Over heating in high RPM

[Datsundude]

Hi all,

I have over heating issue with my 69 SPL roadster (R16 motor), can anyone please help?
Here are the symptoms…. when I cruise on the freeway going about 60 to 75 miles per hour I can see the temperature meter rising rapidly to almost to the max (over heating) it will over heat if I continue driving it.
I get slightly over heat when I’m going in low speed like cruising around the neighborhood for hour in normal driving not pushing the car in high RPM.
it seem to be normal when the car is in park and idling at 900 to 1000rpm (25 minutes)



Recently head swap (not a rebuilt head) with new head gasket and adjusted the valve a month ago
Drained and put in new coolant (50/50 mixed)
Timing is set at between 15 and 16 degree on the very last mark on the pulley.
I have rich the fuel mixture and that didn’t change anything.

Any suggestion will be appreciated.

Thanks
Vinh

[SLOroadster]

Did you burp the cooling system? If not, you had a big air bubble and now you need some more coolent. Another thing to check is your thermostat. Finially what shape is your water pump and radiator in? Beyond that it looks like you are in the right ball park.

Will

[Datsundude]

Hi Will,

Thanks for responding to my questions…
Thermostat- I’ve been trying to replace it but couldn’t figure out how to remove the thermostat housing yet… it is not over heating when the motor is at idling, I figure is not the thermostat, Right?

Water Pump- look like it had been replace time ago, cause I do see new seal on it.

Radiator- had been gone through by radiator shop.

Burp the cooling system- This might be a possibility here, how do you burp the cooling system?

Any more suggestions?

Thanks
Vinh

[keith0alan]

Mine would do that. When I had the radiator redone I had a high density core put into it. Problem solved. The stock 1600 radiator doesn't have a lot of surface area. The high density one has about twice as many squiggles between the tubes. Also as radiators age the fins come loose from the tubes. This reduces heat transfer. It might flow fine but the heat just doesn't get out.

keith

[bmccarthy67]

Will's "burping" suggestion is the quickest check...take off the filler cap and use a long screwdriver to push the thermostat open..this will allow air to vent out, then fill the void with more coolant and repeat...I also used some water wetter (I think it's made by red line)...it helped lower the temp a few degrees. I drive in Savannah, GA and it gets pretty darn hot here, but this seems to be working...good luck.

Buddy

[itsa68]

Is the air scoop still attached to the bottom of the rad?
Sometimes they are removed and not replaced, so not as much air is directed into the rad.

Ray B.

[Datrock]

These ideas may affect the cars temperature..

First the obvious, is your fan belt tight.

Do you have a recurved distributor to a 7.5 degree cam. The car will run hotter if you dont recurve the dist after removing the pollution stuff.

What kind of fan setup are you running? If it's the original setup the clutch in it could be failing.

Do you have the head to radiator crossover tube, which I believe is needed, unless you are using a 2L radiator.

As already mentioned, it does seem to take quite awhile to fill the coolantsystem on these cars.

Hopefully these ideas may helped...Bill

[eastmedia]

Hi vinh,

First off check the temp guage and see if it's really overheating. Get yourself a meat thermometer and when it gets hot pull the radiator cap off and stick the end of the termometer in there and check the actual temp. My guage reads about 210 but the actual water temp is 170. Go figure.

If it is high (above 190) it could be your thermostat is not opening. It should only take about 15 minutes to change it. Good luck.

I'm in whittier so if you need help PM me and we'll get together.

Ron

[Datsundude]

Hi guys,

Thank you all for the suggestions I appreciated.

Air scoop is still attached to radiator.
Fan belt is tight, I just check the other day…
I am running the original stock fan with four blades

Last night I removed the thermostat housing to inspect the thermostat and guess what? The thermostat was rusted up and a lots of debris
covered the outlet and that probably slow the water flow.
I’ll put it back together tonight and see if it still over heating, I might go without thermostat…. I’ll let you guy know the result on this.

By the way I broke one of the stud when I remove the thermostat housing, good thing I have extra parts in the garage.


Thanks
Vinh

[keith0alan]

That's another place I like to put stainless steel studs. You just can't keep water from getting around the stud. Rust fills up the space welding the whole mess together.

[Datsundude]

Dude,
Tell me about it… doubling the nut together wont loosing up this stubborn stud (lucky its only one)…at the end I have to used vise-grip and the stud broke where just it coming out from thermostat housing. I had to twist and pull, take about ½ hour to remove the housing out.


Vinh

[keith0alan]

Yep, been there done that. One thing I've done is take a 1/16" drill and drill down between the stud and the housing. That way you remove the rust packed between the two. That also gives the penetrating oil someplace to go. If you don't go with stainless you can clean the studs, paint them and pack grease around them as you put it together. With grease between the stud and housing the rust will be kept at bay for a little while anyway.

[spl310]

If you found rust gumming up the works, you have another issue to contend with. Using a LARGE long screwdriver, open the valve on the intake side of the block - it is below the manifolds between the number 3 and 4 cylinders. More water should flow out. If it does, then use clear tap water to flush the block. One of the Prestone flush kits is a good thing for that as it flushes the entire system.

If water doesn't flow out, then you will have some fun. You need to get some engine cleaning brushes. They are an assortment of different size long bottle brushes. Pull the head and stuff rags down into the pushrod ports to keep water out. Put water or coolant into the water passages and scrub them out. It will be a nasty brown mess, but you need to get the rust buildup out of the block - particularly by the rear cylinders. They are likely getting much hotter as the water flows more poorly back there. Once all is cleaned out, back flush the radiator and heater core (reverse flow - easier on the rad if it is out and upside down...) and then put it all back together using the proper thermostat and coolant mix.

[MccStyle]

In my race car i found that my lower hose was colapsing. Not good for high speeds. After chaseing my tail around and spending lots of money all I had to do was put a wire in the lower hose and presto. 130 mpr at 190 deg.

Todd

[Datsundude]

Hey guys,

No luck on resolving the over heating issue… I changed the thermostat (spring down) didn’t make any difference… used premium gas (91 octane)
No difference. Adjusted timing to 8 degree (was at 16) no change on over heating however I do feel the car is pulling harder then before in terms of power.
Retorque the head after test run to 45-50 pound no differnce.


Well perhaps I can give a little more detail if that would help.
Like I was saying, it get over heating or perhaps I should describe as running too hot… cruising down on the highway starting at 3k rpm and higher.
I’m guessing the temperature would be somewhere at 220 degree and will probably get to 250 if I continue cruising on the highway, it will continue running hot at 220 degree even though I exited the highway driving in low speed, so in other word it continuing running at 220 degree until motor is shut off.
The temperature meter would be on very close to 250 degree ,I have not seen it gone up to 250 yet but I assume it would if I continue cruising on the highway.
When the car is warming up from sitting over night, it would take some time (15-20 minute) to get warm up.


I have not tried using meat thermometer yet but that will be my next thing on my to do list.
Replace temperature sending unit see if that change anything.
Test out the temperature meter on my car.

Anyone have any more suggestion?

Thanks
Vinh