replace the T-Stat, pull the water pump, and make sure you have a pump with a cast iron impeller. Check the o-rings in the front cover. They are usually hard and cracked. Make sure that the water pump spacer isn't rotted. Check the fan clutch to make sure that it is tight. Make sure the air dam is present on the bottom of the radiator support. Flush the system, as there may be buildup in the system.

One thing I forgot to mention in my original post is that the radiator is filled right up to the inlet opening. It is a reproduction radiator, so it doesn't have "Full Cold" and "Full Hot" indicators on the side like a Harrison radiator would. I know that in my experience with Chevelles, if you fill them up to the top, they will "puke" a little coolant when you park them after driving a while. I just wondered if I needed to syphon a little coolant out, because maybe there's too much in the radiator. Also I checked the fan clutch by trying to spin the fan, and it has a lot of damping to it, and no looseness, so I guess it's ok.

[77 Canamman]

On a vehicle with the closed coolant system with an overflow tank, like your Can Am, the radiator must be full, so there would not be a full cold mark on the radiator. Look at your tank. When the car is cold, make sure that the tank has coolant up to the full cold mark. Make sure you have the correct 15 lb radiator cap. If the radiator/coolant tank is not full, air will get into the system.

[bobbycjr]

Originally Posted by 77 Canamman

On a vehicle with the closed coolant system with an overflow tank, like your Can Am, the radiator must be full, so there would not be a full cold mark on the radiator. Look at your tank. When the car is cold, make sure that the tank has coolant up to the full cold mark. Make sure you have the correct 15 lb radiator cap. If the radiator/coolant tank is not full, air will get into the system.

Thanks. A 16lb vented cap is on the car now.

[camerjeff]

The only thing I can add to what has already been said, is when you have you water pump out, and are checking the spacer & transfer tubes, even if you have a cast impeller on the pump, and no holes ect in the spacer, check that the clearence on the spacer to the impeller is not to large. It only needs to be a couple .002 thousands of an inch. If it is to large it affects the pump.
Also I usually run a Robert Shaw High flow thermostat. those 2 things have solved several Pontiac overheating issues for me.

[bobbycjr]

Originally Posted by camerjeff

The only thing I can add to what has already been said, is when you have you water pump out, and are checking the spacer & transfer tubes, even if you have a cast impeller on the pump, and no holes ect in the spacer, check that the clearence on the spacer to the impeller is not to large. It only needs to be a couple .002 thousands of an inch. If it is to large it affects the pump.
Also I usually run a Robert Shaw High flow thermostat. those 2 things have solved several Pontiac overheating issues for me.

Thanks for the additional info. All of this has been a gret help.

[cdrookie]

there's a thread on this site that says to make sure your upper rad hose isn't above the rad cap. a few guys had their hoses hump up about 4" above the cap and were overheating, they changed the hose and were fine.

[bobbycjr]

Originally Posted by cdrookie

there's a thread on this site that says to make sure your upper rad hose isn't above the rad cap. a few guys had their hoses hump up about 4" above the cap and were overheating, they changed the hose and were fine.

I'm posting a picture of my upper hose. It looks ok to me. Let me know if I need to make some changes.

[77 Canamman]

The hose looks fine to me. The original GM hoses were bent differently, but that is the only hose that has been available for many years, unless you can locate a NOS part.

I do see one detail that is off. The hood release cable should be routed through the radiator support behind the battery, not on top as it is now.

[bobbycjr]

Originally Posted by 77 Canamman

The hose looks fine to me. The original GM hoses were bent differently, but that is the only hose that has been available for many years, unless you can locate a NOS part.

I do see one detail that is off. The hood release cable should be routed through the radiator support behind the battery, not on top as it is now.

Thanks on the hood release cable correction. I'm without an assembly manual on this car. I've tried to locate a new release cable, because this one's taped up, as you should be able to see in the photo.

[bobbycjr]

Originally Posted by 77 Canamman

On a vehicle with the closed coolant system with an overflow tank, like your Can Am, the radiator must be full, so there would not be a full cold mark on the radiator. Look at your tank. When the car is cold, make sure that the tank has coolant up to the full cold mark. Make sure you have the correct 15 lb radiator cap. If the radiator/coolant tank is not full, air will get into the system.

Just want to update you guys on the status of my car. Thanks to everyone for the help and suggestions. Everything has been very helpful.

Installed a Lectric Limited sending unit, Mr. Gasket high flow thermostat, and new radiator cap (16 lb., recommended by my mechanic). I drove the car 1 1/2 to 2 hours today, driving, coming back to the house, checking, idling, starting, etc. It seems that the gauge is at home at straight up 220 or maybe a needles width less at speed (60 to 65 MPH, with short bursts to 70 MPH). I would like to see it at less than that, but with all my driving this morning, the needle never went above that (until I shut it off, but it recovered quickly when cranked). The needle would come on down to the left of 220 when going through the neighborhood, and slower speeds. The radiator never overflowed, and I could not hear any hiss from the cap. It was relatively cool here today, never getting much above 50 to 55 deg., so it may behave differently on a warmer day. I did notice a red film on the old thermostat and sending unit, so a flushing is probably in order. It seems to have made quite an improvement over my episode last weekend, however.

[77 Canamman]

If the engine is fresh, it may run a little warm until it is fully broken in. Is the radiator a three or four row? The temps should stay around 200 when driven normally.

[Brian Baker]

I don't think these gauges were ever really that accurate. Bill Boyle conducted a test one time on his W72 '79 T/A and when the factory gauge was reading 220, the mechanical Auto-Meter gauge he had wired with it for comparison was reading between 200-205 if memory serves correctly. I have a 160 thermostat in my Can Am and the gauge always read well below 220.

[bobbycjr]

Originally Posted by 77 Canamman

If the engine is fresh, it may run a little warm until it is fully broken in. Is the radiator a three or four row? The temps should stay around 200 when driven normally.

My radiator is a four row, and is new. I'm probably going to flush the system next, then probably double check the timing. I saw on a forum on another site that some people are having good luck with a product called Water Wetter, that supposedly has better cooling characteristics than anti-freeze. I may try that as a last resort, if my first road trip, coming up soon, doesn't work out.

[bobbycjr]

I am still having trouble with this car of mine. I tried to drive it to a cruise-in about an hour from here on March 7th, and got about half way, and the car quit on me. We had just set the timing at 8 deg. BTDC. The temp. gauge was still registering high. The car actually shut off, after starting to skip a little. I looked under the hood, didn't see any violent behavior of any kind, and actually hit the starter, and the car turned over, fired a little, but I didn't start it immediately. I let it sit for about 45 min., then tried to drive it back home, but it was still skipping and acting weak. A friend of mine came to pick me and the car up, and he said by listening to the engine that I might have some sort of ignition or carburetor problem, but it didn't sound like the engine was messed up. Just for information purposes, the car has a DUI distributor on it, so I don't know if this is contributing to my problem or not. There are also a few ports plugged on the intake and carb., and I don't know what the effect of these might be. My next move will probably be to take the water pump off to check the rubber seal, maybe put the stock distributor back on, then if that doesn't work, I guess I'll take it to Classic Pontiac Rescue on Donalds, S.C. Maybe they are more familiar with these engines, and can help me out, I don't know. I am getting quite frustrated, as you folks might guess, because I have in my shop what is fast approaching a 20k boat anchor, that I can not drive. I am backing off the car for a while, to try to re-group.

[sport coupe]

The tree valve that is disconnected is listed as it controls the EGR and EFE thermal vacuum. Is the EGR disconnected? It would help if someone posted the emission control system vacuum diagram for the 77 400 to see how it should be connected.
Also you should get a bottom battery spacer and the battery hold down parts that are still available.