Overheating issue - I am stumped!

[Mattchu60]

I will try to get a picture, but I didnt change anything over the stock setup for the heater hose - disconnected the one from the intake when I removed the engine, hooked it back up with I re-installed. The radiator has a connection point for the coolant to flow into the radiator after it passes through the heater core.

Its like this on mine - leaves the intake near the thermostat, routed into the heater core, leaves heater core and travels to the radiator, leaves radiator and travels to the water pump. This is the stock setup from what I see.

[Custom.Chevy]

i really wish the heater hoses on the c10 were the same size. im also running a serpentine belt system on a newer block. my heater core is way bad and leaking on my floor. thank god i rhino lined my cab floor! I"m currently in escrow from selling my home and buying another so i have no access to tools or a garage, does anyone know any good tricks to bypass the heater core so i can still drive my truck. its summer anyhow no need for it.

[ironroad9c1]

OK first off factory gauges are there for Amusement only , get a real temp gage for that spot in the head, you can even just get a cheap mechanical one and hook it up temporarily and take a drive, , the fan clutch , usually only causes overheating at slow times like in stop and go traffic, the fan clutch is only slightly engaged when the engine is at speed moving down the road, you can check it by revving it up from under the hood watching the fan, you should be able to tell its disengageing at higher rpms and reengaging when you bring it back down to idle, also its hard to get a good quality tstat nowadays being as everything has moved offshore, and last if the intake manifold is showing the correct temp the rest of the engine will be pretty close to that temp. once everything is warmed up. also new engines tend to run a tad warm until everything breaks in.

[rich weyand]

This plus a foot of both hose sizes (3/4 and 5/8) and a couple clamps gives you your bypass.
http://www.autozone.com/fittings-and...or/102831_0_0/

[Katrina/10]

I find this interesting because I put a complete 87 engine with TBI into my 71, and the temp gauge does exactly the same thing as yours! I have had many carbureted V8s over the years, but none of them ever did this. Aftermarket mechanical gauge in the dash reads 230 degrees before the thermostat opens, then goes to 200. I have a 195 thermostat installed, which I did switch out for a new one, with no change. I was considering drilling a hole in it until I read it had no effect on Matt's truck.

I don't like seeing the gauge go up so high either, but I could not think of anything else to do with it. So, I have been driving the truck for two years, and it has not caused any problems. It just puzzles me why this would happen.

[Mattchu60]

I am going to try a 180 Stat over the weekend. I dont know if it will help or not. One of our theories is that the since the heads are iron and the intake is aluminum the intake is cooling a little more than the heads which is causing the stat to open slower.

Doesn't really seem like coolant would drop 20-30 degrees within a few seconds though as it travels from the head to the intake. Starting to think more and more that its just faulty gauge readings. I have another temp sender coming to try as well. Thought about putting a mechanical gauge in the head to see what it reads in the future.

[cadillac_al]

The coolant isn't moving when the the thermostat closed. The coolant in the head is cooking while the intake warms up. It seems perfectly normal to me. My truck gauge doesn't do it because it is the stock gauge for amusement but does settle on a normal range every day like clockwork.. Rich Weyand has be intrigued once again with his theory of "improved routing" of the heater hose. It makes perfect sense but I probable won't change mine either since my trucks and cars seem to warm up within 2 miles anyway. In my experience the heater hose was routed to the radiator in heavy duty applications and big luxury car applications. It may even have better flow through the heater core but never spent much time thinking about it.

[Dead Parrot]

There is some flow through the heater core even if the t-stat is closed. Given where the output to the heater is, it might favor the passenger side head and account for the driver's side head spiking a bit before the t-stat opens.

My truck has an aluminum performer intake and I haven't noticed any temp spiking. Standard sample size of 1 disclaimer.

[Gotenntitans]

Hope it's not a head gasket. That happened to my 97. GTT

[nonstop]

My big block runs hot with a 195 thermostat, but just about right with the 180. With that said, I am still leaning toward a thermostat issue since there is a spike, then it drops and settles.

[Dc42d76]

Have incorrect intake gaskets been ruled out ? 88 and up engines use a reverse rotation water pump driven by the smooth side of the serpentine belt. This set up requires the rear cooling ports in the cylinder heads to be blocked,the 88 and up gasket will come with the block off built in and will be marked rear on the gasket. Looks like your 87 water pump is driven by the ribbed side of the belt so this would be a standard rotation pump, so all 4 cooling ports need to be open for this setup. I have also seen these gaskets installed incorrectly with the rear section of the gasket facing forward blocking off the front cooling ports. Kinda think something like this is going on.

[Mattchu60]

180 stat didn't change anything, just runs cooler after my temp spikes.

I am going to try Rich's idea of an external bypass. Trying to determine how to best rig one up. I'd like to leave the heater core bypass in place and use the hole on the driver side of the intake and run it to the water pump, this way I'd have coolant bypassing on both sides of the motor.

[78trk]

I had a 350 that did the same thing one day going to work. I did everything you did including taking thermostat out. The key was it only happened on start up. Then temp dropped to normal. It was a cracked head. Found it when I took the heads to head shop. I think crack was open and then closed when temp came up.

[rich weyand]

Originally Posted by Mattchu60

180 stat didn't change anything, just runs cooler after my temp spikes.

I am going to try Rich's idea of an external bypass. Trying to determine how to best rig one up. I'd like to leave the heater core bypass in place and use the hole on the driver side of the intake and run it to the water pump, this way I'd have coolant bypassing on both sides of the motor.

That, or try routing the heater hose return to the water pump and get the radiator reservoir out of circuit. The water jacket should heat up faster, before hot spots develop, and open the thermostat.

Both are worth trying. Take the one with the best results. There must be a reason the General changed the heater hose routing.

I'm thinking those heads have no internal bypass, or the gaskets don't accommodate it. Something is going on, because I have none of these issues. The differences in my setup: heater hose routing, and stock heads.

[Desert1957]

I would like to mention something I noticed on the pics just posted.
My 87 has that steel line shown at the rear of the intake manifold / passengers side, Coolant comes out of the intake at the rear port, through the heater core,returns to the water-pump.

maybe should be hooked up like pic below.



Desert

[wilkin250r]

I highly doubt the heater hose routing is causing an overheating problem. Yes, the heater core will dissipate heat, and it will technically help cool the engine, but not a significant amount. IF the temp gauge is accurate and it's climbing to 250 degrees, the best heater core performance wouldn't bring that below 240.

By all means, fix the heater hose routing, but I wouldn't expect it to cure your problem. There's still something going on, whether it's a faulty temp gauge, or bad thermostat, or water flow problem. I doubt the heater core flow and routing will affect anything more than a few degrees.

[Mattchu60]

Been on vacation for a week, got back home yesterday and had a few packages in the mail with my brass fittings. I installed them today and made a bypass from the intake manifold to the water pump, I also put a proper heater hose connector in and ran new hoses for the heater core.

After 2 drives I believe the problem is solved, the temp does not get over 210 on the gauge now (running 195 stat). It was obviously not circulating coolant evenly around the heads in the old setup before the T-stat opened which was creating a hot spot.

Thanks for all your help, I am glad this is solved because it made me very nervous to see that gauge climbing all the time on startup!

I'll try to get a picture up of the engine bay now, looks a little cleaner.

[rich weyand]

It's not the heater core dissipating heat. The issue is that there needs to be circulation within the engine before the thermostat opens, to eliminate hot spots and to ensure the thermostat sees the heat it needs to open. So there has to be circulation. To that end, the stock heads have a bypass, that routes water around in the engine when the thermostat is closed. The heater core can also serve as such a bypass. The issue here is the the OP does not have correct coolant circulation within the engine.

[WyattTX]

This may sound ridiculous, but do you have a fan shroud? If not, put one on, that would make things a little cooler.

[Katrina/10]

I don't think it makes any difference if the heater core is connected to the front, back, or not at all, as I have run many engines with no heater connection and never had this issue. It has to be something in the engine itself.

[rich weyand]

Summit confirms that those heads have the internal bypass. I have not been able to confirm whether the Fel-Pro 501SD gaskets have the bypass holes, but I would be surprised if they didn't.

Another thought occurs. Is your radiator stock cross-flow, or is it a serpentine radiator (rare, but thought I would ask)?

[Mattchu60]

Thanks for checking that for me Rich. I was hoping to have a bypass to the water pump put together by now but I have had no luck getting fittings for the hoses, all the parts stores have are steel fittings and I would like to have brass, the local Menards plumbing section didn't have anything either. Going to have to go online to get what I need, so it'll be a week or so before I can report back again.

The 180 stat is helping some, gets the T-stat open faster so I am not getting to 250ish degrees now, saw 230 today then it dropped.

[Dead Parrot]

For testing, steel should be fine. If it fixes the problem, then order the parts you want long term. Be sure you leave a bit extra on the hoses if you go this route.

It will suck if you wait and worry a couple of weeks while the brass parts show up only to find out they didn't solve the problem. And you will know exactly what parts to order.

[Katrina/10]

Originally Posted by rich weyand

Summit confirms that those heads have the internal bypass. I have not been able to confirm whether the Fel-Pro 501SD gaskets have the bypass holes, but I would be surprised if they didn't.

Another thought occurs. Is your radiator stock cross-flow, or is it a serpentine radiator (rare, but thought I would ask)?

Can you describe any more about these bypasses? Where are they, how do they work?

[rich weyand]

There ya go! Congrats.